Greg Hammer,Steven Hall,
Peter J. Davis
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Video Endoscopy, 685 |
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General Abdominal Surgery, 686
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General Thoracic Surgery, 699
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Urologic Surgery, 710
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Bariatric Surgery, 714
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Summary, 716 |
In this chapter, the anesthetic considerations of the most common general abdominal, thoracic, urologic, and bariatric procedures are summarized. Common surgical problems with practical suggestions and discussions of anesthetic technique and anesthetic concerns are offered.
For the most part, anesthetic considerations for pediatric general surgery are similar to those for adults. Inhalation anesthesia supplemented with muscle relaxants can provide adequate operating conditions. Nitrous oxide should be avoided in the presence of a bowel obstruction and in situations where one-lung anesthesia may render the patient hypoxemic. For those in whom aspiration of gastric contents is a major concern, either rapid-sequence induction or awake intubation should be performed. Because children about to undergo urgent emergency surgery frequently have fluid and electrolyte imbalances as well as underlying hemodynamic instability, a thorough preoperative assessment of the patient is essential. In addition to the selection of anesthetic agents to render the patient unconscious, the role of regional anesthesia in providing the child with perioperative pain relief has assumed dramatic opportunity in children. The details of these regional techniques of caudal, lumbar epidural anesthesia, ilioinguinal/iliohypogastric nerve block, penile nerve block, and intercostal nerve block are discussed in Chapter 14 , Pediatric Regional Anesthesia. The last factor that influences anesthetic management is the planned operative approach. As the frontiers of minimally invasive surgery expand, these new techniques can markedly influence the patient's cardiorespiratory stability and consequently the choice of anesthetic agents.
▪ VIDEO ENDOSCOPY
With the development of smaller instruments, progress in video technology, and growing experience among pediatric surgeons, video endoscopic surgery is being performed for an increasing number of pediatric surgical indications. Benefits of video laparoscopy and thoracoscopy include small incisions and scars, reduced surgical intervention and postoperative pain, earlier return of bowel function, and more rapid recovery ( Box 19-1 ) ( Reddick and Olsen, 1989 ; Soper et al., 1992 ; Soper et al., 1994 ; Steiner et al., 1994 ; Sawyers, 1996 ; Hunter, 1997 ; Danelli et al., 2002 ). Fiberoptic endoscopes that can be passed through a needle are now manufactured, and digital video signals can be electronically modified to yield sharp, detailed, color images with a minimum light intensity. Digital cameras are designed to maintain an image in an upright orientation regardless of how the telescope is rotated. They are also equipped with an optical or a digital zoom to magnify the image or give the illusion of moving the telescope closer to the object of interest. The smallest of telescopes use fiberoptics and are less than 2 mm in diameter. Two-millimeter disposable ports, mounted on a Veress needle, are used for introduction of these small instruments. Larger instruments and ports are used in larger patients and for more complex cases.
BOX 19-1
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Advantages of Video Endoscopic Surgery in Infants and Children |
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Another major advance in video endoscopic surgery is the development of the endoscopic suite in which all necessary wiring is in equipment booms, ceilings, and walls. The manipulation of digital images is controlled by voice or touch-screen command either from the operative field or at a conveniently located station nearby. High-quality digital images are displayed on flat panel monitors that can be positioned within a comfortable viewing range. Remote-controlled cameras can direct any view in the room to any of the monitors or to a remote site. Digital radiographs can be routed from the radiology department to the operating room, and consultants in remote locations can be viewed on monitors in the operating room so that the surgeon can see to whom they are speaking.
An additional feature of newer endoscopy suites is voice-controlled bed positioning. Robotic tools can be vocally directed to position telescopes in the surgical field for optimal viewing; these surgical “telemanipulators” facilitate microsurgery in confined spaces even in small infants. Other endoscopic robots are being developed for a wide range of surgical applications.
Copyright © 2008 Elsevier Inc. All rights reserved. - www.mdconsult.com
Motoyama & Davis: Smith's Anesthesia for Infants and Children, 7th ed.
Copyright © 2005 Mosby, An Imprint of Elsevier
▪ GENERAL ABDOMINAL SURGERY
Abdominal and thoracic pathologic conditions requiring surgical intervention may be caused by metabolic or endocrine disturbances, tumors, inflammatory processes, or embryologic disorders. Box 19-2lists abdominal conditions commonly encountered in pediatric general surgery.
BOX 19-2
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Abdominal Surgical Conditions Commonly Encountered in Pediatric Patients |
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▪ LAPAROSCOPY
Laparoscopic surgery involves the intraperitoneal or extraperitoneal insufflation of carbon dioxide through a Veress needle. A variable-flow insufflator terminates flow at a preset intra-abdominal pressure of up to 15 mm Hg. Once the abdomen is filled with carbon dioxide, the Veress needle is replaced by a cannula through which a video laparoscope is inserted. Additional ports are placed according to the surgical procedure undertaken.
The laparoscopic procedures that can be performed in infants and children are virtually unlimited. A list of operations currently being performed is shown in Box 19-3 . As surgeons gain experience with laparoscopic surgery, the time required to complete these operations decreases ( Fig. 19-1 ). The safety and efficacy of commonly performed laparoscopic procedures compared with alternative approaches (e.g., endoscopic, open surgical techniques) have been compared.
BOX 19-3
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Laparoscopic Procedures in Infants and Children |
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FIGURE 19-1 The “learning curve” for laparoscopic fundoplication. (Adapted from Georgeson KE, Inge TH, Albanese CT: Laparoscopically assisted anorectal pull-through for high imperforate anus: A new technique. J Pediatr Surg 35:927, 2000.) |
Laparoscopic gastrostomy involves placement of an umbilical port and a left subcostal cannula (the future site of the gastrostomy). The stomach is pulled to the abdominal wall and the gastrostomy is performed using the Seldinger technique ( Fig. 19-2 ). Operative time is approximately 30 minutes ( Tomicic et al., 2002 ). The risks may be less than those for percutaneous endoscopic gastrostomy (PEG) in small children because the procedure is done under direct vision. There is less trauma than with open surgery, and feedings are initiated within 24 hours. Laparoscopic fundoplication for the treatment of gastroesophageal reflux disease (GERD) is associated with a complication and recurrence rate comparable to or less than that for open surgery ( Esposito et al., 2000 ).
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FIGURE 19-2 Laparoscopic gastrostomy. The stomach is entered and pulled up to the anterior abdominal wall (A) and is sutured in place (B). The gastrostomy tube is then placed (C). |
The laparoscopic treatment of appendicitis in children has been controversial, particularly in complicated cases (e.g., gangrene, perforation). Experience indicates, however, that laparoscopic appendectomyis not associated with an increased risk compared with open surgery, even in the presence of perforation ( Meguerditchian et al., 2002 ). The incidence of wound infections and intra-abdominal abscesses may be less in laparoscopic versus open appendectomy ( Paya et al., 2000 ). Surgical times are comparable and postoperative pain and length of hospital stay are diminished ( Canty et al., 2000 ; Lintula et al., 2001 ). Comparable results have been reported for laparoscopic cholecystectomy ( Esposito et al., 2001 ) and laparoscopic splenectomy in pediatric patients ( Danielson et al., 2000 ; Park et al., 2000 ). Diagnostic laparoscopy and laparoscope-guided cholangiography are being used in the evaluation of neonatal conjugated hyperbilirubinemia, avoiding the need for laparotomy and operative cholangiography ( Hay et al., 2000 ).
The role of laparoscopy in the treatment of solid neoplasms is evolving. Indications include biopsy of suspected malignancies, staging or determination of resectability, “second-look” procedures to help determine response to chemotherapy, and diagnosis of recurrent or metastatic disease ( Sailhamer et al., 2003 ). Laparoscopic tumor ablation or curative resection may have a role in selected cases. Open surgery may be required in cases wherein complete resection of the intact specimen with delineation of surgical margins is part of the protocol design in patients enrolled in multicenter studies. Although advocates of laparoscopic surgery maintain that laparoscopic surgery can reduce hospital costs, promote earlier patient discharge, produce less postoperative pain, improve cosmetic results, and allow patients a more rapid return to full activity, evidence for this is questionable so far ( Rangel et al., 2003 ).
▪ ANESTHETIC CONSIDERATIONS
Although regional anesthesia may be used alone in older children, general anesthesia is nearly always used for laparoscopic procedures. The use of the laryngeal mask airway (LMA) has been described in adults undergoing laparoscopy. The reliability of the standard LMA to provide adequate gas exchange during positive pressure ventilation is controversial ( Maltby et al., 2000 ; Lu et al., 2002 ). More favorable ventilation and a reduction in inadvertent gastric insufflation have been reported with the LMA-ProSeal (The Laryngeal Mask Company Limited, Henley on Thames, UK; Maltby et al., 2002 ). In infants and children, however, endotracheal tube (ETT) placement remains the standard.
Following tracheal intubation, the stomach is suctioned with an orogastric tube to decrease the risk of visceral injury during trocar insertion. The surgeon may prefer to place the patient near the foot of the table, especially for procedures in infants. The table position itself may need to be changed repeatedly during the operation, and both the Trendelenburg and the reverse Trendelenburg positions are often used. Accordingly, care must be taken to secure the patient to the table (e.g., using rolls of gauze and tape) while ensuring that the extremities are well padded and are not subject to inadvertent movement and untoward pressure during the operation. Inadvertent endobronchial intubation may occur due to cephalad displacement of the diaphragm associated with the Trendelenburg position and/or abdominal insufflation with gas. As a part of routine monitors, a precordial stethoscope should be placed over the left chest to readily detect this complication.
A variety of general anesthetic techniques have been used for laparoscopic surgery. Regional anesthesia is not commonly used as an adjunct to general anesthesia in pediatric patients unless the laparoscopy is converted to an open procedure. The use of nitrous oxide is controversial. Concerns have been raised that nitrous oxide may cause bowel distention, compromising visibility and exposure during surgery (Eger and Saidman, 1965 ; Cunningham and Brull, 1993 ). In addition, nitrous oxide may exacerbate the already increased incidence of nausea and vomiting following laparoscopy ( Divatia et al., 1996 ;Tramer et al., 1996 ), although the findings of several studies have failed to confirm these effects of nitrous oxide ( Taylor et al., 1992 ; Jensen et al., 1993 ). However, nitrous oxide can also support combustion. Because of its antiemetic effect, propofol has been recommended for maintenance of anesthesia during laparoscopy ( Song et al., 1998 ). The combination of propofol and remifentanil has been advocated due to rapid emergence without an increase in postoperative nausea and vomiting compared with the use of inhalation anesthesia ( Grundmann et al., 2001 ). Because of the increased incidence of postoperative nausea and vomiting associated with laparoscopy, prophylactic treatment with antiemetics and histamine blockers (droperidol, metoclopromide) have been commonly used. Orogastric suctioning at the end of the operation may also help reduce the risk of postoperative nausea and vomiting.
Because of the reduced postoperative pain associated with laparoscopy compared with open surgery, postoperative analgesia can usually be achieved with intravenous and oral agents. Although diminished compared with open surgery, pain following laparoscopic surgery is associated with incision, visceral manipulation, irritation and traction of nerves, vascular traction and injury, presence of residual gas in the abdomen, and inflammatory mediators ( Alexander, 1997 ). Pain is frequently localized to the back or shoulder.
A variety of approaches to prevent and treat pain after laparoscopy have been described. Bupivacaine infiltration at incision sites before skin incision has been shown to decrease postoperative pain ( Kato et al., 2000 ; Moiniche et al., 2000 ). Bupivacaine infiltration has been found to be superior to intravenous fentanyl or tenoxicam in reducing postoperative pain ( Salman et al., 2000 ). “Low-dose” intrathecal morphine and bupivacaine also decrease postoperative pain ( Motamed et al., 2000 ). Intraperitoneal local anesthetic instillation and mesosal- pinx block may diminish postoperative pain after laparoscopy and may be beneficial in reducing postoperative shoulder pain ( Kiliç et al., 1996 ). Intraperitoneal instillation of both bupivacaine and meperidine has been shown to be more efficacious than the combination of intraperitoneal bupivacaine and intramuscular meperidine ( Colbert et al., 2000 ).
Caution must be used to avoid toxic plasma concentrations of local anesthetics due to systemic absorption in infants and children, however. Perioperative acetaminophen, nonsteroidal anti-inflammatory agents, and other nonopioid analgesics should be used in combination with opioids as needed for postoperative analgesia. Clonidine has been shown to reduce the requirement for postoperative opioids and also has the advantage of decreasing the tachycardia associated with pneumoperitoneum ( Yu et al., 2003 ).
Physiologic changes during laparoscopic surgery are related to positioning (Trendelenburg, reverse Trendelenburg), increased abdominal pressure due to gas insufflation, and increased arterial carbon dioxide tension associated with insufflation. The magnitude of physiologic changes associated with laparoscopic surgery is influenced by the patient's age, underlying myocardial function, and anesthetic agents. The reverse Trendelenburg position may cause hypotension, especially in the anesthetized patient with intravascular hypovolemia. The Trendelenburg position causes cephalad displacement of the diaphragm, restricting lung excursion and posing the risk of endobronchial intubation. In addition, central venous pressure and heart rate increase, and systemic arterial pressures and cardiac output decrease ( Hirvonen et al., 1995 ). The pulmonary effects depend on the patient's age, weight, pulmonary function, degree of Trendelenburg position, anesthetic agents, and ventilation technique. Atelectasis and a decrease in functional residual capacity and pulmonary compliance may be observed. Ventilation/perfusion mismatch may result in decreased arterial oxygen tension. Neuromuscular blockade, endotracheal intubation, and positive pressure ventilation may help to reduce the pulmonary effects of Trendelenburg position. As long as intra-abdominal pressure is kept below 15 mm Hg, oxygen saturation can generally be maintained during position changes and pneumoperitoneum despite adverse changes in respiratory mechanics ( Sprung et al., 2003 ). Significant hypercarbia may occur despite adjustments in mechanical ventilation, especially in infants.
Both pneumoperitoneum and the Trendelenburg position reduce femoral venous flow, increasing the risk of thrombotic complications ( Rosen et al., 2000 ). Cardiovascular instability associated with laparoscopy has also been attributed to hypercarbia-induced arrhythmias, venous gas embolus, compression of the vena cava, pneumothorax, and pneumomediastinum. Insufflation to an intra-abdominal pressure of 12 mm Hg can cause septal hypokinesis, and left ventricular wall motion abnormalities ( Huettmann et al., 2003 ; Hoymork et al., 2003 ). The increase in intra-abdominal pressure associated with gas insufflation results in increased intrathoracic pressure and increased pulmonary and systemic vascular resistances, and decreased cardiac output ( Hirvonen et al., 1995 ; Hirvonen et al., 2000 ). Arterial blood pressure may be decreased, maintained, or even elevated by an increase in systemic vascular resistance. Reduction in splanchnic, hepatic, and renal blood flow and increases in the plasma concentrations of catecholamines, cortisol, prolactin, growth hormone, and glucose levels have been reported with carbon dioxide pneumoperitoneum ( Hashikura et al., 1994 ; Mikami et al., 1998 ; Ishizuka et al., 2000 ).
Hypothermia is avoided by warming the insufflating gas and/or maintaining insufflating flows of less than 2 L/min.
A new technique known as gasless laparoscopy eliminates the risks of pneumoperitoneum by using mechanical retraction ( Canestrelli et al., 1999 ). Reduced visualization is associated with this technique, however, and its application to pediatrics remains uncertain ( Lukban et al., 2000 ).
▪ INGUINAL HERNIORRHAPHY AND UMBILICAL HERNIORRHAPHY
During the seventh month of gestation, the testicle descends from the abdomen through the inguinal wall into the scrotum. The processus vaginalis, a peritoneal covering, encloses the testicles during their descent. In term infants, the processus vaginalis is usually closed at birth, but it remains patent in 15% to 37% of people. In premature infants, the incidence is much higher depending on the gestational age at the time of birth. The continued patency of the processus vaginalis is the principal factor in the development of congenital hernias and hydroceles.
Inguinal hernia repair is the most frequent general surgical procedure performed by pediatric surgeons. Males are more frequently affected than females, and the incidence of inguinal hernia is highest in the first year of life. Right-sided hernias (60%) occur more frequently than left-sided (30%) and bilateral (10%) hernias. Other risk factors associated with inguinal hernias are prematurity, chronic respiratory illness, and excessive intraperitoneal fluid (ventriculoperitoneal shunts, ascites, peritoneal dialysis).
The surgical technique for this procedure is well described ( Rowe and Lloyd, 1986 ). Laparoscopic techniques have also been described ( Lobe and Schropp, 1992 ; Lee and Liang, 2002 ; Schier et al., 2002), as well as needleoscopic techniques ( Prasad et al., 2003 ). The overall complication rate after elective hernia repair is about 2% and increases to 14% after operations for incarcerated hernia. A major surgical issue in patients with a unilateral inguinal hernia is whether the contralateral side should be explored, thereby subjecting the patient to possible unnecessary damage to the contralateral vas deferens and spermatic cord. In a number of studies, a patent contralateral processus vaginalis occurs about 60% of the time. However, this patency appears age related, with the highest rate occurring in infants (63%) and incidence decreasing until 2 years of age, when it appears to plateau at 41% ( Rowe and Lloyd, 1986 ). Despite the high incidence of patent processus vaginalis, the incidence of contralateral hernias is about 15%. The development of a contralateral hernia is also age dependent. If the initial hernia developed in the first year of life, there is a fourfold greater chance that a contralateral hernia will develop compared with children whose initial hernia presented after 1 year of age. In girls with unilateral inguinal hernias, the incidence of positive explorations for contralateral hernias is 60%. Consequently, girls almost always undergo contralateral exploration. Laparoscopy without a separate incision has been advocated to examine the contralateral side when the ipsilateral hernia sac is of sufficient width to allow passage of a laparoscope ( Yerkes et al., 1998 ).
Herniorrhaphies are commonly performed as elective procedures; however, in children with incarceration and signs of bowel obstruction, a rapid-sequence induction with application of cricoid pressure is needed.
The following discussion pertains to elective, uncomplicated hernias. Anesthesia can be induced by mask inhalation of volatile agents or by rectal or intravenous techniques. Endotracheal intubation is usually unnecessary for herniorrhaphy except in infants under 1 year of age, in whom it may be difficult to maintain an adequate airway with bag and mask ventilation without distending the stomach. However, the use of the LMA in these patients may make tracheal intubation unnecessary. The patient must be well anesthetized when the spermatic cord is being manipulated. Inadequate depth of anesthesia at this stage can result in laryngospasm and/or bradycardia. Caudal epidural anesthesia or ilioinguinal/iliohypogastric nerve block can be quite effective both in providing postoperative pain relief and in diminishing the intraoperative anesthetic requirements ( Markham et al., 1986 ). Premature infants have a particularly high incidence of inguinal hernias. In these infants, in whom an inhalation anesthetic may have increased risks, spinal anesthesia ( Harnik et al., 1986 ) and caudal epidural ( Spear et al., 1988 ) anesthesia have been used successfully to avoid general anesthesia and endotracheal intubation.
▪ ORCHIOPEXY
Cryptorchidism affects approximately 0.8% of 1-year-old boys. The undescended testicle may lie within the abdomen, the inguinal canal, or the external ring just proximal to the scrotum. Although the undescended testicle is usually associated with a hernia, the most significant medical risk for the patient is the chance of developing a malignancy, which is 10-fold greater than in a normally descended one.
The objectives of repair for undescended testicles are to alter the course of the spermatic artery from the renal pedicle to the internal ring to the external ring and to create in its place a direct line from the renal pedicle to the scrotum. However, the surgical approach to patients with undescended testes is not uniform ( Hinman, 1987 ; Heiss et al., 1992) . The general approach to patients with a nonpalpable testis is inguinal exploration. If neither the testis nor proof of its absence is found, the lower posterolateral surface of the peritoneal cavity is explored. When the testis is found, it is either removed or surgically placed in the scrotum. This can be accomplished by a staged orchiopexy, autotransplantation of the testis, or Fowler-Stephens procedure. The Fowler-Stephens approach takes advantage of the vascular arcades between the deferential and spermatic arteries within the cord. Because of this collateral blood flow, high ligation of the testicular vessels can preserve the testicular blood supply andprovide the surgeon with mobility in bringing the testicle down into the scrotum. The Fowler-Stephens approach has undergone modification and is now generally done in two stages. The first stage involves clipping of the spermatic vessel, whereas the second stage, performed months later, involves the formal orchiopexy. With the advent of laparoscopic surgery, both stages of the Fowler-Stephens approach can be done with the aid of a laparoscope ( Atlas and Stone, 1992 ; Bogaert et al., 1993 ).
The anesthetic considerations are similar to those for inguinal hernia repair. Because of the traction and manipulation of the spermatic cord and testicle, the incidence of intraoperative bradycardia and laryngospasm is somewhat increased. Consequently, a deeper level of anesthesia is required. However, the need for a deeper plane of anesthesia and the risk of bradycardia and laryngospasm can be lessened by the use of intraoperative nerve blocks or regional anesthesia. If an intra-abdominal exploration or the use of laparoscopy is anticipated, or both, the trachea is generally intubated. Because the incidence of postoperative nausea and pain is significant, caudal nerve blocks and prophylactic antiemetics, such as ondansetron, 0.1 mg/kg, are recommended.
▪ SURGERY FOR PYLORIC STENOSIS
Pyloric stenosis is one of the most common gastrointestinal abnormalities presenting in the first 6 months of life. This disorder has a polygenic mode of inheritance and occurs 4 times more commonly in males and more frequently in white infants. The frequency of this disorder ranges from 1.4 to 8.8:1000 live births ( Zeidan et al., 1988 ; Dubé et al., 1990 ; Saunders and Williams, 1990 ; Bissonnette and Sullivan, 1991 ; Murtagh et al., 1992 ). There is some controversy regarding the associated risk of pyloric stenosis with the maternal postnatal exposure to macrolides ( Louik et al., 2002 ; Sorensen et al., 2003 ). Pyloric stenosis has been associated with cleft palate and esophageal reflux.
The cardinal features of pyloric stenosis condition are projectile vomiting, visible peristalsis, and a hypochloremic, hypokalemic, metabolic alkalosis. Although hypokalemia is a frequent finding, Schwartz and others (2003) reported in a retrospective chart review that 36% of patients with pyloric stenosis were noted to have hyperkalemia. Nonbilious vomiting is the classic presenting symptom and generally occurs between 2 and 8 weeks of age. Jaundice occurs in less than 5% of patients and is thought to be associated with caloric deprivation and hepatic gluconyltransferase deficiency. The jaundice resolves after successful treatment. Diagnosis is made by palpation of an olive-sized mass in the upper abdomen and is frequently confirmed by radiographic studies. Although false-positive studies are rare, false-negative findings can occur in up to 19% of the ultrasound examinations and in 10% of the contrast studies.
The pathologic condition involves gross thickening of the circular muscles of the pylorus, resulting in a gradual obstruction of the gastric outlets. Vanderwinden and others (1992) noted a deficiency of nitric oxide synthetase in the muscle layers of infants with pyloric stenosis. The pathophysiology of pyloric stenosis frequently leads to hypovolemia and a hypochloremic metabolic alkalosis.
Winters (1973) outlines the pathophysiology that leads to hypochloremic, hypokalemic metabolic alkalosis. In pyloric stenosis, persistent vomiting results in a loss of gastric juices rich in hydrogen and chloride ions and, to a lesser extent, sodium and potassium ions. Because the obstruction is at the level of the pylorus, the vomitus does not contain the usual alkaline secretions of the small intestine; the patient develops a metabolic alkalosis.
As an increased bicarbonate load is presented to the kidney, the resorptive capacity of the proximal tubule is overwhelmed and an increased amount of NaHCO3 and water is delivered to the distal tubule. Because NaHCO3 cannot be reabsorbed in the distal tubule, aldosterone secretion occurs. Increased aldosterone increases sodium reabsorption and kaliuresis. Potassium loss is further exacerbated by potassium being exchanged in the tubule for hydrogen in an effort to maintain normal plasma pH.
With persistent vomiting and intravascular volume depletion, the renal response shifts to maintain the patient's intravascular volume and sodium conservation occurs. Increased secretion of aldosterone promotes sodium conservation and potassium excretion. In the distal tubule, sodium is also conserved in exchange for hydrogen ions. This may result in a paradoxical aciduria and worsening metabolic alkalosis.
Surgical pyloromyotomy, a relatively simple procedure in the hands of skilled pediatric surgeons, is curative ( Fig. 19-3 ). The operative mortality of 10% has declined to less than 0.5%. The surgery can be performed either laparoscopically or as an open procedure. In a comparative study, Campbell and others (2002) noted that laparoscopic pyloromyotomy has become the dominant approach. However, laparoscopic pyloromyotomy is associated with an increased rate of complications, higher hospital charges, and a reduction in the general surgical resident's operating experience ( Campbell et al., 2002 ). Pyloromyotomy for pyloric stenosis is not a medical emergency that requires immediate surgical intervention. The major anesthetic considerations are recognizing and treating dehydration and acid-base abnormalities before beginning anesthesia. In addition, the patient is at risk for aspirating gastric contents.
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FIGURE 19-3 Pyloric stenosis. Operative technique of pyloromyotomy. A, Incision made on anterosuperior surface through avascular area. B, Cross section of hypertrophied pylorus after operation has been completed. C, Circular muscle is separated, allowing submucosa to bulge. (From Benson CO: Infantile hypertrophic pyloric stenosis. In Welch KJ, et al., editors: Pediatric surgery, 4th ed. Chicago, 1986, Year Book Medical Publishers.) |
The initial therapeutic approach is aimed at repletion of intravascular volume and correction of electrolyte and acid-base abnormalities (e.g., 5% dextrose in 0.45% NaCl with 40 mmol/L of potassium infused at 3 L/m2 per 24 hr). Most children respond to therapy within 12 to 48 hours, after which surgical correction can proceed in a nonemergency manner.
Once the child is satisfactorily hydrated and after the appropriate monitors (precordial stethoscope, electrocardiogram, pulse oximeter, and blood pressure cuff) are placed, the infant is ready for induction of anesthesia. The obstructed pylorus and associated vomiting increase the possibility of aspirating gastric contents during induction of anesthesia. A thorough evacuation of the stomach contents through a nasogastric or an orogastric tube, with proper preoxygenation and monitoring, greatly reduces the chance of regurgitation during induction, although it does not completely eliminate the possibility of aspiration ( Cook-Sather et al., 1997 ). Infants with pyloric stenosis are thus considered by some anesthesiologists to be in an equivalent status to infants with a full stomach. Thus, a rapid sequence induction is preferred to secure the airway and minimize the risks of aspiration ( Dierdorf and Krishna, 1981 ; Battersby et al., 1984 ). On the other hand, mask inhalation induction preceded by careful emptying of the stomach has been used safely in several pediatric centers ( MacDonald et al., 1987 ). In a prospective nonrandomized observational study of 76 infants with pyloric stenosis, Cook-Sather and others (1998) compared three techniques: awake intubation, rapid sequence intubation, and modified rapid sequence intubation (ventilation through cricoid pressure). In this study, awake intubation was not superior to anesthetized, paralyzed intubations. Awake intubation prevented neither bradycardia nor oxygen desaturations.
After induction and intubation of the trachea, a nasogastric or an orogastric tube is reinserted and left in place during the operative procedure. This allows the surgeon to test the integrity of the pyloric mucosa after pyloromyotomy. A small volume of air is injected down the nasogastric tube, and the surgeon manipulates the air bubble into the duodenum and occludes the bowel lumen both proximal and distal to the incision. Mucosal perforation is indicated if there is air leakage. After the operation, which usually requires less than 30 minutes, the effects of any nondepolarizing muscle relaxant are reversed. Then the infant can be safely extubated when fully awake and with intact protective airway reflexes. Some believe that opioid analgesia is seldom necessary ( Battersby et al., 1984 ) and may predispose patients to a prolonged emergence from anesthesia ( MacDonald et al., 1987 ). It is not unusual to encounter lethargy or drowsiness in these infants in the immediate postoperative period. Respiratory depression has been noted to occur postoperatively and is possibly related to cerebrospinal fluid pH and hyperventilation ( Andropoulos et al., 1994 ). Rare occurrences of hypoglycemia, apnea, convulsions, and cardiac arrest in the early postoperative period have also been cited. These events have been ascribed to the cessation of intravenous glucose infusions and the depletion of liver glycogen in these infants ( Shumake, 1975 ). Infants usually begin oral feedings 8 hours after the procedure. The choice of maintenance anesthetic agent for infants with pyloric stenosis has been studied ( Wolf et al., 1996 ; Chipps et al., 1999 ; Davis et al., 2001 ; Galinkin et al., 2001 ).
In the study by Wolf and others, clinical postoperative apnea occurred in 3 of 11 infants anesthetized with isoflurane and in none of the 9 infants anesthetized with desflurane. In a multicenter study comparing halothane and remifentanil, where both drugs were administered to similar clinical end points, remifentanil was not associated with postoperative respiratory depression. In this study, all infants received both preoperative and postoperative pneumograms, and remifentanil (as opposed to halothane) was not associated with new pneumogram abnormalities in the postoperative period ( Davis et al., 2001 ; Galinkin et al., 2001 ).
▪ WILMS TUMOR PROCEDURES
Wilms tumor is the most common childhood abdominal malignancy, occurring in an incidence, consistent throughout the world, of 5.0 to 7.8 per 1 million children under 15 years of age. Wilms tumor accounts for about 6% of all malignancies in childhood. The incidence is equal in the two sexes. The peak age at diagnosis is between 1 and 3 years. Wilms tumor occurs bilaterally in 5% of patients. Patients with Wilms tumor frequently have associated anomalies (aniridia, 1%; hemihypertrophy, 2%; genitourinary abnormalities, 5%; ectopic and solitary kidneys [horseshoe kidneys, ureteral duplications, hypospadias]). Other associated conditions include Beckwith-Wiedemann syndrome and neurofibromatosis. The signs and symptoms associated with Wilms tumor are variable. The most frequent finding is an increasing abdominal girth with a palpable abdominal mass (85%). Hypertension occurs in 60% of patients, and hematuria is present in 10% to 25%.
Wilms tumor generally is located in the upper or lower renal pole. It may involve the renal vein and extend up the vena cava to the right atrium. Prognosis of the disease is related to its staging ( Table 19-1). Patients with favorable staging have an 80% to 90% chance of cure, whereas patients with metastasis have a 50% chance of long-term survival. Risk factors for local recurrence of Wilms tumor include an advanced local stage (involvement of the para-aortic lymph nodes), unfavorable histology, and spillage of tumor at the time of resection ( Shamberger et al., 1999 ). Therapy for Wilms tumor includes surgery, chemotherapy, and radiotherapy. Depending on the size of the tumor and the staging, chemotherapy may be started either before or after surgery. Chemotherapy generally involves vincristine, actinomycin, and anthracycline (doxorubicin).
TABLE 19-1 -- Wilms tumor staging
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Staging |
Description |
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I |
Tumor limited to the kidney and excised. |
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II |
Tumor extending beyond the kidney, but completely excised. The tumor may have been biopsied or there may have been local spillage of tumor confined to the flank. |
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III |
Residual nonhematogenous tumor confined to the abdomen. Lymph node involvement in the abdomen. Diffuse peritoneal contamination by spillage or tumor growth that has penetrated through the peritoneal surface. |
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IV |
Hematogenous metastases. Lymph node involvement beyond the abdominal cavity. |
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V |
Bilateral renal involvement at diagnosis. |
Preoperative evaluation of the patient is related to the presence of metastases and the patient's cardiopulmonary function. If the patient has had prior chemotherapy with Adriamycin, cardiac function should be assessed by echocardiogram (see Chapters 3 and 32 , Cardiovascular Physiology and Systemic Disorders). Serum electrolyte levels should be assessed if there is a history of vomiting. Renal dysfunction is unusual even in patients with bilateral Wilms tumor.
Anesthetic considerations revolve around the issue of abdominal distention with delayed gastric emptying and potentially large intraoperative blood losses. Abdominal distention may place the patient at risk for aspiration of gastric contents, so full-stomach precautions should be taken at the induction of anesthesia. Intraoperative blood loss can be a significant factor because of the tumor's location and possible involvement of the renal vein and vena cava. Two large-bore intravenous catheters are recommended. Because of the possibility that the vena cava may be cross-clamped (either to be explored for extension of tumor or to control hemorrhage), the large-bore catheters should be preferentially inserted above the diaphragm.
Pulmonary function may be compromised because of metastasis, tumor embolization, abdominal distention, or surgical traction. Monitoring of the patient should include pulse oximetry and capnography as well as the standard monitors of electrocardiograph, blood pressure, and esophageal stethoscope. Arterial catheters are generally reserved for patients with large tumors, patients with previous intra-abdominal surgery (increased number of adhesions), and patients with significant cardiorespiratory depression.
After induction, anesthesia is maintained with potent inhalation anesthetic agents. Nitrous oxide is avoided because of the bowel distention, and opioids are administered to reduce the anesthetic requirements. An alternative approach that provides both excellent operative conditions and postoperative pain control is the use of combined general anesthesia with a continuous epidural infusion.
▪ NEUROBLASTOMA PROCEDURES
Neuroblastoma is the most common extracranial solid tumor of childhood and involves the postganglionic sympathetic nervous system. Fifty percent of tumors arise in the adrenal, 30% occur below the diaphragm, and 20% occur in cervical or thoracic sites. Neuroblastoma accounts for 8% to 10% of pediatric cancers. The median age of presentation is 22 months, with 37% of patients presenting under 1 year of age, and 51% of patients being less than 4 years of age. Clinical presentation may be related to the primary tumor, to its metastasis, or to the associated paraneoplastic syndromes ( Table 19-2 ). Metastases from neuroblastoma occur in lymph nodes, liver, cortical bone, bone marrow, orbits, and skin. The paraneoplastic syndromes can present with hypertension secondary to catecholamine release and/or kidney displacement with renal artery stretching and renin-angiotensin stimulus. The gastrointestinal symptoms (diarrhea, flushing, abdominal distention) are attributed to vasoactive intestinal peptides, whereas the etiology of opsoclonus and ataxia is unclear.
TABLE 19-2 -- Presenting signs and symptoms of neuroblastoma
|
Primary tumor |
Abdominal mass or pain; respiratory distress or dysphagia; vocal cord paralysis; bowel or bladder dysfunction; Horner's syndrome; heterochromia of iris on affected side; incidental finding on chest radiograph |
|||||||||
|
Metastatic disease |
Hepatomegaly; lymphadenopathy; bone pain; periorbital ecchymoses; subcutaneous nodules; marrow replacement with anemia, fever, or bruising from low blood counts; systemic illness; failure to thrive; fever of unknown origin |
|||||||||
|
Paraneoplastic syndromes |
|
Tumor prognosis has been related to age of presentation, extent of disease (staging) ( Fig. 19-4 ), degree of tumor differentiation, amount of catecholamine metabolites, serum ferritin level, lactate dehydrogenase level, neuron-specific enolase level, serum lymphocyte count, ganglioside presence, N-myc amplification, deletion of chromosome 1p, additional copies of chromosome 17q, and TRKA expression ( Smith et al., 1989 ; Hiyama et al., 1991 ; Berthold et al., 1992 ; Eckschlager, 1992 ; Murakami et al., 1992 ; Qualman et al., 1992 ; Shuster et al., 1992 ; Haase et al., 1999 ). However, patient age and tumor stage are the two most important independent variables. The Evans staging system uses tumor location, lymph node involvement, and presence of metastases, whereas the Pediatric Oncology Group (POG) system emphasizes tumor resectability and identification of residual disease to predict survival and treatment.
|
FIGURE 19-4 Prognosis of neuroblastoma related to age and staging. A, Children under 1 year of age. B, Children over 1 year of age. The staging is according to the Pediatric Oncology Group (POG) system. Stage A: Complete gross resection of primary tumor, with or without microscopic residual. Intracavitary lymph nodes, not adhered to and removed with primary (nodes adhered to or within tumor resection may be positive for tumor without upstaging patient to stage C), histologically free of tumor. If primary in abdomen or pelvis, liver histologically free of tumor. Stage B: Grossly unresected primary tumor. Nodes and liver are the same as for stage A. Stage C: Complete or incomplete resection of primary. Intracavitary nodes not adhered to primary histologically positive for tumor. Liver as in stage A.Stage D: Any dissemination of disease beyond intracavitary nodes: extracavitary nodes, liver, skin, bone marrow, bone. Stage D(S): Would be Evans stage I or II except for metastatic tumor in liver, bone marrow, or skin. Evans stage I: Tumor confined to the organ of structure of origin. Evans stage II: Tumor extending in continuity beyond the organ or structure of origin but not crossing the mid-line. Regional lymph nodes on the ipsilateral side may be involved. (Data courtesy of Dr. Jonathan J. Shuster and the Pediatric Oncology Group. From Brodeur GM: Neuroblastoma and other peripheral neuroectodermal tumors. In Fernbach DJ, Viett TJ, editors: Clinical pediatric oncology, St. Louis, 1991, Mosby.) |
Treatment involves surgical resection and chemotherapy. Although neuroblastoma is radiosensitive, 45% of patients present with metastasis so that its use is sometimes limited in primary therapy. In a series of adrenal neuroblastomas less than 6 cm not associated with adjacent vessel or organ involvement, De Laagause and others (2003) reported successful tumor removal with laparoscopic techniques. The anesthetic considerations depend on the planned surgical procedure, the location and size of the tumor, and the metabolic effects of the tumor. Electrolyte imbalance may result from vomiting and diarrhea caused by excessive production of vasoactive intestinal peptide (VIP). Despite the production of catecholamines, significant hypertension has been reported in 9% to 30% of patients ( Weinblatt et al., 1983 ;Haberkern et al., 1992 ).
Intraoperatively, blood loss and third-space fluid losses can accompany the resection of tumor. Haberkern and others (1992) noted in a retrospective review that 45% of patients had hypotension after the tumor excision, whereas fewer than 3% of the patients had cardiovascular signs of increased catecholamine release during tumor resection. Although in patients with mediastinal neuroblastoma airway complications are rare owing to the tumor's location in the posterior mediastinum, airway compromise can occur, and evidence of airway compression by the tumor should be evaluated before starting the anesthetic induction. Intravenous or inhalational inductions may be performed. Both volatile agents and opioids have been safely used along with combined regional and general anesthetic techniques (Haberkern et al., 1992 ).
▪ ANTIGASTROESOPHAGEAL REFLUX PROCEDURES
Gastroesophageal reflux (GER) involves a dysfunction of the esophageal sphincter mechanism that allows gastric contents to return into the esophagus and consequently may place an anesthetized patient at risk for aspiration. The clinical spectrum of GER can range from patients who are completely asymptomatic to patients with severe esophagitis, esophageal bleeding, esophageal stricture, malnutrition, and respiratory compromise. Although in the pediatric population GER can be physiologic secondary to an immature maturation of the lower esophageal sphincter mechanism, this aspect of GER generally resolves by 15 months of age. GER is also seen in children who are neurologically compromised as well as patients who have survived diaphragmatic hernias, tracheoesophageal fistula, and esophageal atresia repairs. GER has also been noted in about 10% of patients who have undergone successful treatment of pyloric stenosis.
In normal children, reflux of gastric contents is prevented by the gastroesophageal junction. This junction is composed of a lower esophageal sphincter (LES). The LES is a high-pressure zone in the distal esophagus that lies in both the mediastinum and abdomen and becomes functionally mature by 6 weeks of postnatal age. Factors that affect the valve mechanism of the LES include the cardioesophageal angle of His; the esophageal hiatus, a sling of muscle that is part of the diaphragm; and the phrenoesophageal ligament. The degree of reflux, the duration of acid exposure within the esophagus, the ability of the esophagus to clear its contents, and the extent of mucosal damage are the primary factors that determine the degree of esophagitis and consequently its clinical and pathologic significance.
In pediatric patients, the complications of GER include respiratory compromise (bronchospasm, chronic aspiration with pneumonitis, reactive airway disease and apnea) and esophagitis (esophageal metaplasia, Barrett's esophagus, stricture, dysphagia). Diagnostic evaluation includes an upper gastrointestinal series, nuclear scan, upper endoscopy, and esophageal pH probe.
Treatment of GER may involve both medical and surgical therapies. Medical therapy consists of both conservative and pharmacologic interventions (thickened feedings, avoidance of overfeeding, postcibal position therapy). The use of medication is aimed at blocking acid secretions using H2-blocker agents (e.g., ranitidine) and improving gastroesophageal motility and gastric emptying (e.g., metoclopramide, bethanechol). Cisapride, a dopamine antagonist, is also used as a motility drug. Its mode of action is postulated to increase the release of acetylcholine from the myenteric plexus and to increase receptor sensitivity to acetylcholine.
The surgical procedures are aimed at establishing an intra-abdominal segment of esophagus and creating a physiologic angle of His ( Fig. 19-5 ). The two common procedures are the 360-degree fundoplication of Nissen and the partial wrap of Thal-Nissen. To avoid the gas bloat syndrome (aerophagia, gastric distention, inability to belch or vomit) associated with Nissen fundoplications, the Thal-Nissen partial wrap is frequently used.
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FIGURE 19-5 A, Salient features of Nissen fundoplication in infants. A, Crural sutures to reduce hiatus. B, Generous loose, adequate tissue in the wrap. C, Sutures placed through seromuscular depth of both gastric and esophageal walls. D, Sutures to fix the fundus to the diaphragm. E, Appropriately sized mercury-filled dilator to ensure adequate lumen. F, Gastrostomy in all infants and whenever there is any question of gastric outlet problems. B, The Thal fundoplication. A partial wrap of the fundus is performed anteriorly around the lower esophageal segment. (A from Randolph JG: Ann Surg 198:579, 1983. Illustrated by Peter Stone. B from Ashcraft KW: Thal fundoplication. In Ashcraft KW, Holder TM, editors: Pediatric esophageal surgery. Orlando, 1986, Grune & Stratton, Inc.) |
The surgical procedure can be performed as either an open or a laparoscopic procedure ( Georgeson, 1993 ; Rothenberg, 1998 ; Bourne et al., 2003 ; Esposito et al., 2003 ; Steyaert et al., 2003 ). In the children undergoing laparoscopic antireflux procedures, the physiological perturbations of pneumoperitoneum, increased intra-abdominal pressure, and the associated absorption of carbon dioxide need to be considered.
Surgical success rates approach 95% in pediatric patients with normal neurologic development, but in children who are neurologically impaired, morbidity and mortality remain high. It is important in these patients to determine if their underlying symptoms result from GER as opposed to nasopharyngeal incoordination and/or esophageal or antral dysmotility ( Flake et al., 1991 ; Martinez et al., 1992 ; Smith et al., 1992 ). The presence of GER places the patient at risk for aspiration during induction of anesthesia. Preoperative preparation with H2-blockers and motility drugs should be continued. A rapid sequenceinduction should be used, providing a difficult airway is not anticipated. At least one large-bore intravenous catheter should be placed, although fluid and blood losses are minimal. However, pneumothorax, lacerated spleen, puncture or compression of the vena cava or aorta, and lacerated hepatic veins can occur.
Other anesthesia concerns in patients with GER focus on the degree of neurologic and respiratory compromise of the patient. Because these children frequently have seizure disorders, preoperative concern should be directed at proper anticonvulsant therapy. Oral anticonvulsants generally cannot be administered for 48 to 72 hours in the postoperative period. Consequently, patients requiring carbamazepine and valproic acid need alternate medicines so that breakthrough seizures do not occur.
For children with severe respiratory compromise or neuromuscular disease, postoperative ventilatory support may be necessary. In children without significant preoperative pulmonary compromise, extubation may be delayed after surgery and supplemental oxygen is given as needed.
▪ SURGERY FOR BILIARY ATRESIA
Biliary atresia is characterized by a lack of gross patency of the extrahepatic bile duct. It occurs in 1:15,000 live births ( Shim et al., 1974 ), and in 10% to 15% of the patients, other abnormalities are associated with embryologic development, including absent inferior vena cava, intestinal malrotation, polysplenia, and preduodenal portal vein ( Lilly and Chandra, 1974 ). Although biliary atresia is often considered a congenital lesion, it has dynamic properties as well. In microscopic studies of the biliary anatomy obtained from patients at 2 and 4 months of age, the histologic results suggest that biliary structures gradually disappear and are replaced by fibrous tissue. In addition, the success rate for the palliative surgical procedure has been reported as 50% in infants operated on before 4 months of age and 80% in those undergoing surgery before 2 months of age ( Ohi et al., 1985 ).
Kasai and others (1989) , in a review of 245 patients undergoing corrective procedures over a 35-year period, noted that 10-year survival was 74% in infants operated on before 60 days of life. However, Tan and others (1994) have questioned whether earlier corrective surgery is associated with ductal patency. In a series of 205 patients, Tan and others noted that survival may be more closely related to the severity of intrahepatic biliary cholangiopathy.
In a 27-year review of 81 patients with biliary atresia, Wildhaber and others (2003) noted that direct bilirubin less than 2.0, the absence of bridging liver fibrosis, and the number of cholangitis episodes were predictive factors in the success of the Kasai portoenterostomy. Popovic and others (2003) noted that cholinesterase levels can be a useful index of liver function (protein synthesis) early after the Kasai procedure and is independent of albumin synthesis.
Clinically, biliary atresia presents in infants from 1 to 6 weeks of age. About 50% are anicteric until the second or third week of life. The diagnosis of biliary atresia is confirmed either by liver biopsy or by exploratory laparotomy. Surgical palliation for biliary atresia involves hepatic portoenterostomy (Kasai procedure) ( Fig. 19-6 ).
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FIGURE 19-6 Illustrations of the Kasai procedure and its various modifications. A, Original Kasai. B, Kasai H-double-barreled vent. C, “Bishop-Koop” vent. D, Gallbladder “Kasai.” (From Filston HC, Izant RJ Jr: The surgical neonate, evaluation, and care. Norwalk, CT, 1985, Appleton-Century-Crofts.) |
Complications of the surgical repair and from the underlying disease state include cholangitis, portal hypertension, and fat-soluble vitamin deficiency ( Kasai et al., 1975 ). For the anesthesiologist, these complications take on greater significance in patients who return to the operating room for further surgical revision of biliary drainage, treatment of intra-abdominal sepsis, or relief of an intestinal obstruction. Because these complications occur frequently and because end-stage liver disease can follow the Kasai procedure, the role of liver transplantation as a primary treatment of biliary atresia has been raised. Kasai and others (1989) suggested that liver transplantation as a primary form of treatment may be indicated for patients older than 3 months with an enlarged, hard liver. Laurent and others (1990) noted that although Kasai's operation does improve the prognosis of biliary atresia, it is not a definitive cure and 80% of these patients become candidates for liver transplantation.
Anesthetic management for a Kasai procedure ( Kasai, 1974 ) in patients with biliary atresia follows the basic principles of pediatric anesthesia. In infants in whom venous access is already present, induction is achieved with a hypnotic agent, such as propofol (2 to 3 mg/kg), and a muscle relaxant (cisatracurium 0.2 mg/kg). In infants without an intravenous catheter in place, inhalation induction is performed with oxygen, nitrous oxide, and sevoflurane. Once the child is adequately anesthetized, an intravenous catheter is inserted and a muscle relaxant is administered to facilitate endotracheal intubation and to decrease the concentration of potent inhalation anesthetic. After induction, anesthesia is maintained with an oxygen-air-isoflurane mixture along with intravenous opioids. Because of bowel distention, nitrous oxide is avoided.
Gelman and others (1984) have shown that hepatic blood flow and oxygen supply are better maintained during isoflurane than during halothane anesthesia. Consequently, isoflurane in an oxygen and air mixture is most commonly administered to patients undergoing surgery for biliary atresia.
Anesthesia monitoring for the patient undergoing a Kasai procedure is similar to that used for other pediatric surgical procedures. Arterial cannulation and central venous pressure monitors are rarely used and are generally reserved for patients with other coexisting problems, such as sepsis, pneumonia, cholangitis, and severe cirrhosis. In general, hemodynamic stability is well maintained and the need for intraoperative vasoactive agents is rare. Sometimes the surgical approach involves dividing the triangular and coronary ligaments and displacing the whole liver anteriorly. Although this technique may facilitate exposure, it may compress the inferior vena cava and thereby result in hypotension by decreasing venous return. Ventilation is controlled, and end-tidal gases are monitored for carbon dioxide, oxygen, and volatile anesthetic agents. Adequacy of oxygenation is monitored by the pulse oximeter.
The operative procedures generally last 3 to 4 hours, and major blood loss does not occur. Perioperative fluid therapy involves replacement of maintenance and deficit fluids as well as provision for the calculated third-space losses. Third-space losses may vary from 6 to 10 mL/kg per hr. Generally, lactated Ringer's solution is used to restore third-space losses.
Prevention of hypothermia is a major concern for the anesthesiologist. The large surface-to-volume ratio of infants, their relative lack of insulation tissue, coupled with the cold operating room, exposure of body cavities to low environmental temperatures, infusions of cold fluid, and ventilation with dry gases, all increase the potential for hypothermia during surgery. Consequently, great effort must be applied both before and during surgery to protect against heat loss. Methods of preventing heat loss are discussed in Chapter 5 , Thermoregulation: Physiology and Perioperative Disturbances.
The pharmacology of anesthetic agents in infants and children with hepatic disease has not been fully evaluated. Although the liver is the major site of drug biotransformation, the effects of hepatic dysfunction on drug elimination and disposition are inconsistent. The degree of liver dysfunction and the drug's ability to bind to plasma proteins are important variables in determining drug kinetics in patients with liver disease.
In general, liver function is fairly well preserved in the first few months of life in children with biliary atresia. As the children get older and ductal fibrosis begins, liver dysfunction ensues. Consequently, in children who return for repeat surgical procedures, the pharmacology of intravenous anesthetic agents and adjuncts may be altered.
In infants with biliary atresia undergoing the Kasai procedure, if major fluid shifts have not occurred, blood loss has been minimal, and the patient is warm, all efforts are made to reverse the muscle relaxation and extubate the trachea at the end of the procedure. In children with other organ system failures (specifically sepsis, cholangitis, or pneumonia), those who are cold at the end of the procedure (<35°C), or those who have undergone transfusion of more than one blood volume, extubation is delayed until warmth and hemodynamic stability are restored. In these children, postoperative recovery and monitoring are carried out in an intensive care setting.
▪ LIVER TUMOR PROCEDURES
Liver tumors in children are uncommon, but malignant tumors comprise 72% of pediatric primary hepatic tumors. Of these malignant tumors, hepatoblastoma and hepatocarcinoma are the predominant tissue types ( Table 19-3 ). Hepatoblastoma commonly affects white boys under 2 years of age. An abdominal mass that has increased in size is usually the presenting symptom. Anemia, jaundice, and ascites are infrequent findings. Liver function test results are frequently normal. From 2% to 3% of patients may have an associated hemihypertrophy ( Geiser et al., 1970 ). Hepatoblastoma has also been associated with isosexual precocity as a result of the liver's ectopic gonadotropic production and the Beckwith-Wiedemann syndrome ( Sotelo-Avita et al., 1976 ), polyposis coli, Wilms tumor, and fetal alcohol syndrome.
TABLE 19-3 -- Malignant hepatic tumors
|
Hepatomas |
Hepatoblastoma |
129 |
|
Hepatocellular carcinoma |
98 |
|
|
Other |
Mixed mesenchymal tumor |
9 |
|
Rhabdomyosarcoma |
6 |
|
|
Angiosarcoma |
4 |
|
|
Undifferentiated sarcoma |
3 |
|
|
Teratocarcinoma |
1 |
|
|
Cholangiosarcoma |
1 |
|
|
Malignant histiocytoma |
1 |
From Exelby PR, Filler RM, Grosfeld JL: Liver tumors in children in the particular reference to hepatoblastoma and hepatocellular carcinoma: American Academy of Pediatrics Surgical Section Survey—1974. J Pediatr Surg 10:329, 1975.
An increased incidence of hepatoblastomas has been associated with low birth weight ( Ikeda et al. 1997 ; Feusner et al., 1998 ). Between 1973 and 1997, the rate of hepatoblastoma increased. This is in contrast to the decreased incidence observed for hepatocarcinoma ( Darbari et al., 2003 ). Hepatoblastomas are derived from primitive epithelial parenchyma and are classified by the predominant epithelial component. Among the variants are fetal, embryonal, macrotrabecular, and anaplastic. Survival is related to the histology and completeness of the surgical resection. Fetal histology has a greater than 90% survival rate compared with a 50% survival rate for embryonal histology. A few survivors have anaplastic histology.
Hepatocellular carcinoma appears to have two age peaks: under 4 years of age and between 12 and 15 years of age ( Leventhal, 1987 ). As in adults with hepatocellular carcinoma, the prognosis of survival in children with the disease is 5% to 10%. Typically, patients with hepatocellular carcinoma have the systemic symptoms of weight loss, jaundice, fever, and lethargy. As opposed to adults with this tumor, only about 5% of children have associated cirrhosis ( Jones, 1960 ). Other associated diseases include von Gierke's disease, type I glycogenesis, cystinosis, extrahepatic biliary atresia, α1-antitrypsin deficiency, hypoplasia of intrahepatic bile ducts, Wilson's disease, giant cell hepatitis, and Solo's syndrome ( Zangeneh et al., 1969 ; Palmer and Wolfe, 1976 ; Weinberg et al., 1976 ; Dehner, 1978 ).
Anesthetic management for pediatric patients undergoing hepatic lobe resection or tumor resection involves the same principles as for patients with biliary atresia. Efforts at maintaining adequate alveolar ventilation, temperature homeostasis, cardiovascular stability, and fluid management have previously been described. Some patients receive adjunct chemotherapy before surgery. The chemotherapeutic protocol must be reviewed. Frequently, Adriamycin, an anthracycline, is a major component of hepatic cancer chemotherapy and has been associated with a dose-dependent irreversible cardiomyopathy. All patients receiving anthracycline chemotherapy should undergo history, physical examination, electrocardiogram, chest radiograph, and echocardiogram to further evaluate signs and symptoms of cardiac toxicity and cardiac reserve (see Chapters 3 and 32 , Cardiovascular Physiology and Systemic Disorders).
Because the potential for massive blood loss exists in patients undergoing hepatic resection, adequate venous access and invasive monitoring are essential to patient management. Two or three large-bore peripheral intravenous catheters are inserted, and a central venous pressure catheter is placed to monitor cardiac filling pressures. Either the radial or the femoral artery is cannulated, not only to monitor blood pressure but also to determine blood gas levels, chemistry, and coagulation profile. Because of the potential for large fluid shifts, a Foley catheter is placed to measure urine output and assist in assessing the adequacy of fluid resuscitation.
Massive blood volume replacement is a frequent component of the anesthetic resuscitation in children undergoing hepatic resection. Massive blood volume replacement may create physiologic derangements that have anesthetic and surgical consequences. These physiologic alterations include disorders of coagulation, acid-base imbalance, electrolyte imbalance, hypothermia, and decreased tissue oxygen delivery.
Many children undergoing tumor resection require postoperative ventilatory support. The anesthetic plan should permit early tracheal extubation in the operating room. However, in the event that intraoperative findings reveal unresectable tumor, postoperative care should include observation in the pediatric intensive care unit and attention to changes in intravascular volume and blood pressure. Continued bleeding may require transfusion of blood or fresh frozen plasma, or even return to the operating room for surgical control.
▪ HIRSCHSPRUNG'S DISEASE PROCEDURES
The basic pathology underlying congenital megacolon, or Hirschsprung's disease, is a gangliosis, or total absence of ganglion cells, in the intrinsic nerve supply of the bowel. The aganglionic area extends proximally from the anal sphincter and involves varying lengths of colon. The normal nerve supply, consisting of Auerbach's plexuses and Meissner's plexuses, which together form the myenteric nerve complex of the bowel, usually becomes an increasingly diffuse network in the descending and terminal portions of the bowel. Absence of the ganglion cells, which occurs in approximately 1:10,000 infants, causes a condition resembling spasm in the area without ganglion cells, whereas the normal bowel proximal to the spastic portion undergoes tremendous distention, with retention of feces and intestinal obstruction or, in less serious cases, prolonged bouts of constipation. Although the cause of Hirschsprung's disease is unknown, defects in nonadrenergic, noncholinergic innervations may prevent relaxation of the aganglionic segment. Bealer and others (1994) have demonstrated that nitric oxide synthetase is deficient in the aganglionic colon of patients with Hirschsprung's disease and that this deficiency may prevent smooth muscle relaxation of the aganglionic segment. On a molecular level, mutations in the RET proto-oncogene have been found ( Sancandi et al., 2000 ).
In 10% to 20% of patients with Hirschsprung's disease, it is clinically present at birth. Symptomatic infants have delayed passage of meconium, irritability, failure to thrive, and abdominal distention. Older children may present with constipation, fecal soiling, and diarrhea. The major complication from Hirschsprung's disease is acute enterocolitis, a potentially life-threatening event. Diagnosis of Hirschsprung's disease is made by radiographic examination and confirmed by suction biopsy specimens from the rectum. Surgery is usually a two-stage procedure, with the initial procedure being a colostomy. The definitive surgical procedure is generally performed when the child is older (>1 year of age). The surgical approaches are varied and over time have undergone modifications ( Fig. 19-7 ). Attention has focused on the use of a one stage transoral endorectal pull-through approach ( Elhalaby et al., 2004 ). Each surgical technique has its own associated intraoperative and perioperative complications, but enterocolitis, wound dehiscence, anastomotic leakage, intestinal obstruction, and fecal soiling are common to all. All of these surgical procedures aim either to excise or to bypass the aganglionic portion of the bowel and to free and advance the remaining normal portion of bowel toward the rectum. These procedures are often long (6 to 8 hours) and involve surgical explorations through the perineum and abdomen.
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FIGURE 19-7 Graphic representation in lateral view of the three major operative procedures for Hirschsprung's disease. Evolution of each from left to right. Unshaded native rectum is aganglionic. Shaded, pulled-through bowel contains ganglion cells. A, State's procedure was a prototypic anterior resection of dilated rectosigmoid. Lengthy aganglionic segment remained. In Swenson's procedure an oblique anastomosis resulted in ganglion cells within 1 cm of the verge posteriorly. B, In the original Duhamel's operation, the oversewn native rectum enlarged as a blind loop, which resulted in a fecaloma that caused partial obstruction. In Martin's modification, the blind loop is obviated by complete division of the septum and anastomosis of the anterior walls of the native rectum and pulled-through colon. Bowel that contains ganglion cells reaches within 1 cm of the anal verge posteriorly. C, In the original Soave's procedure, full-thickness colon that contained ganglion cells was advanced through the demucosalized native rectal sleeve. Excess colon extended from the anus for several weeks before transection and delayed anastomosis. In the Boley modification, a primary anastomosis is done 1 cm above the verge. Ganglion cells are present circumferentially at that level. (From Philappart AI: Hirschsprung's disease. In Ashcraft KW, Holder TM:Pediatric surgery, 2nd ed. Philadelphia, 1993, WB Saunders.) |
Laparoscopic surgery has also been used in the treatment of Hirschsprung's disease ( Jona et al., 1998 ; Wulkan and Georgeson, 1998 ; Georgeson et al., 1999 ). The minimally invasive assisted pull-through technique is generally used for patients where the aganglianotic segment is confined to the rectum sigmoid or proximal left colon ( Georgeson, 2002 ). Anesthetic concerns for patients with Hirschsprung's disease are similar to those for any child having surgery. Maintaining body temperature and providing appropriate fluid therapy (for replacement of large third-space losses) are the major challenges for the anesthesiologist.
Anesthesia induction can be either by inhalation or intravenous means. Because of the surgical bowel manipulation and the relative obstructive nature of the underlying disease, nitrous oxide is discontinued after induction, and anesthesia is maintained with a mixture of air, oxygen, and potent inhalation agent. Long-term follow-up of patients with Hirschsprung's disease suggests that 25% of patients will require a reoperation and that between 19% and 25% of patients will develop enterocolitis ( Fortuna et al., 1996 ).
▪ SURGERY FOR APPENDICITIS
Acute appendicitis is a common condition in children. Although the mortality from acute appendicitis is rare (case-fatality ratio, 0.3%) ( Addiss et al., 1990 ), morbidity (peritonitis, abscess formation, wound infection) is related to the state of the appendix at the time of the operation. The highest incidence of appendicitis is found in patients aged 10 to 19 years. The incidence of perforation of the appendix in children appears to be about 30% to 45%, but in preschool children and infants it can be as high as 80%. The incidence of appendicitis appears to be affected by race and sex. The incidences of appendicitis is 1.4 to 1.6 times greater in whites than nonwhites, whereas the perforation rate for nonwhites is 22% compared with 18% for whites ( Addiss et al., 1990 ).
The signs and symptoms of appendicitis are variable. The incidence of negative appendectomy (surgery performed without positive appendicitis) is significant. In males, the negative appendectomy rate is about 9%, whereas in females, it is about 22%. In females, diagnostic accuracy decreases during childbearing years, whereas in males, diagnostic accuracy does not appear to be affected by age. Classically, the patient presents with periumbilical pain that eventually localizes to the right lower quadrant. Anorexia, nausea, and vomiting are frequent, as is a low-grade fever. Continued progression of the inflammatory course results in increased tenderness in the right lower quadrant as well as referred pain to the right lower quadrant on palpation of other areas of the abdomen. With advanced disease, gangrene and perforation of the appendix occur with ensuing peritonitis and possible abscess formation.
The pathophysiology of appendicitis is thought to be related to an obstruction of the lumen of the appendix with subsequent bacterial overgrowth and distention of the appendix. In untreated cases, distention and overgrowth lead to gangrene and rupture. Although there is some urgency in making the diagnosis and surgically removing the appendix, the operation is never so urgent that a proper review of the patient's medical history and physical assessment cannot be performed.
Preoperative anesthetic management of the child with diagnosed appendicitis includes concerns regarding fluid and electrolyte disorders. Because these children may have been vomiting and may be febrile, signs and symptoms of dehydration should be assessed and any fluid or electrolyte deficits corrected.
Once the child has been adequately volume resuscitated and a normal airway is anticipated, an intravenous rapid sequence induction with cricoid pressure is performed. Anesthetic technique (inhalation agents versus opioid-based techniques) may depend on the surgical technique used to remove the appendix. Although frequently the appendix is removed by laparotomy, the role of laparoscopy (especially in females) in both diagnosis and management is increasing ( Gilchrist et al., 1992 ; Kuster and Gilrey, 1992 ; Olsen et al., 1993 ). In a study by McAnena and others (1992) , the median postoperative hospitalization stay was one half and the rate of wound infection one third in patients undergoing laparoscopic appendectomy compared with patients undergoing open appendectomy. In a study involving 30 pediatric hospitals, Pansky and others (2003) noted significant variability in practice and resource utilization among the institutions. In addition, the length of stay did not differ between those patients who underwent an open or a laparoscopic appendectomy.
Regardless of surgical technique, monitoring of the patient includes electrocardiogram, pulse oximeter, temperature probe, blood pressure cuff, pre-cordial stethoscope, and end-tidal gas measurements. Depending on the patient's body temperature, active cooling techniques (cooling blanket, rectal acetaminophen suppositories, cool intravenous fluids, and cool intra-abdominal irrigations) may be needed to help lower the patient's temperature. The addition of inhalational anesthetic gases may also augment cooling by promoting cutaneous vasodilation with subsequent increased heat loss.
▪ INTUSSUSCEPTION REPAIR
Intussusception is produced by the invagination or telescoping of one portion of the intestine into another ( Fig. 19-8 ). It tends to occur more frequently in males than females. Over 50% of cases occur in children under 1 year of age, and less than 10% of cases occur in children older than 5 years. Ninety percent of cases have idiopathic causes, which are frequently seen in children less than 1 year of age. Older children are more likely to have Meckel's diverticulum, intestinal polyp, lymphoma, adhesions, trauma hemolytic uremic syndrome, or ectopic pancreatic nodule as an etiology. Intussusception has also been reported postoperatively and after blunt abdominal trauma ( Linke et al., 1998 ; Komadina and Smrkolj, 1998 ). In addition, there has been a reported association of rotavirus vaccine and intussusception ( Zanardia et al., 2001) .
|
FIGURE 19-8 Intussusception. (From deLorimier AA, Harrison MR: Pediatric surgery. In Dunphy JE, Way LW: Current surgical diagnosis and treatment. Los Altos. CA, 1979, Lange Medical Publisher.) |
The clinical presentation of acute intussusception involves sudden paroxysms of abdominal pain, bloody stools and an abdominal mass, although in one series of patients, 18% of the children had painless intussusception ( Hutchison et al., 1980 ). In a review of 14 published reports, Losek (1993) noted that bloody stools were present in 42% of patients. Occult blood was noted in 43% and abdominal masses were present in 62% of patients. Intussusception can also present with neurologic findings (lethargy, apnea, seizures, hypotonia, opisthotonus) similar to a picture of septic encephalopathy ( Conway, 1993 ). Other symptoms and signs may include diarrhea, vomiting, fever, and dehydration. In other children, intussusception can present as a chronic entity that may mimic gastroenteritis ( Shekhawat et al., 1992 ), whereas in neonates, intussusception may mimic necrotizing enterocolitis ( Price et al., 1993 ).
About 90% of intussusceptions are ileocolic, with the remainder being ileoileal and colocolic. Treatment for intussusception involves the administration of appropriate fluids to combat dehydration and radiologic or surgical attempts to reduce the invaginated bowel. Hydrostatic enemas with barium or air have been reported to be successful in 80% of patients. However, enemas are contraindicated in patients with evidence of peritonitis, shock, and intestinal perforation. Surgical laparotomy with manual reduction and/or resection as well as laparoscopic approaches have been described for the surgical management in patients with unsuccessful radiologic reduction and in patients with signs of intestinal perforation, peritonitis, and shock.
Anesthetic considerations include restoring electrolyte and fluid deficits. Shock should be treated before commencing anesthesia. The intravascular deficits may be further exacerbated by the presence of barium in the gastrointestinal tract. The child with an intussusception should also be considered at risk for aspiration, and because of the intestinal obstruction, nitrous oxide should be avoided. Anesthesia should be induced with intravenous agents. If hemodynamic instability is a concern, ketamine or etomidate should be used as the hypnotic agent for induction.
Copyright © 2008 Elsevier Inc. All rights reserved. - www.mdconsult.com
Motoyama & Davis: Smith's Anesthesia for Infants and Children, 7th ed.
Copyright © 2005 Mosby, An Imprint of Elsevier
▪ GENERAL THORACIC SURGERY
Thoracic surgery in children is performed for a wide variety of congenital, neoplastic, infectious, and traumatic lesions; these lesions are listed in Box 19-4 . The patient may be a few hours old with a congenital cystadenamatous malformation (CCAM) and life-threatening respiratory distress or an adolescent with an asymptomatic mediastinal tumor. Regardless of age or disease, four principles are common to all patients undergoing general anesthesia for thoracic surgery, as follows:
|
1. |
Preoperative evaluation and preparation can minimize intraoperative problems and improve the safety of the anesthetic. |
|
|
2. |
The anesthesiologist must be aware of potential intraoperative problems. |
|
|
3. |
Modern monitoring techniques have increased the safety with regard to anesthetic management. |
|
|
4. |
Surgical approaches and techniques are constantly changing as efforts are made by surgeons to use minimally invasive procedures. |
BOX 19-4
|
Common Thoracic Surgical Procedures in Children |
||||||||||||||||||||||||||||||||||||||||||
|
A thorough preoperative evaluation is essential in caring for the pediatric patient scheduled for thoracic surgery. Appropriate imaging and laboratory studies should be performed preoperatively according to the lesion involved. Guidelines for fasting, choice of premedication, and preparation of the operating room are used as for other infants and children scheduled for major surgery. Following induction of anesthesia, placement of an intravenous catheter, and tracheal intubation, arterial catheterization should be performed for most patients undergoing thoracotomy as well as those with severe lung disease having thoracoscopic surgery. This facilitates monitoring of arterial blood pressure during manipulation of the lungs and mediastinum as well as arterial blood gas tensions during single lung ventilation (SLV). For thoracoscopic procedures of relatively short duration in patients without severe lung disease, the insertion of an arterial catheter is not required. Placement of a central venous catheter is generally not indicated if peripheral intravenous access is adequate for projected fluid and blood administration.
Inhaled anesthetic agents are commonly administered in 100% O2 during maintenance of anesthesia. Isoflurane may be preferred due to less attenuation of hypoxic pulmonary vasoconstriction (HPV) compared with other inhaled agents, although this has not been studied in children ( Benumof et al., 1987 ). Nitrous oxide is avoided. Use of intravenous opioids may facilitate a decrease in the concentration of inhaled anesthetics used and thereby limit impairment of hypoxic pulmonary vasoconstriction. Alternatively, total intravenous anesthesia may be used with a variety of agents. The combination of general anesthesia with regional anesthesia and postoperative analgesia is particularly desirable for thoracotomy but may also be beneficial for thoracoscopic procedures, especially when thoracostomy tube drainage, a source of significant postoperative pain, is used following surgery. A variety of regional anesthetic techniques have been described for intraoperative anesthesia and postoperative analgesia, including intercostal and paravertebral blocks, intrapleural infusions, and epidural anesthesia (see Chapter 14 , Regional Anesthesia).
In awake patients, except for young infants, ventilation is normally distributed preferentially to dependent regions of the lung, so that there is a gradient of increasing ventilation from the most nondependent to the most dependent lung segments. Because of gravitational effects, perfusion normally follows a similar distribution, with increased blood flow to dependent lung segments; therefore, ventilation and perfusion are normally well matched. However, controlled ventilation under general anesthesia with decreased functional residual capacity and absent diaphragmatic contractions result in a reverse distribution of ventilation (see Chapter 2 , Respiratory Physiology). During thoracic surgery, these and other factors act to increase ventilation/perfusion ( / ) mismatch. Compression of the dependent lung in the lateral decubitus position may cause atelectasis. Surgical retraction, SLV, or both result in collapse of the operative lung. Hypoxic pulmonary vasoconstriction (HPV), which acts to divert blood flow away from underventilated lung regions, thereby minimizing / mismatch, may be diminished by the use of inhaled anesthetic agents and other vasodilating drugs. These factors apply similarly to infants, children, and adults. The overall effect of the lateral decubitus position on / mismatch, however, is different in infants than in older children and adults.
In adults with unilateral lung disease, oxygenation is optimal when the patient is placed in the lateral decubitus position with the healthy lung dependent (“down”) and the diseased lung nondependent (“up”) ( Remolina et al., 1981 ). Presumably, this is related to an increase in blood flow to the dependent, healthy lung and a decrease in blood flow to the nondependent, diseased lung due to the hydrostatic pressure (i.e., gravitational) gradient between the two lungs. This phenomenon promotes / matching in the adult patient undergoing thoracic surgery in the lateral decubitus position.
In infants with unilateral lung disease, however, oxygenation is improved with the healthy lung “up” ( Heaf et al., 1983 ). Several factors account for this discrepancy between adults and infants. Infants have a soft, easily compressible rib cage that cannot fully support the underlying lung. Functional residual capacity is closer to residual volume, making airway closure likely to occur in the dependent lung even during tidal breathing ( Mansell et al., 1972 ).
Finally, the infant's increased oxygen requirement, coupled with a small functional residual capacity, predisposes to hypoxemia. Infants normally consume 6 to 8 mL of O2/kg per min compared with a normal O2 consumption in adults of 2 to 3 mL/kg per min ( Dawes, 1973 ). For these reasons, infants are at an increased risk of significant oxygen desaturation during surgery in the lateral decubitus position.
▪ THORACOSCOPY
During the past decade, the use of video-assisted thoracoscopic surgery has dramatically increased in both adults and children (see discussion under “Video Endoscopy”). As with laparoscopy, reported advantages of thoracoscopy include smaller chest incisions, reduced postoperative pain, and more rapid postoperative recovery compared with thoracotomy ( Weatherford et al., 1995 ; Angellilo et al., 1996; Mouroux et al., 1997 ).
Thoracoscopic surgery is being used extensively for pleural debridement in patients with empyema, lung biopsy and wedge resections for interstitial lung disease, mediastinal masses, and metastatic lesions. More extensive pulmonary resections, including segmentectomy and lobectomy, have been performed for lung abscess, bullous disease, sequestrations, lobar emphysema, CCAM, and neoplasms. Other thoracoscopic procedures are listed in Table 19-4 .
TABLE 19-4 -- Thoracoscopic procedures in infants and children
|
Thoracoscopy can be performed while both lungs are being ventilated using CO2 insufflation and placement of a retractor to displace lung tissue in the operative field. However, SLV is extremely desirable during thoracoscopy because lung deflation improves visualization of thoracic contents and may reduce lung injury caused by the use of retractors ( Benumof, 1995 ).
▪ SURGERY FOR CHEST WALL DEFORMITIES
Pectus excavatum (funnel chest) ( Fig. 19-9 ) and the less common pectus carinatum (pigeon breast) deformities are congenital abnormalities of the sternum, ribs, and costal cartilages. These deformities are usually minimal at birth but progress with age. A higher incidence of both deformities occurs in children with Marfan's syndrome or congenital heart disease and in families in which other children have the defect (Rubicsek, 2000).
|
FIGURE 19-9 Pectus excavatum deformity becomes most obvious when the child is in the sitting position. |
These children often appear asymptomatic but occasionally have cardiac or pulmonary abnormalities related to the deformity. Patients with pectus excavatum generally present with normal or modestly reduced forced vital capacity and total lung capacity and, in severe cases, / mismatch. The heart is displaced to the left and compressed, lending to arrhythmias, right-axis deviation on electrocardiogram, a functional murmur, and reduced stroke volume most noticeable in the standing position and during exercise, explaining the mild exercise intolerance experienced by some patients. The cardiac and pulmonary abnormalities are in most instances benign and may worsen as the child ages but may be improved by surgical repair. There also is an increased incidence of mitral valve prolapse in patients with pectus deformities.
Preoperative assessment focuses on exercise tolerance and other signs of cardiopulmonary compromise, such as lung infections. Laboratory evaluation includes a chest radiograph with pulmonary function tests, arterial blood gases, or electrocardiogram added only if there is clinical evidence of significant underlying disease. Echocardiography is now commonly performed to detect the presence of mitral valve prolapse. If the child has mitral valve prolapse, prophylaxis for subacute bacterial endocarditis is administered. Patients are often emotionally distressed by the appearance of chest deformity and may benefit from preoperative counseling and, if needed, premedication.
Classic operative repair involves extrapleural excision of the sternocostal cartilages and mobilization of the sternum and ribs. The most common complications of operative repair are pneumothorax, flail chest, and postoperative atelectasis; blood loss is usually minimal to moderate. Intraoperative monitors include temperature, blood pressure, pulse, heart and breath sounds, airway pressure, and oxygen saturation or tension. Capnography is also useful, while arterial catheterization is needed only if there is a specific indication. General anesthesia with controlled ventilation is the method of choice, with no agents specifically indicated or contraindicated because of the operation itself. Oxygen by facemask is administered in the recovery room, but it is usually not needed after the child fully awakens. Although patient-controlled analgesia is commonly used for postoperative analgesia, both intercostal nerve blocks and thoracic epidural analgesia have become increasingly popular for children undergoing pectus repair ( Robicsek, 2000 ).
A thoracic epidural catheter provides more reliable analgesia to the operative area than a lumbar epidural that has been threaded up a great distance. However, thoracic epidural catheters are not as easy to insert as lumbar catheters, and many practitioners are not comfortable with their routine use. Although a technique using electrocardiographic guidance and insertion from the caudal space has been described, it is not widely used ( Tsui, 2002) . An additional issue with the thoracic catheters is the safety of their insertion under general anesthesia ( Horlocker, 2003) . Although some children allow insertion before induction ( McBride, 1996) , many younger children are not likely to remain cooperative for the procedure, mandating insertion after induction ( Hammer, 2002 ; Birmingham, 2003) . Moreover, several centers have actively and successfully used thoracic epidural techniques in anesthetized children for thoracic and cardiac procedures without complications related to insertion after induction ( Cassady, 2000 ; Birmingham, 2003) . Solutions of both bupivacaine with fentanyl and fentanyl alone have been used successfully, including in the patient-controlled mode for appropriately mature children ( Birmingham, 2003 ; Caudle, 1993) (see Chapter 14 , Pediatric Regional Anesthesia).
Another approach has used a minimally invasive technique in which the costal cartilages are preserved and the sternum is elevated with a bar. Under direct vision and through a thorascope, a transmediastinal tunnel is created and a prebent bar is passed behind the sternum with the convex side down. The bar is then rotated 180 degrees in order to elevate the sternum ( Nuss et al., 1998 ; Nuss, 2002) . Borowitz and others (2003) have shown that static pulmonary function and ventilatory response to exercise was normal both before and after surgery, thereby suggesting that placement of the bar does not result in an increased chest wall restriction. In addition, Lawson and others (2003) noted that the surgical repair of the pectus excavatum following the Nuss procedure had a positive impact on both the patient's physical and emotional well-being. Complications of this minimally invasive approach include atelectasis, subcutaneous emphysema, pericardial and pleural effusions, myocardial perforation, diaphragmatic perforation, and dislocation of the stabilizing bar ( Willekes, 1999 ; Molik, 2001 ; Moss, 2001 ; Hosie et al., 2002 ; Uemura et al., 2003 ). Postoperative pain following the Nuss procedure is significant. Thoracic epidural analgesia for 2 to 3 days followed by oral opioid therapy is appropriate.
▪ THORACOTOMY, LOBECTOMY, AND PNEUMONECTOMY
Thoracotomy in the infant or child can be indicated for congenital abnormalities (cysts), tumors (mediastinal teratomas), trauma (gunshot wounds), or infective lesions (bronchiectasis). Subsegmental resection is used for biopsy and removal of metastatic tumors, whereas lobectomy is most commonly used for removal of congenital anomalies and extensive tumor metastasis. Pneumonectomy in children is done for various tumors, congenital abnormalities, and inflammatory lesions, such as bronchiectasis. Perioperative management differs dramatically, depending on the indication for surgery.
Surgical Lesion
If a space-occupying lesion is present, the patient is examined for signs of decreased cardiac output, diminished lung volume and reserve, and airway compression ( Keon, 1981 ). History focuses not only on general exercise tolerance but also on signs of intermittent airway obstruction (stridor, cyanosis, or wheezing). Physical examination includes checking for a shift in the trachea, asymmetric chest movement, wheezing, and any signs of respiratory distress. Laboratory assessment should include a chest radiograph, but additional studies, such as tomograms, angiography, or computed tomography (CT), often provide more exact data about vascular or airway compression and compromise. It is crucial to determine the extent of airway compression and physiologic compromise because impairment may worsen with induction of anesthesia as sympathetic and muscular tones are reduced.
If the intrathoracic lesion is a primary or metastatic tumor, the history concentrates on previous treatment ( Baldeyrou et al., 1984 ). Previous treatment for the tumor, especially chemotherapy and radiation, is important. Special attention is given to anthracycline (cardiac toxicity), bleomycin (pulmonary toxicity), and steroid (adrenal suppression) therapy. If there is any question about functional disability caused by this treatment, consultation with the child's oncologist is useful. Anemia, thrombocytopenia, and malnutrition are common in these patients and should be improved before surgery ( Beattie, 1984). A special consideration is the immunocompromised patient with an unknown pulmonary infiltrate. This is usually assumed to be an opportunistic infection, but because it may represent metastasis, a biopsy is occasionally requested. These patients are often in poor general condition, and they may require postoperative ventilatory support, especially if they had only marginal compensation before surgery ( Imoke et al., 1983 ; Prober et al., 1984 ).
Assessment
General assessment of the child starts with vital signs and overall appearance. Because children tolerate the loss of large amounts of usable lung tissue without obvious distress, the appearance of dyspnea or diminished exercise tolerance is an ominous sign. The history in older children focuses on complaints of dyspnea, cyanosis, wheezing, coughing, and weight loss. Infants often show less specific signs, such as poor feeding, irritability, choking, or change in sleep habits. If the child has had previous surgery, the perioperative course should be examined. The chest is inspected for asymmetric expansion and use of accessory muscles and then is auscultated for wheezes, rales, rhonchi, and absent breath sounds in both the supine and sitting positions. Physical assessment of the cardiovascular system concentrates on the presence of a gallop, murmurs, arrhythmias, and adequate peripheral pulses.
Preparation
Preparation for surgery starts with a discussion of the proposed anesthetic with the parents and, if appropriate, the child. The anesthetic plan, including monitors, possible complications, and potential for postoperative ventilation, is discussed. It is best to delay surgery until any infection or bronchospasm has been brought under optimal medical control with antibiotics, chest physiotherapy, and bronchodilators, as needed ( Sutton et al., 1983 ). It may be difficult or impossible to eradicate infections or bronchospasm completely in destructive lesions such as bronchiectasis. If this is the case, it is acceptable to proceed after reasonable medical therapy has optimized the patient's status so that no further improvement is anticipated.
Monitoring
At a minimum, thoracotomy requires monitoring of inspired oxygen, blood pressure, heart and breath sounds, airway pressure, and temperature, as well as an electrocardiogram. Oxygen saturation by pulse oximeter or, less commonly, by transcutaneous oxygen tension (Po2) monitor ( Harnick et al., 1983 ) is vital for detection of sudden changes in oxygenation from lung compression or kinking of the airway. Capnography is particularly useful for detecting sudden changes in effective ventilation. Arterial cannulation for pressure and arterial blood samples is useful and is needed if extensive blood loss or resection of lung tissue is expected or if the child is already critically ill. Percutaneous arterial cannulas (24 gauge in neonates, 22 gauge in children up to 8 to 10 years of age, and 20 gauge in preadolescents and older) can be inserted in children and should be used whenever indicated. Central venous monitoring is used less commonly but can be helpful for guiding extensive volume replacement. Urinary drainage is a consideration for particularly long procedures.
Positioning
Positioning of the patient has often been used to minimize spillage of lung contents because double-lumen tubes are impractical in smaller patients ( Conlan et al., 1986 ). Suction through the ETT may not be adequate to control large quantities of pus freed during surgical manipulation. The prone and lateral positions are the most commonly used. Positioning can cause significant ventilatory changes in children. Functional residual capacity (FRC) decreases during general anesthesia ( Motoyama et al., 1982 ) but actually increases when the child is turned to the lateral position. The increase in FRC and ventilation occurs mainly in the uppermost part of the lung. The FRC falls dramatically once the pleura is opened ( Larsson et al., 1987 ). The practical problems of dislodgment of the ETT with movement and adequate padding in these positions are especially important in children. Open-celled foam with adhesive backing (Reston; 3M, St. Paul, MN) can be applied to the thorax, pelvic rim, and other pressure points to minimize the effects of positioning. Also, the tube position must be rechecked each time the patient is moved.
Anesthesia
General endotracheal anesthesia presents various challenges to the anesthesiologist. A quiet, smooth inhalation induction is often used in infants and smaller children, whereas an intravenous induction is used in the older child. If there is concern about spillage of lung contents, rapid securing of the airway with intravenous induction is preferred to minimize coughing. The choice of appropriate anesthetic agents depends on both the patient's status and the surgical lesion. Nitrous oxide can accumulate in cysts with air-fluid levels and should be avoided in these patients or in patients requiring a high fraction of inspired oxygen (FIO2). Volatile agents are especially useful in patients with bronchospastic disorders. The rate of rise of inhalational anesthetics may be slowed in the presence of intrapulmonary shunting. Precipitous hypotension is another potential problem with volatile agents in patients with low cardiac reserve. Muscle relaxants are routinely used along with controlled ventilation employing humidified gases. Although mechanical ventilators are usually acceptable, manual ventilation provides useful information to the anesthesiologist about changes in compliance or airway resistance, especially in infants or in procedures where there is recurrent obstruction of the airway.
Single-Lung Ventilation Techniques
Single-Lung Ventilation Using a Single-Lumen Endotracheal Tube.
The simplest means of providing SLV is to intentionally intubate the ipsilateral mainstem bronchus with a conventional single-lumen ETT ( Rowe et al., 1994 ). When the left bronchus is to be intubated, the bevel of the ETT is rotated 180 degrees and the head is turned to the right ( Kubota et al., 1987 ). The ETT is advanced into the bronchus until breath sounds on the operative side disappear. A fiberoptic bronchoscope may be passed through or alongside the ETT to confirm or guide placement. When a cuffed ETT is used, the distance from the tip of the tube to the distal cuff must be shorter than the length of the bronchus so that the ETT does not occlude the upper lobe bronchus ( Lammers et al., 1997 ) ( Fig. 19-10 ). This technique is simple and requires no special equipment other than a fiberoptic bronchoscope. This may be the preferred technique of SLV in emergency situations such as airway hemorrhage or contralateral tension pneumothorax.
|
FIGURE 19-10 Obstruction of the left upper lobe bronchus with a cuffed endotracheal tube used for left-sided single-lung ventilation. |
Problems can occur when using a single-lumen ETT for SL If a smaller, uncuffed ETT is used, it may be difficult to provide an adequate seal of the intended bronchus. This may prevent the operative lung from adequately collapsing or fail to protect the healthy, ventilated lung from contamination by purulent material from the contralateral lung. The operative lung cannot be suctioned using this technique. Hypoxemia may occur due to obstruction of the upper lobe bronchus, especially when the short right mainstem bronchus is intubated.
Single-Lung Ventilation Using a Balloon-Tipped Bronchial Blocker.
A Fogarty embolectomy catheter or an end-hole, balloon wedge catheter may be used for bronchial blockade to provide SLV ( Fig. 19-11 ) ( Ginsberg, 1981 ; Lin and Hackel, 1994 ; Hammer et al., 1996 ;Turner et al., 1997 ). Placement of a Fogarty catheter is facilitated by bending the tip of its stylette toward the bronchus on the operative side. A fiberoptic bronchoscope is used to reposition the catheter and confirm appropriate placement. When an end-hole catheter is placed outside the ETT, the bronchus on the operative side is initially intubated with an ETT. A guidewire is then advanced into that bronchus through the ETT. The ETT is removed and the blocker is advanced over the guidewire into the bronchus. An ETT is then reinserted into the trachea alongside the blocker catheter. The catheter balloon is positioned in the proximal mainstem bronchus under fiberoptic visual guidance. With an inflated blocker balloon, the airway is completely sealed, providing more predictable lung collapse and better operating conditions than with an ETT in the contralateral bronchus.
|
FIGURE 19-11 Balloon-tipped catheters used as bronchial blockers for single-lung ventilation. A, Fogarty catheter. B, Arrow balloon wedge catheter. C, Cook endobronchial blocker. |
A potential problem with this technique is dislodgment of the blocker balloon into the trachea. The inflated balloon then blocks ventilation to both lungs, prevents collapse of the operated lung, or both. The balloons of most catheters currently used for bronchial blockade have low-volume, high-pressure properties and overdistention can damage or even rupture the airway ( Borchardt et al., 1998 ). A study, however, reported that bronchial blocker cuffs produced lower “cuff to tracheal” pressures than double-lumen tubes ( Guyton et al., 1997 ). When closed tip bronchial blockers are used, the operative lung cannot be suctioned and continuous positive airway pressure (CPAP) cannot be provided to the operative lung if needed.
When a bronchial blocker is placed outside the ETT, care must be taken to avoid injury caused by compression and resultant ischemia of the tracheal mucosa. The sum of the catheter diameter and the outer diameter of the ETT should not exceed the tracheal diameter. Outer diameters for pediatric ETTs are shown in Table 19-5 .
TABLE 19-5 -- Diameters of pediatric endotracheal tubes
|
ID (mm) |
OD (mm)[*] |
|
3.0 |
4.3 |
|
3.5 |
4.9 |
|
4.0 |
5.5 |
|
4.5 |
6.2 |
|
5.0 |
6.8 |
|
5.5 |
7.5 |
|
6.0 |
8.2 |
|
6.5 |
8.9 |
|
7.0 |
9.6 |
|
ID, internal diameter. Cuffed tubes have approximately 0.5-mm additional outer diameter (OD). |
|
* |
Sheridan Tracheal Tubes, Kendall Healthcare, Mansfield, MA. |
Adapters have been used that facilitate ventilation during placement of a bronchial blocker through an indwelling ETT ( Takahashi et al., 2000 ; Arndt et al., 1999 ). Use of a 5F endobronchial blocker that is designed for use in children with a multiport adapter and fiberoptic bronchoscope (FOB) has been described (Cook Critical Care, Inc., Bloomington, IN) (Hammer et al., 2001). The balloon is elliptical in shape so that it conforms to the bronchial lumen when inflated. The blocker catheter has a maximum outer diameter of 2.5 mm (including the deflated balloon), a central lumen with a diameter of 0.7 mm, and a distal balloon with a capacity of 3 mL. The balloon has a length of 1.0 cm, corresponding to the length of the right mainstem bronchus in children approximately 2 years of age ( Scammon, 1923 ). The blocker is placed coaxially through a dedicated port in the adapter, which also has a port for passage of an FOB and ports for connection to the anesthesia breathing circuit and ETT ( Fig. 19-12 ). The FOB port has a plastic sealing cap, whereas the blocker port has a Tuohy-Borst connector, which locks the catheter in place and maintains an air-tight seal. Because oxygen can be administered during passage of the blocker and FOB, the risk of hypoxemia during blocker placement is diminished, and repositioning of the blocker may be performed with fiberoptic guidance during surgery.
|
FIGURE 19-12 The Cook 5F endobronchial catheter is shown inserted in the multiport adapter (Cook Critical Care, Inc., Bloomington, IN). The adapter has four ports for connection to (A, clockwise from bottom) the breathing circuit, fiberoptic bronchoscope (FOB), endobronchial catheter, and endotracheal tube. After the FOB and endobronchial catheter have been inserted through the multiport adaptor, the FOB is placed through the monofilament loop at the distal end of the catheter (arrow). The multiport adaptor is then attached to the indwelling endotracheal tube (B) and the breathing circuit (C). The FOB is directed into the mainstem bronchus on the operative side. The catheter is then advanced until the monofilament loop slides off the end of the FOB into the bronchus. |
When the placement of a bronchial blocker inside the ETT is guided by an FOB, both the blocker catheter and FOB must pass through the indwelling ETT. The inner diameter of the ETT through which the catheter and FOB are to be placed must be larger than the sum of the outer diameters of the catheter and the FOB. The 5F blocker catheter and an FOB with a 2.2-mm diameter, for example, may be inserted through an ETT as small as 5.0-mm internal diameter (ID). For children with an indwelling ETT smaller than 5.0 mm ID, a blocker catheter can be positioned under fluoroscopy ( Fig. 19-13 ).
|
FIGURE 19-13 Positioning of a bronchial blocker under fluoroscopy. A, The catheter has been advanced into a segmental bronchus on the left. B, The catheter has been pulled back so that the balloon is in the left mainstem bronchus. |
Single-Lung Ventilation Using a Univent Tube.
The Univent tube (Fuji Systems Corporation, Tokyo, Japan) is a single-lumen ETT with a second lumen containing a small blocker catheter that can be advanced into a bronchus ( Fig. 19-14 ) ( Kamaya and Krishna, 1985 ; Kawande, 1987; Gayes, 1993 ). A balloon located at the distal end of this small tube serves as a blocker. Univent tubes require a fiberoptic bronchoscope for successful placement. Univent tubes are now available in sizes as small as 3.5- and 4.5-mm ID for use in children over 6 years of age ( Table 19-6 ) ( Hammer et al., 1998 ). Because the blocker tube is firmly attached to the main ETT, displacement of the Univent blocker balloon is less likely than when other blocker techniques are used. The blocker of the 4.5 Univent tube has a small lumen, which allows egress of gas and can be used to insufflate oxygen or suction the operated lung.
|
FIGURE 19-14 The Univent tube is a single-lumen endotracheal tube with a second lumen containing a small blocker catheter. |
TABLE 19-6 -- Univent tube diameters
|
ID (mm) |
OD (mm)[*] |
|
3.5 |
7.5/8.0 |
|
4.5 |
8.5/9.0 |
|
6.0 |
10.0/11.0 |
|
6.5 |
10.5/11.5 |
|
7.0 |
11.0/12.0 |
|
7.5 |
11.5/12.5 |
|
8.0 |
12.0/13.0 |
|
8.5 |
12.5/13.5 |
|
9.0 |
13.0/14.0 |
|
ID, internal diameter; OD, outer diameter. |
|
* |
Sagittal/transverse. |
A disadvantage of the Univent tube is the large amount of cross sectional area occupied by the blocker channel, especially in the smaller-size tubes. Smaller Univent tubes have a disproportionately high resistance to gas flow ( Slinger and Lesiuk, 1998 ). The Univent tube's blocker balloon has low-volume, high-pressure characteristics so mucosal injury can occur during normal inflation ( Benumof et al., 1992 ; Kelley et al., 1992 ).
Single-Lung Ventilation Using a Double-Lumen Tube.
All double-lumen tubes (DLTs) are essentially two tracheal tubes of unequal length molded longitudinally together. The shorter tube ends in the trachea, and the longer tube, in the bronchus. Marrarro (1994)described a bilumen tube for infants. DLTs for older children and adults have cuffs located on the tracheal and bronchial lumens. The tracheal cuff, when inflated, allows positive pressure ventilation. The inflated bronchial cuff allows ventilation to be diverted to either or both lungs and protects each lung from contamination from the contralateral side.
Conventional plastic DLTs, once only available in adult sizes (35F, 37F, 39F, and 41F), are now available in smaller sizes ( Table 19-7 ). The smallest cuffed DLT is 26F (Rusch, Duluth, GA), which may be used in children as young as 8 years of age. DLTs are also available in sizes 28F and 32F (Mallinckrodt Medical, Inc., St. Louis, MO) suitable for children 10 years of age and older.
TABLE 19-7 -- Tube selection for single-lung ventilation in children
|
Age (yr) |
ETT (ID)[*] |
BB (F) |
Univent[†] |
DLT (F) |
|
0.5 to 1 |
3.5 to 4.0 |
2[‡] |
||
|
1 to 2 |
4.0 to 4.5 |
3[‡] |
||
|
2 to 4 |
4.5 to 5.0 |
5[§] |
||
|
4 to 6 |
5.0 to 5.5 |
5[§] |
||
|
6 to 8 |
5.5 to 6 |
5[§] |
3.5 |
|
|
8 to 10 |
6.0 Cuffed |
5[§] |
3.5 |
26[‖] |
|
10 to 12 |
6.5 Cuffed |
5[§] |
4.5 |
26[‖] to 28[¶] |
|
12 to 14 |
6.5 to 7.0 Cuffed |
5[§] |
4.5 |
32[¶] |
|
14 to 16 |
7.0 Cuffed |
5[§] |
6.0 |
35[¶] |
|
16 to 18 |
7.0 to 8.0 Cuffed |
9[§] |
7.0 |
35[¶] |
|
BB, bronchial blocker; ETT, endotracheal tube; ID, internal diameter; DLT, double-lumen tube; F, French. |
|
* |
Sheridan Tracheal Tubes, Kendall Healthcare, Mansfield, MA. |
|
† |
Edwards Lifesciences LLC, Irvine, CA. |
|
§ |
Cook Critical Care, Inc., Bloomington, IN. |
|
‡ |
Fuji Systems Corporation, Tokyo, Japan. |
|
‖ |
Rusch, Duluth, GA. |
|
¶ |
Mallinckrodt Medical, Inc., St. Louis, MO. |
DLTs are inserted in children using the same technique as in adults ( Brodsky and Mark, 1983 ). The tip of the tube is inserted just past the vocal cords and the stylette is withdrawn. The DLT is rotated 90 degrees to the appropriate side and then advanced into the bronchus. In the adult population, the depth of insertion is directly related to the height of the patient ( Brodsky et al., 1996 ). No equivalent measurements are yet available in children. If fiberoptic bronchoscopy is to be used to confirm tube placement, an FOB with a small diameter and sufficient length must be available ( Slinger, 1989 ).
A DLT offers the advantage of ease of insertion as well as the ability to suction and oxygenate the operative lung with CPAP. Left DLTs are preferred to right DLTs because of the shorter length of the right main bronchus ( Benumof et al., 1987 ). Right DLTs are more difficult to accurately position because of the greater risk of right upper lobe obstruction. DLTs are safe and easy to use. There are very few reports of airway damage from DLTs in adults, and none in children. Their high-volume, low-pressure cuffs should not damage the airway if they are not overinflated with air or distended with nitrous oxide while in place. Guidelines for selecting appropriate tubes (or catheters) for SLV in children are shown in Table 19-7 . There is significant variability in overall size and airway dimensions in children, particularly in teenagers. These recommendations are based on average values for airway dimensions. Larger DLTs may be safely used in adult-size teenagers.
Postoperative Care
Tracheal extubation at the completion of surgery is often possible after simple subsegmental resection or lobectomy. However, the patient's underlying cardiopulmonary reserve, the course of the surgery, and the expected postoperative course may preclude extubation. Although postoperative pain can cause significant splinting, intercostal or epidural blocks, coupled with judicious parenteral opioids, can minimize the discomfort (see Chapters 13 and 14 , Pain Management and Regional Anesthesia). Whether in the operating room or in the intensive care area, before extubation the patient must be awake, breathing well, able to cough and maintain an airway, and able to maintain acceptable oxygenation with no more than 40% inspired oxygen. A chest radiograph should be obtained as soon as possible after surgery to detect any significant pneumothorax or atelectasis. Atelectasis is common and usually responds to humidity, encouragement to cough, CPAP, and, if necessary, endotracheal suction.
The expected postoperative course depends on both the surgical procedure and the underlying diseases. After simple lobectomy, most children develop normally and have normal exercise tolerance (McBride et al., 1980 ). Children who have undergone pneumonectomy may have more problems ( Buhain and Brody, 1973 ). With time, overinflation of the remaining lung occurs, with a demonstrable decrease in vital capacity. These children may have significant exercise intolerance for a prolonged period after surgery.
▪ SURGERY IN CONGENITAL LOBAR EMPHYSEMA, PULMONARY SEQUESTRATION, AND CYSTIC LESIONS
CONGENITAL LOBAR EMPHYSEMA
Congenital lobar emphysema is a rare cause of sudden respiratory distress in infants ( Leape and Longino, 1964 ). Hyperinflation and progressive air trapping cause expansion of the affected lobe, along with compression of other lung tissue, mediastinal shifting, and impaired venous return. The most commonly affected is the left upper lobe, followed by the right middle and upper lobes. Occasionally more than one lobe is affected. The cause of the obstruction is unknown in most cases, although many show evidence of deficient and disordered bronchial cartilage. In some cases there are identifiable causes of bronchial compression, such as aberrant blood vessels, bronchial cysts, and bronchial stenosis. Finally, some patients have widespread lung disease with poor elastic recoil throughout ( Ryckman and Rosenkrantz, 1985 ).
Congenital lobar emphysema usually appears clinically between the newborn period and the first 6 months of life ( Murray, 1967 ) with tachycardia and retractions. The child may have rapid, progressive accumulation of gas in the affected lobe. Physical examination reveals asymmetric expansion of the thorax, wheezing, displacement of the cardiac impulse, hyperresonance to percussion, and diminished breath and heart sounds. Chest radiographs ( Fig. 19-15 ) show overdistention of the affected lobe, mediastinal shift, and atelectasis in other lobes. The chest radiograph can help differentiate lobar emphysema from pneumothorax or congenital cysts by the presence of faint bronchovascular markings and herniation of the affected lobe across the midline.
|
FIGURE 19-15 Right-sided congenital lobar emphysema. A, The right lung appears hyperinflated and lucent and may be mistaken for a pneumothorax. B, Computed tomography scan reveals markedly hyperexpanded right lung, mediastinal shift to the left, and compression of the left lung. |
Infants who show rapid deterioration constitute a surgical emergency to relieve the expanding lobe with its ventilatory and cardiac impairment. Many patients do not have a clear clinical picture, however, but rather have a vague history of intermittent cyanosis or respiratory distress, failure to thrive, or unusual respiratory distress with feeding or a cold. Lobar emphysema is also seen in preterm infants with respiratory distress who are undergoing mechanical ventilation, which most frequently develops in the right upper lobe.
Preoperative evaluation depends on the degree of patient distress ( Payne et al., 1984 ). If there is rapid deterioration, evaluation is limited. Chest tube placement, needle aspiration of the trapped air, and vigorous mechanical ventilation have been tried as palliative procedures but are associated with a much higher mortality than thoracotomy and lobectomy. If the patient is stable and there is any question about the diagnosis, procedures such as radioisotope perfusion scans, angiography, or CT imaging can be used before proceeding with definitive surgery. During preanesthetic evaluation, cardiopulmonary stability of the patient is the prime concern. The degree of distress, its progression, and the need for supplemental oxygen are key components of the examination. Cardiac evaluation is important because these patients have a higher incidence of congenital heart disease, especially ventricular septal defect.
Monitoring includes pulse oximetry to detect rapid changes in oxygenation, especially with induction. In deteriorating patients, there may be little time to establish intra-arterial monitoring before incision. Doppler-assisted or automated blood pressure cuffs increase the accuracy of measurements and are especially useful in infants. After intubation, capnography is helpful.
Induction of anesthesia in infants with congenital lobar emphysema is a critical phase in the anesthetic management. The crying, struggling infant can increase the amount of trapped gas, whereas positive-pressure ventilation or positive airway pressure by the anesthesiologist can also increase the emphysema. A smooth inhalation induction with sevoflurane and oxygen is often used, with positive-pressure ventilation minimized until the chest is open (Coté, 1978). Controlled or assisted ventilation is added if unacceptable hypoventilation develops, whereas intubation is performed with or without muscle relaxants, depending on the patient's tolerance of positive-pressure ventilation. High-frequency ventilation has been used successfully in infants with lobar emphysema ( Goto et al., 1987 ) and should be considered if the practitioner is familiar with the technique. The low airway pressures are especially suitable for these patients. Nitrous oxide is avoided because it can expand the emphysematous areas (Payne et al., 1984 ). If the lobe expands suddenly, the surgeon should be ready to open the chest immediately and relieve the pressure. Raghavendran and others (2001) have also described a technique involving caudal epidural catheter threaded to the thoracic level in spontaneously breathing patients who were anesthetized with potent inhaled anesthetic agents.
An alternative induction approach, especially for unstable infants, is sedation with intravenous ketamine (1 to 2 mg/kg) and local anesthetic infiltration of the incision site (Coté, 1978). After the intrathoracic pressure has been relieved, general anesthesia can proceed with any technique appropriate to the patient's underlying status. Older children who are stable often undergo bronchoscopy before thoracotomy to rule out a foreign body or other correctable lesions. After induction with oxygen and a volatile agent, thorough topical anesthesia with 2% to 4% lidocaine (not more than 4 to 6 mg/kg) smoothes the course. As with the younger patient, rapid surgical decompression may be needed as the case proceeds.
In most patients, the trachea can be extubated at the end of the lobectomy. Humidity, coughing, and early increases in activity or ambulation minimize atelectasis in the immediate postoperative period. These children do well clinically after surgery but have reduced forced vital capacity and delayed forced expiration, not only in the immediate postoperative period but throughout childhood ( Eigen et al., 1976 ; McBride et al., 1980 ).
Pulmonary Sequestrations
Pulmonary sequestrations result from disordered embryogenesis producing a nonfunctional mass of lung tissue supplied by anomalous systemic arteries. Presenting signs include cough, pneumonia, and failure to thrive and often present during the neonatal period, usually before the age of 2 years. Diagnostic studies include CT scans of the chest and abdomen and arteriography. Magnetic resonance imaging (MRI) may provide high-resolution images, including definition of vascular supply. This may obviate the need for angiography. Surgical resection is performed following diagnosis. Pulmonary sequestrations do not generally become hyperinflated during positive pressure ventilation. Nitrous oxide administration may result in expansion of these masses, however, and should be avoided.
Congenital Cystic Lesions
Congenital cystic lesions in the thorax may be classified into three categories ( Kravitz, 1994 ). Bronchogenic cysts result from abnormal budding or branching of the tracheobronchial tree. They may cause respiratory distress, recurrent pneumonia, and/or atelectasis due to lung compression. Dermoid cysts are clinically similar to bronchogenic cysts but differ histologically, as they are lined with keratinized, squamous epithelium rather than respiratory (ciliated columnar) epithelium. They usually present later in childhood or adulthood. Cystic adenomatoid malformations (CCAM) are structurally similar to bronchioles but lack associated alveoli, bronchial glands, and cartilage ( Ryckman and Rosenkrants, 1985) . Because these lesions communicate with the airways, they may become overdistended due to gas trapping, leading to respiratory distress in the first few days of life. When they are multiple and air filled, CCAM may resemble congenital diaphragmatic hernia (CDH) radiographically. Treatment is surgical resection of the affected lobe. As with CDH, prognosis depends on the amount of remaining lung tissue, which may be hypoplastic due to compression in utero ( Schwartz and Ramachandran, 1997).
▪ SURGERY FOR DISEASES OF THE MEDIASTINUM
Surgical problems of the mediastinum fall into three major categories: masses, infections, and pneumomediastinum. The mediastinum is functionally divided into anterior, middle, and posterior segments. This classification is useful diagnostically in evaluating defects because of the propensity of lesions to develop primarily in only one of the divisions ( Table 19-8 ).
TABLE 19-8 -- Mediastinal masses
|
Location |
Presentation |
|
Anterior Division |
|
|
Lymphomas |
Superior vena cava syndrome |
|
Lymphangiomas (cystic hygroma) |
Cardiac tamponade |
|
Teratomas |
Tracheal and lung compression |
|
Thymomas and thymic cysts |
|
|
Middle Division |
|
|
Bronchogenic cysts |
Airway obstruction |
|
Granulomas |
Stridor |
|
Lymphomas |
Obstructive emphysema |
|
Posterior Division |
|
|
Enteric cysts, duplications |
Airway obstruction |
|
Neuroblastoma |
Recurrent pneumonias |
|
Ganglioneuroma, neurofibroma |
Dysphagia |
Masses in the anterior portion of the mediastinum tend to be lymphomas, lymphangiomas (cystic hygroma), and teratomas. Thymomas and thymic cysts can appear here but are rare in childhood. Lymphomas are primarily of the Hodgkin's type, and biopsy of them is done only for diagnostic purposes. The survival of the child with mediastinal lymphoma depends on the systemic spread of the tumor and not on the amount of lymphoma present in the mediastinum. Lymphangiomas are often extensions of cystic hygromas from the cervical region into the mediastinum. If not all of the lymphangioma is removed at initial resection, further extension may occur. Anterior mediastinal masses can present in various ways. Although they may be asymptomatic and detected incidentally on a chest radiograph, they may also present as compression of pulmonary or vascular structures. Superior vena cava syndrome, cardiac tamponade, and both tracheal and lung compression can be prominent characteristics ( Levin et al., 1985 ; Northrip et al., 1986 ).
Bronchogenic cysts, granulomas, and lymphomas predominate in the middle division. Bronchogenic cysts comprise 7.5% of all mediastinal masses ( Fig. 19-16 ). They may be asymptomatic or have symptoms of airway obstruction or recurrent pulmonary infection ( Birmingham et al., 1993 ; Landsman et al., 1994 ). Bronchogenic cysts usually are next to the trachea or mainstem bronchi at the level of the carina, but they can also be intrapulmonary. They can produce sudden, life-threatening airway obstruction at any age. Lesser degrees of obstruction appear initially as wheezing, stridor, or unilateral obstructive emphysema.
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FIGURE 19-16 Magnetic resonance imaging of the chest; coronal section through the trachea and bronchogenic cyst (black arrows) located in the subcrinal area. The cyst is shown compressing the right mainstem bronchus (white arrow). (From Landsman IS, Bronert BJ, Wiener ES, Ford HR: Anesth Analg 79:803, 1994.) |
In the posterior division, enteric cysts and tumors of neurogenic origin (neuroblastoma, ganglioneuroma, neurofibroma) predominate. Enteric cysts and duplications are lined with secretory epithelium and can enlarge rapidly and cause dysphagia, ulceration, or bleeding. In rare cases they can ulcerate directly into the tracheobronchial tree. Neurogenic tumors are usually asymptomatic and detected on a routine chest radiograph, although they can be responsible for tracheobronchial compression, recurrent pneumonias, and, rarely, stigmata of pheochromocytoma.
Mediastinal infections and inflammation are less common today than in the past ( Campbell and Lilly, 1983 ). Modern antibiotic therapy dramatically reduced the incidence of suppurative mediastinitis caused by Staphylococcus and other organisms, whereas the incidence of tuberculosis and other similar infections in the general population has diminished. Although mediastinitis can result from extension of cervical node infections or hematogenous spread, the more likely cause is perforation of the trachea or esophagus. Foreign bodies can be responsible for perforation of the larynx, trachea, or esophagus; instrumentation of the trachea (endotracheal intubation or suction) or esophagus (esophageal dilation) can also be responsible.
Pneumomediastinum is an accumulation of air, usually in the superior anterior division. This occurs in trauma patients and as a result of mechanical ventilation, especially in newborns who undergo long-term ventilation and children with severe asthma. Pneumomediastinum is usually asymptomatic, but it may be responsible for tamponade and hypotension. These patients need urgent decompression by thoracostomy. Pneumomediastinum can be accompanied by pneumopericardium, which may need to be drained urgently as well. The intrathoracic pressure generated by pneumomediastinum can impede venous drainage of the head and result in increased intracranial pressure.
Anesthetic management of children with mediastinal diseases demands careful preoperative evaluation ( Mackie and Watson, 1984 ). The location and nature of the disease are crucial to both preparation and management. The airway is considered first ( Todres et al., 1976 ; Keon, 1981 ). If there is evidence of obstruction, the site and degree must be assessed. History and physical examination should focus not only on signs such as cyanosis and stridor but also on maneuvers or circumstances that change the signs. The practitioner should determine if sleep, excitement, position, movement of the head and neck, or coughing changes the degree of obstruction. Although chest radiographs and barium studies provide some information, CT scans are best at delineating the obstruction. These scans have the added advantage of demonstrating extension of infection or tumor into structures such as the pericardium. If a foreign body is responsible for the problem, the location and stability of the object are assessed.
Signs of lower airway disease can be caused by mediastinal tumors ( Sibert et al., 1987 ). Compression of the lower airways and lung tissue can be responsible for wheezing, atelectasis, obstructive emphysema, and recurrent pneumonias. This is important because wheezing caused by compression of lower airways and lung tissue usually does not respond to bronchodilators, nor will atelectasis caused by compression respond to chest physical therapy. Repeat chest radiographs or pulmonary function tests can help delineate the degree of functional impairment. In older, more cooperative children, maximal inspiratory and expiratory flow-volume loops obtained with the patient upright and supine can quantitate the functional degree of impairment and help distinguish fixed from variable obstructions ( Fig. 19-17 ).
|
FIGURE 19-17 Schematic tracing of maximum expiratory-inspiratory flow-volume curves. A, Variable upper airway obstruction caused by papillomatosis of the larynx. B, Variable central (intrathoracic) airway obstruction caused by tracheomalacia. C, Fixed-type obstruction caused by tracheal stenosis. (From Motoyama EK: Physiologic: Alterations in tracheostomy. In Myers EN, Stool SE, Johnson JT, editors: Tracheostomy. New York, 1985, Churchill Livingstone.) |
Cardiovascular involvement may be related to direct compression of the heart or of the great vessels. Echocardiography or CT scanning can delineate impingement. The important determination is assessment of functional impairment. If the child has arrhythmias, pulsus paradoxus, hypotension, or superior vena cava syndrome, the risk of general anesthesia increases dramatically.
Induction of anesthesia may remove compensatory efforts by the patient ( Neuman et al., 1984 ). The child's position, pattern of ventilation, or sympathetic tone while awake may have been responsible for barely maintaining adequate cardiopulmonary function ( Bray and Fernandes, 1982 ; Prakash et al., 1988 ) ( Fig. 19-18 ). In these situations, the anesthesiologist and surgeon must determine alternative approaches to the lesion ( Mackie and Watson, 1984 ). If the child has a better airway, easier ventilation, or less hypotension in one position, efforts are made to keep him or her in this position. Biopsy of accessible lesions under local anesthesia should be considered if there is significant cardiopulmonary compromise. In extreme cases, radiation therapy quickly shrinks the tumor mass, allowing a biopsy to be done later with less risk to the patient ( Piro et al., 1976 ). If general anesthesia is used, the surgeon should be present at induction and prepared for interventions such as passage of a rigid bronchoscope or immediate release of a pneumomediastinum via subxiphoid thoracostomy. Of utmost importance is that patients, family, pediatrician, and surgeon all understand the risk of cardiovascular and respiratory compromise that exists in performing tissue biopsies under general anesthesia ( Fig. 19-19 ).
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FIGURE 19-18 The effects of anesthesia on tracheal compression in a patient with a mediastinal mass. (From Prakash UBS, Abel MD, Hubmayr RD: Mediastinal mass and tracheal obstruction during general anesthesia. Mayo Clin Proc 63:1004, 1988.) |
|
FIGURE 19-19 Algorithm for mediastinal mass. |
Mask induction with a volatile agent and 100% oxygen is appropriate if there is concern about airway obstruction. The negative intrathoracic pressure of spontaneous breathing and any beneficial effect this has on maintenance of airway patency are preserved ( Sibert et al., 1987 ). In some cases, airway obstruction worsens with positive-pressure ventilation; it may be necessary to maintain spontaneous or assisted ventilation. Two important monitors during induction are breath sounds from the precordial stethoscope and continuous oxygen saturation monitoring from a pulse oximeter. Nitrous oxide is avoided in all cases of pneumomediastinum or obstructive emphysema and in patients who have significant / abnormalities from lung compression ( Mackie and Watson, 1984 ). The role of nitrous oxide in patients with asymptomatic bronchogenic cysts is unclear. Because these cysts are air filled, they may expand on exposure to nitrous oxide and cause airway compromise. In rare cases of severe airway impingement, intubation in the awake, sedated patient may be necessary to secure the airway safely for general anesthesia. If cardiac compression is of primary concern, narcotic-based anesthesia with or without ketamine for induction is a useful technique.
Thoracotomy or thoracostomy is usually the operative procedure performed in these patients. Major complications include massive blood loss, further obstruction or perforation of the airway, and lung compression ( Barash et al., 1976 ; Neuman et al., 1984 ). There continue to be sporadic reports of death during the induction and maintenance of anesthesia in children with mediastinal masses, emphasizing the need for meticulous preoperative evaluation and intraoperative care. From review of the 44 pediatric patients with mediastinal masses, Ferrari and Bedford (1990) noted that significant anesthesia-related problems occurred in the patients who were symptomatic before surgery. They noted that general anesthesia could be administered with the following caveats: spontaneous ventilation must be performed, induction of anesthesia should be in the sitting position, intravenous access should be in the lower extremity, and a rigid bronchoscope and experienced bronchoscopist must be available. The anesthesiologist not only must be prepared for each complication but also must notify the surgeon immediately if there is loss of airway, difficulty in ventilation, or sudden hypotension.
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Motoyama & Davis: Smith's Anesthesia for Infants and Children, 7th ed.
Copyright © 2005 Mosby, An Imprint of Elsevier
▪ UROLOGIC SURGERY
There is a wide range of surgical lesions that require the expertise of a pediatric urologist ( Box 19-5 ). Although the anesthetic requirements for the different surgical lesions vary, the preoperative anesthetic assessment focuses on several important considerations. First, does the child have a known syndrome that has multiple anesthetic considerations? Second, does the child have other congenital anomalies, such as cardiac abnormalities, that require evaluation? Last, does the child have signs or symptoms of any underlying renal insufficiency? (See Table 19-9 .) In general, renal failure is divided into acute and chronic components. Acute renal failure is the sudden loss of the kidney's ability to excrete water, electrolytes, and waste products in sufficient quantities to maintain the body's homeostasis. The causes of acute renal failure are numerous but are divided into four broad categories—prerenal, renal parenchymal, renal tubule, and obstructive. Regardless of its cause, management of acute renal failure is aimed at ensuring that the patient has an adequate circulating blood volume and avoiding fluid overload.
BOX 19-5
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Genitourinary Conditions Requiring Surgery During Infancy and Childhood |
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TABLE 19-9 -- Signs and symptoms of patients with renal insufficiency
|
System |
Signs and symptoms |
|
Cardiovascular |
Hypertension |
|
Increased cardiac output/high output failure |
|
|
Atherosclerosis/hyperlipidemia |
|
|
Pericarditis |
|
|
Variable increase in 2,3-diphosphoglycerate levels |
|
|
Pulmonary |
Hypoxemia |
|
Pulmonary edema |
|
|
Pleuritis |
|
|
Hematologic |
Anemia secondary to erythropoietin deficiency |
|
Anemia secondary to blood loss, decreased iron absorption, and folic acid deficiency |
|
|
Platelet dysfunction |
|
|
Decreased antithrombin III levels |
|
|
Increased factor VIII and fibrinogen |
|
|
Neurologic |
Irritability, confusion, anxiety, memory loss, encephalopathy, and psychosis |
|
Seizures, coma |
|
|
Peripheral neuropathy |
|
|
Gastrointestinal |
Anorexia, nausea, vomiting, gastroparesis |
|
Metabolic/endocrine |
Renal osteodystrophy secondary to hyperparathyroidism, hyperkalemia, hypocalcemia, metabolic acidosis, hypernatremia, and hyponatremia |
|
Infectious disease |
Hepatitis B or non-A, non-B hepatitis Cytomegalovirus and human immunodeficiency virus |
Congestive heart failure occurs when more than insensible fluid losses and urinary output are replaced. Although either a normal or reduced urinary output can occur with acute renal failure, with the onset of anuria or oliguria, hyperkalemia and hypocalcemia can occur. Hyperkalemia is the major life-threatening complication of acute renal failure and therefore must be treated immediately. Because of the kidney's inability to excrete cellular waste products, acidosis also develops in acute renal failure. Although most patients with acute renal failure have reversible conditions, some patients go on to develop chronic failure (see Chapter 4 , Regulation of Body Fluids and Electrolytes).
Chronic renal failure or end-stage renal disease (ESRD) results in a 95% loss of creatinine clearance. A 50% loss of nephrons generally results in no biochemical abnormalities and a glomerular filtration rate of about 80%. The biochemical manifestations of ESRD result in inability of the kidney to regulate water and electrolytes and to excrete acid waste products. Because the kidney is also an exocrine organ, progressive renal failure is also accompanied by abnormalities in the excretion of vitamin D, parathyroid hormone, and erythropoietin. ESRD, through its biochemical and hormonal mediators, affects all organ systems (see Chapter 4 ).
In addition to the pathophysiologic problems that accompany patients with renal and urologic abnormalities, the anesthesiologist must be cognizant of potential emotional difficulties that children have when faced with genitourinary surgery. Not infrequently, some of these patients have deep-seated emotional problems, and the anesthesiologist should be sensitive to their needs. Issues involving the psychologic preparation of the patient are explored in Chapter 7 , Psychological Aspects.
In the child with normal renal function, anesthesia for urologic surgery is similar to anesthesia for most other types of surgery. In patients with renal insufficiency, nephrotoxic drugs should be avoided or their dosage reduced. The differences in distribution and excretion of drugs that are renally excreted should be remembered. This primarily applies to neuromuscular blockers, because there is little evidence that the volatile agents are materially different in patients with renal insufficiency. There is a well-known risk of prolongation of action with morphine and, especially, meperidine, but the synthetic opioids are used more commonly in this population. Among the muscle relaxants, a delayed onset and slight resistance to vecuronium have been reported in renal failure patients ( Hunter, 1984 ), as well as delayed onset with rocuronium ( Driessen, 2002) . However, these differences are modest, even in children with complete renal failure.
Urologic procedures frequently require patients to be positioned in the lateral, prone, or lithotomy position. Each of these positions can be associated with compression-type injuries, as well as compromise of ventilation and venous return. Consequently, anesthetic management requires not only diligence to patient monitoring but also attention to appropriate patient positioning, padding, and rechecking of positioning.
▪ CYSTOSCOPY
Cystoscopy is commonly performed in children under the general anesthesia to evaluate abnormalities of the urethra, bladder, and ureters. This is a relatively brief procedure; however, positioning the patient away from the anesthesia machine, extending the anesthetic tubings and monitor cables, maintaining a possibly difficult airway at the far end of the operating table, and exposing the patient to a cold room and irrigating solutions may complicate the delivery of anesthesia. Mask inhalation anesthesia is usually satisfactory, and endotracheal intubation or laryngeal mask airway is not necessary beyond infancy, as long as a satisfactory airway can be maintained. It is important, however, to maintain a relatively deep plane of anesthesia before insertion of the cystoscope because the urethral stimulation may precipitate laryngospasm (Breuer-Lockhart reflex) ( Stehling and Furman, 1980 ). Regional anesthesia is infrequently used as the primary anesthetic for cystoscopy, but can be used for postoperative analgesia. However, most children experience little discomfort on awakening.
▪ CIRCUMCISION
Circumcision is the most frequently performed surgical procedure in the world ( Klauber and Sant, 1985 ). Most circumcisions are performed during the newborn period, and many are done without any anesthesia. However, there is increasing attention paid to providing analgesia for the procedure, including the use of the simple penile nerve block by obstetricians, family practitioners, and pediatricians (Maxwell, 1987 ; Howard et al., 1998 ). Simple techniques can significantly decrease cardiovascular and behavioral responses to pain in these neonates ( Holliday, 1999) . With increased education, especially at the resident level, there should be an increase in these techniques being used by primary care practitioners.
Beyond the newborn period, circumcision is usually performed under general anesthesia. Mask inhalation anesthesia with sevoflurane or isoflurane in nitrous oxide and oxygen is commonly used. A penile nerve block can be performed either immediately after anesthetic induction or at the end of the operation. It may be advantageous to place the block before the circumcision because the anesthetic requirement is decreased and emergence is more rapid. Caudal epidural anesthesia is also efficacious, although penile nerve block is preferred by some because less local anesthetic is given and less time is taken to perform the block. Others have suggested that the time, expense, and risk of caudal block are not justified for circumcision, because parenteral opioid administration is equally effective ( Martin, 1982 ).
A comparison of different modalities for analgesia, with a focus on caudal analgesia, found that although the need for rescue analgesia is reduced in the early postoperative period when caudal block is compared with parenteral analgesia, there is a paucity of data in the literature to accurately compare both the short- and long-term effectiveness of caudal block versus other modalities such as parental analgesia, penile block, or topical anesthetic gel or cream ( Allan, 2003) . This analysis points out a problem in analyzing almost all the work on analgesia for urologic procedures—there are insufficient studies available that compare all available modalities in a consistent, uniform manner, thereby allowing direct comparison of risks and benefits.
▪ HYPOSPADIAS REPAIR
Hypospadias occurs in approximately 8:1000 male births ( Belman, 1985 ). Associated anomalies that cause difficulties for the anesthesiologist are rare. Hypospadias is repaired either as a single-stage or a multistage procedure, depending on the complexity of the anatomic abnormality. The surgical procedure usually requires several hours, so most anesthesiologists prefer endotracheal intubation rather than mask anesthesia for patient safety and for convenience. The laryngeal mask airway (LMA) may also be useful in these procedures. Blood loss is usually not significant, and transfusion is rarely required. Induction of anesthesia can be achieved by any of the techniques commonly used in children. Intraoperatively, anesthesia can be maintained using either an inhalation or a balanced technique. General anesthesia combined with a conduction block provides excellent intraoperative conditions and postoperative pain relief.
Caudal epidural block may be the optimal choice because it provides complete intraoperative and postoperative analgesia. Penile block is less effective than caudal epidural anesthesia for postoperative analgesia after hypospadias repair, especially in cases of proximally located hypospadias ( Blaise and Roy, 1986 ). When only a distal penile hypospadias is present, penile nerve block may be as effective as caudal epidural anesthesia. In children under 1 year of age, a single caudal epidural injection of bupivacaine (0.25% with 5 mcg/mL epinephrine; 1.2 mL/kg) is administered after the induction of general anesthesia ( Hannallah, 1987) . Some practitioners prefer 0.2% or 0.125% bupivacaine to give greater volume with less risk of motor blockade. The caudal block is repeated at the end of the surgery if more than 1 hour has elapsed since the first caudal epidural injection. For children older than 1 year, it can be worthwhile to place a catheter for continuous caudal block using a commercially available epidural catheter kit. With the availability of smaller epidural catheters, a continuous infusion of local anesthetic may also be practical for younger patients (see Chapter 14 , Pediatric Regional Anesthesia).
▪ URETERAL REIMPLANTATION AND BLADDER NECK SURGERY
Reimplantation of one or both ureters is performed for treatment of vesicoureteral reflux whether it occurs congenitally or results from repeated urinary tract infections. The duration of the procedure may vary from 2 to 5 hours, so general anesthesia and endotracheal intubation are indicated. A caudal or lumbar epidural catheter can be used to provide supplemental regional anesthesia intraoperatively, minimizing the general anesthetic requirement as well as providing for postoperative analgesia and prevention of bladder spasm. The surgical procedure usually precludes the ability to measure urine output accurately. In those patients for whom the surgery is anticipated to take a long time, a central venous pressure catheter can be placed. For shorter surgical procedures, losses can be estimated by observation of the surgical field and vital signs. Serial hematocrit values should be measured whenever blood loss appears excessive. As with other urologic procedures, regional anesthesia via the caudal or epidural approach can be very useful for both intraoperative and postoperative pain relief.
▪ PRUNE-BELLY SYNDROME PROCEDURES
The prune-belly syndrome (Eagle-Barrett syndrome) occurs in 1:40,000 births, mostly in boys, and results from distal urinary tract obstruction that leads to multiple secondary organ dysfunction ( Jones, 1988 ). Figure 19-20 outlines the proposed sequence of events in the urethral obstruction malformation complex that leads to the classic manifestations, namely, abdominal muscular deficiency, renal dysplasia, excel abdominal skin, and cryptorchidism. Other variable features include colonic malrotation, persistent urachus, and lower limb abnormalities. Figure 19-21 shows the typical physical appearance of a child with prune-belly syndrome.
|
FIGURE 19-20 Developmental pathogenesis of early urethral obstruction sequence. (From Jones KL, editor: Smith's recognizable patterns of human malformation. Philadelphia, 1988, WB Saunders.) |
|
FIGURE 19-21 Infant with prune-belly syndrome. Note lax abdominal skin. (From Jones KL, editor: Smith's recognizable patterns of human malformation. Philadelphia, 1988, WB Saunders.) |
A classification system has been devised according to the severity of disease in prune-belly syndrome ( Woodhouse, 1982) . Group I children have severe renal disease, pulmonary hypoplasia, or both, which is incompatible with survival. Group II children are seen as neonatal emergencies with severe uropathy and urinary tract infection and require multiple corrective surgical procedures. Group III patients have minimal problems in the newborn period but are prone to infections in later childhood. The prognosis in group II and III children is good, with as many as half of the children in group II developing normally and exhibiting good renal function.
These patients have a depressed cough mechanism resulting from deficient abdominal musculature, so preoperative sedation is best avoided. Because aspiration is a risk, administration of an H2-antagonist (such as ranitidine) and sodium citrate may be indicated to raise gastric pH, and rapid sequence induction may be recommended. Controlled ventilation is necessary intraoperatively to prevent hypoventilation. Anesthesia can be maintained with inhalation agents or intravenous techniques, although muscle relaxation is usually unnecessary. Tracheal extubation should be performed only when the patient is awake and meets appropriate criteria. A review of 120 anesthetic cases suggested that intraoperative morbidity was rare, despite allowing spontaneous breathing in half of the cases ( Henderson, 1987) .
Postoperatively, respiratory infections occurred in approximately 7% of cases; one patient died from postoperative aspiration pneumonitis ( Henderson, 1987) . These patients require close observation and aggressive pulmonary toilet. Caudal, epidural, or spinal anesthesia in awake or mildly sedated patients may be useful for procedures such as cystoscopy or herniorrhaphy. After abdominal procedures, caudal or lumbar epidural administration of local anesthetic may be indicated to minimize postoperative pain. Postoperative mechanical ventilation may be required for patients who undergo extensive abdominal procedures or when significant pulmonary disease is present.
A wide variety of urologic abnormalities are found in prune-belly syndrome, including renal dysplasia, dilated and tortuous ureters, enlarged and dysfunctional bladder, urethral obstruction, and prostatic hypoplasia (Barrett and Mansoni, 1987). Despite severe urologic abnormalities, renal function may be well preserved. The surgical approach has become more conservative with the appreciation of the relatively good outcome in these patients. The standard surgical approach includes acceptance of the dilated upper urinary tract without extensive ureteral remodeling procedures and maintenance of adequate bladder drainage with urethral surgery (Barrett and Mansoni, 1987).
▪ REPAIR OF EXSTROPHY OF THE BLADDER
Exstrophy of the bladder is a rare anomaly, occurring in 1:30,000 births, most commonly in boys. This anomaly can be subdivided into classic exstrophy, cloacal exstrophy, and epispadias. Classic exstrophy is most common, with an absence of the anterior wall of the bladder and overlying abdominal wall, epispadias, and separation of the symphysis pubis. Many urologists prefer to perform a staged repair, with the initial stage scheduled during the newborn period. This allows approximation of the symphysis pubis without the need for iliac osteotomies. Multiple procedures are usually necessary in the first years of life to achieve complete repair. To formulate an appropriate anesthetic plan, including an accurate prediction of blood loss, the anesthesiologist must discuss the surgical plan preoperatively with the urologist.
During the newborn period, blood loss, evaporative losses, and third-space fluid losses can be excessive during bladder exstrophy repair. It is recommended that two intravenous catheters or a central venous catheter be placed before surgery. An arterial catheter may be useful for monitoring blood pressure and allowing the sampling of blood for measurement of glucose levels, hematocrit, and blood gas analysis. In addition, significant heat loss is common during these procedures, demanding close attention to temperature levels and active warming, usually through a forced-air heating system. A combined general anesthetic-epidural technique is increasingly popular for these cases, with the epidural catheter providing excellent analgesia into the postoperative period ( Wee, 1999) . Bupivacaine or ropivacaine is commonly used, but an opioid is not often added in the neonatal period because of the risk of respiratory depression, unless prolonged mechanical ventilation is anticipated. Postoperatively, careful attention must be focused on maintaining fluid and electrolyte homeostasis, as well as preventing anemia, hypotension, and hypoxia, as in any other case.
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Motoyama & Davis: Smith's Anesthesia for Infants and Children, 7th ed.
Copyright © 2005 Mosby, An Imprint of Elsevier
▪ BARIATRIC SURGERY
▪ OBESITY IN CHILDREN AND ADOLESCENTS
Obesity is the most common health problem facing U.S. children today. Data suggest that the prevalence of obesity continues to increase rapidly. Results from the National Health and Nutrition Examination Survey III reveal that approximately 14% of children in the United States are obese, as defined by body mass index (BMI) greater than the 95th percentile ( Centers for Disease Control and Prevention Update, 1997 ). The prevalence is increasing approximately 47% to 73% faster among black and Hispanic children than among non-Hispanic white children. As of 1998, the prevalence of obesity in children had increased to 21.5% among African Americans, 21.8% among Hispanics, and 12.3% among non-Hispanic whites ( Strauss and Pollack, 2001 ).
Childhood obesity has been defined variously by absolute weight, weight-for-height percentiles, percentiles of ideal body weight, triceps skinfolds, and BMI (weight in kilograms divided by height in meters squared). The most recent recommendations from the Centers for Disease Control and Prevention (CDC) suggest that BMI is the most appropriate and easily available method to screen for childhood obesity. Age and gender cutoffs for BMI have been published ( Kuczmarski et al., 2000 ). Patients with a BMI of greater than 30 are considered obese, and those with a BMI of greater than 40 are considered morbidly obese.
Although many of the adverse effects of childhood obesity may not become apparent for decades, even young children may suffer severe morbidity. Psychological problems include low self-esteem, self-consciousness, helplessness, and depression. Hypertension, hypercholesterolemia, and hyperinsulinism all occur in young, obese children, leading to coronary artery disease and diabetes in adulthood. Obese children may develop gallstones, hepatitis, obstructive sleep apnea, and increased intracranial pressure due to pseudotumor cerebri ( Strauss, 2002 ). The adverse effects of obesity in childhood are shown in Box 19-6 . These complications may result in the need for surgery (e.g., gallstones, slipped epiphysis, bariatric surgery) and complicate the anesthetic management during surgery (airway obstruction or reactivity, hyperglycemia, systemic or intracranial hypertension).
BOX 19-6
|
Adverse Effects of Obesity in Childhood |
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▪ PHYSIOLOGIC CONSIDERATIONS
Obesity is associated with many physiologic disturbances of concern to anesthesiologists. Work of breathing is increased, and fatty chest and abdominal walls decrease chest compliance. FRC and airway closing capacity are significantly reduced, causing hypoxemia due to intrapulmonary shunting. Exacerbations of hypoxemia due to sleep apnea may lead to pulmonary hypertension, cor pulmonale, and heart failure. A small number of morbidly obese patients have somnolence, cardiac enlargement, polycythemia, hypoxemia, and hypercapnia (Pickwickian syndrome). Morbidly obese patients with preoperative pulmonary dysfunction have higher morbidity following bariatric surgery but may subsequently have significant improvement in sleep apnea, gas exchange abnormalities, pulmonary hypertension, and cardiac function ( Sugerman et al., 1992 ).
Cardiac reserve is decreased in obese patients. Even normotensive morbidly obese patients have increased preload and afterload, increased pulmonary artery pressures, and elevated right and left ventricular stroke work compared with nonobese patients. The degree of cardiac abnormality correlates with the degree of obesity. Left ventricular dysfunction is often present in young, asymptomatic obese patients. Right ventricular failure is common in older patients ( Brodsky and Vierra, 2000 ). Weight loss, whether through diet or bariatric surgery, can reverse cardiac dysfunction and hypertension ( Jones, 1996 ). Hypertension is common among morbidly obese adolescents and adults.
The gastric contents of unpremedicated, nondiabetic, fasting obese patients (BMI > 30) without GER are not increased in volume or acidity compared with nonobese surgical patients ( Harter et al., 1998 ). However, morbidly obese patients (BMI > 40) do have large gastric volumes and low pH ( Vaughan et al., 1975 ). Morbid obesity is also associated with a high incidence of GER, with 70% of patients complaining of heartburn ( Hagen et al., 1987 ).
Other gastrointestinal abnormalities in morbidly obese patients include steatohepatitis, cirrhosis, and gallstones ( Clain et al., 1987) . Approximately 30% of patients who do not have gallstones at the time of bariatric surgery develop gallstones within 3 to 6 months after surgery, prompting many surgeons to perform a cholecystectomy at the time of the bariatric procedure.
Endocrine and genetic abnormalities are associated with obesity and short stature. Hirsutism, increased muscle mass, and acanthosis nigricans are associated with polycystic ovary syndrome. Obesity associated with mental retardation may signify a congenital syndrome such as Prader-Willi, Laurence-Moon-Biedl, or Cohen's syndromes. Females with short stature and obesity may be diagnosed with Turner's syndrome. Recurrent headaches, especially if associated with vomiting, may be caused by pseudotumor cerebri; papilledema may be seen on fundoscopic examination.
▪ BARIATRIC SURGICAL PROCEDURES
Gastric bypass and other types of bariatric surgery have been considered appropriate for selected adults with a BMI of 40 or of 35 in the presence of comorbid conditions ( Consensus Development Conference Panel, 1991 ; National Institutes of Health, 1998 ). Few data and no guidelines exist for bariatric surgery in adolescents. In 1975, Soper and others (1975) reported on 18 morbidly obese adolescents and young adults (age < 20 years) who underwent either gastric bypass or gastroplasty. The median weight loss was approximately 25% of body weight by 3 years following surgery. A similar report in 1980 described an average weight loss of 40 kg at 3 years and 26 kg at 5 years after surgery ( Anderson et al., 1980 ). Major early postoperative complications occurred in more than one third of the patients, including one death from an anastomotic leak. Since these early reports, the gastric bypass procedure has undergone significant modifications. Surgical stapling devices allow compartmentalization of the stomach without complete transection ( Kellum et al., 1998 ). “Long limb” gastric bypass has also been used in patients with BMI of greater than 50, with improved weight loss compared with conventional bypass procedures ( Brolin et al., 1992 ).
Strauss and others (2001) reported their results in 10 adolescents, aged 15 to 17 years, who underwent gastric bypass surgery. All patients were highly motivated and had demonstrated serious attempts at weight loss in diet and behavior modification programs. All adolescents were behaviorly and genetically normal and were more than 100% and 100 pounds above their ideal body weight. Obesity-related morbidities included sleep apnea, hypertension, vertebral fracture, and severe school avoidance. No perioperative complications were reported. Satisfactory weight loss was achieved in 9 of 10 patients, with a mean weight loss of greater than 50 kg. Late complications included protein-calorie and micronutrient malnutrition in one patient, an abdominal wall hernia requiring surgical repair in one patient, cholecystectomy in two patients, and small bowel obstruction requiring surgery in one patient.
Abu-Abeid and others (2003) reported their experience with 11 adolescents, aged 11 to 17 years, who underwent laparoscopic adjustable gastric banding (LAGB). Unlike gastric bypass operations, LAGB involves no anastomoses and no bypass of functional bowel, and the operation is reversible. The authors cited no perioperative or late complications; the mean decrease in BMI was from 46.6 to 32.1 kg/m2. One patient with heart failure and pulmonary hypertension had significant functional improvement during the 23-month follow-up period.
▪ ANESTHETIC MANAGEMENT
Preoperative Considerations
In preparation for surgery, a thorough history and physical examination should be performed. Review of systems is focused on medical complications of obesity shown in Box 19-6 . Medications taken for weight loss and other conditions are noted. Blood pressure and oxygen saturation should be recorded. Airway examination may reveal large tonsils and a small pharyngeal airway. Cardiac and lung auscultation may reveal signs of heart failure, pulmonary hypertension, wheezing, and low lung volumes. An electrocardiogram may show findings of cor pulmonale. An echocardiogram should be considered if cardiac dysfunction is suspected. In association with frequent urination, nocturia, and fatigue, blood glucose values may confirm the diagnosis of diabetes.
Administration of premedication should be followed by monitoring of oxygen saturation as ventilatory depression and airway obstruction may occur. An H2-receptor antagonist and metoclopramide may be given 60 to 90 minutes prior to anesthetic induction to decrease gastric volume and acidity. A nonparticulate oral antacid may be given immediately prior to induction.
Intraoperative Management
Many obese patients become hypoxemic in the supine position due to upper airway obstruction and diminished FRC. Elevating the head of the operating room table may diminish these changes. Noninvasive blood pressure measurements may be inaccurate, prompting the need for intra-arterial monitoring. Measurement of arterial blood gases at baseline and during general anesthesia is recommended, especially for lengthy surgeries. Because venous access may be limited, placement of a central venous catheter, although technically challenging, may be required. Meticulous attention to positioning and padding of the head, neck, and extremities is essential in order to prevent injury during surgery. Patients must be well secured to the operating room table in anticipation of the use of the Trendelenburg and reverse Trendelenburg positions as well as lateral rotation of the operating room table.
Because the risk of aspiration is high in morbidly obese patients, tracheal intubation should be performed when general anesthesia is administered even for brief procedures. Rapid sequence induction or awake fiberoptic-guided intubation should be performed to minimize the risk of pulmonary aspiration of gastric contents. Although most patients can be intubated with appropriate body positioning and direct laryngoscopy, two anesthesiologists and a “difficult airway” cart should be present during induction and intubation. Preoxygenation should be performed until the oxygen saturation had been 100% for several minutes. Patients should be ventilated with 100% oxygen with 10 to 15 mL/kg tidal volumes based on ideal weight. Moderate levels of positive end-expiratory pressure (PEEP) should be added to minimize airway closure, atelectasis, and oxygen desaturations. High levels of PEEP may depress cardiac output. Hypoxemia may occur due to placement of abdominal packs or retractors, gas insufflation during laparoscopic procedures, and use of the lithotomy or Trendelenburg positions. In extreme cases, the panniculus may need to be mechanically displaced to improve compliance and reduce physiologic shunt during surgery ( Wyner et al., 1981 ).
Drug and fluid administration should be based on ideal body weight. Doses of selected drugs may need to be increased compared with those administered to lean patients, however, due to increases in blood volume and cardiac output in the obese patient ( Brodsky and Vierra, 2000 ). Thiopental and midazolam have increased volumes of distribution in obese patients. Dosing regimens based on ideal body weight for propofol have been recommended ( Servin et al., 1993 ). A nerve stimulator should be used to guide the dosing of muscle relaxants and to monitor complete reversal of their effect. Excessive fat overlying the nerves may render surface electrodes ineffective, and needle electrodes may occasionally be required.
Although technically more difficult in obese patients, regional anesthetic techniques should be considered with or without general anesthesia. Local anesthetics may eliminate the need for muscle relaxants and their reversal. Even when general anesthesia is used in combination with regional anesthesia, decreased concentrations and doses of inhalation and intravenous agents allow for more rapid awakening and spontaneous airway control. Postoperative analgesia with epidural infusions facilitates improved pulmonary function.
Regional blocks can be difficult because important anatomic landmarks are often obscured. Long spinal or epidural needles are needed. The depth of insertion is difficult to predict; BMI alone is not an accurate predictor for depth of the epidural space ( Watts, 1993 ). Accordingly, the incidence of inadvertent dural puncture is increased in obese patients. Morbidly obese patients, however, have a decreased incidence of postdural puncture headache. Because the spread of local anesthetics is directly related to BMI, local anesthetic doses should be reduced by 20% to 25% for both epidural and subarachnoid blocks in obese patients ( Pitkanen, 1987 ; Taivainen et al., 1990 ). Insulated needles and a nerve stimulator may be helpful in identifying the appropriate nerves for peripheral nerve blocks.
Postoperative Care
Postoperative mechanical ventilation is infrequently needed except in the presence of significant cardiac disease, massive intraoperative fluid resuscitation, sepsis, or airway trauma during intubation. Tracheal extubation in hemodynamically stable, morbidly obese patients should be performed with the upper body elevated 30 to 45 degrees. The patient should be maintained in this position for transport in order to maximize FRC and oxygenation ( Vaughan et al., 1976 ). Supplemental oxygen should be administered via nasal cannula or mask for at least 3 days after abdominal or thoracic procedures (Taylor et al., 1985 ). Nasal continuous positive airway pressure (N-CPAP) or bilevel positive airway pressure (Bi-PAP) via nasal mask is used for patients with sleep apnea; these modalities may normalize breathing during sleep and prevent nocturnal oxyhemoglobin desaturation ( Series et al., 1992 ; Rennotte et al., 1995 ). Nasogastric tubes used during surgery must be removed before the application of N-CPAP or Bi-PAP. A potential complication of these therapies is gastric distention and disruption of bowel anastomoses, although this risk appears to be small.
Thromboembolism is a major cause of postoperative morbidity in obese surgical patients. Pulmonary emboli occur in as many as 5% of obese patients following laparotomy ( Brodsky and Vierra, 2000 ). The risk of thromboembolism can be reduced with heparin, pneumatic compression devices, or both ( Fasting et al., 1985 ). If an epidural catheter is to be used, it should be placed prior to initiation of heparin therapy and removed at least 12 hours after the last dose of heparin ( Horlocker et al., 2003 ).
Deep breathing, coughing, and early ambulation must be encouraged, and effective postoperative analgesia is essential. Patient-controlled analgesia with an intravenous opioid or epidural opioid with or without local anesthetic may be used. Analgesic drugs should be dosed according to ideal body weight. Vigilant monitoring for signs of excessive sedation and respiratory depression is required.
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Motoyama & Davis: Smith's Anesthesia for Infants and Children, 7th ed.
Copyright © 2005 Mosby, An Imprint of Elsevier
SUMMARY
The pediatric patient presenting for abdominal, genitourinary, or thoracic surgery spans the pathophysiologic spectrum. Both acute and elective clinical presentations, coupled with age-related nuances of the disease, dictate the perioperative anesthetic care of the patient. Advances in intraoperative techniques and postoperative pain management have enabled the surgical frontiers in those specialties to advance.
Copyright © 2008 Elsevier Inc. All rights reserved. - www.mdconsult.com
Motoyama & Davis: Smith's Anesthesia for Infants and Children, 7th ed.
Copyright © 2005 Mosby, An Imprint of Elsevier
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