Jeffrey L. Galinkin,
Uwe Schwarz,
Etsuro K. Motoyama
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Surgical Considerations, 509
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Anesthetic Considerations, 510
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Ex-Utero Intrapartum Therapy, 514
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Fetoscopic Surgery, 516
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Controversies, 518 |
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Summary, 519 |
Fetal surgery is an area of rapid and exciting growth. Ex-utero intrapartum therapy (EXIT), fetoscopic procedures, and open, midgestation procedures such as repair of myelomeningocele (MMC), congenital cystic adenomatoid malformations (CCAMs) of the lung, and sacrococcygeal teratoma (SCT) are now performed at multiple institutions around the world.
Fetal surgical techniques are based on years of animal and clinical research. In contrast, anesthesia for fetal surgery is based on clinical experience, case reports (Gaiser et al., 1997, 1999; [34] [35] O'Hara and Kurth, 1999; Rosen, 1999 ; Galinkin et al., 2000), and translation of responses to anesthetics in pregnant sheep (Motoyama et al., 1966, 1967; Palahniuk and Shnider, 1974 ; Biehl et al., 1983a, 1983b; Gregory et al., 1983; Bachman et al., 1986; Sabik et al., 1993). This chapter provides a review of the maternal and fetal anesthetic considerations for each type of fetal surgical procedure.
▪ SURGICAL CONSIDERATIONS
Surgical intervention is considered when a fetus presents with a congenital lesion/condition that can compromise or disturb cardiovascular function or cause severe postnatal morbidity. Surgery is only performed when the risk to the mother is low and the risk of death or severe disability to the fetus outweighs no intervention. Contraindications for these procedures are medical conditions in the mother precluding surgery or lethal/disabling genetic defects in the fetus.
Fetal surgery can be divided into three distinct procedure groups ( Table 15-1 ). Midgestation hysterotomy is performed on fetuses with well-defined congenital lesions. Surgery on the fetus is performed between 18 and 26 weeks through a hysterotomy. For these procedures, the fetus is exteriorized for surgical intervention and then placed back in the uterus to mature. Correction of these lesions is expected to either improve fetal survivability or enhance postgestation quality of life. If left untreated, these lesions result in severe disability or death.
TABLE 15-1 -- Surgical approaches to fetal lesions: Timing and cause for treatment
|
Surgical Approach |
Fetal Lesion/Anomaly |
Reason for Treatment |
Gestational Age |
|
Open/hysterotomy |
Congenital cystic adenomatoid malformation |
Hydrops fetalis, lung hypoplasia |
18 to 25 wk |
|
Myelomeningocele |
Amniotic fluid neurotoxicity |
22 to 26 wk |
|
|
Sacrococcygeal teratoma |
Hydrops fetalis |
18 to 25 wk |
|
|
Ex-utero intrapartum therapy |
Congenital or iatrogenic high airway obstruction |
Secure airway |
Near term |
|
Giant fetal neck mass |
Secure airway, resect mass |
Near term |
|
|
Fetoscopic surgery |
Twin—twin transfusion |
Impending fetal death, hydrops fetalis |
Midge stati on |
|
Twin reversed arterial perfusion sequence |
Impending fetal death, hydrops fetalis |
Midge stati on |
|
|
Bladder outlet obstruction |
Hydronephrosis and renal hypoplasia |
Midge stati on |
Ex-utero intrapartum therapy (EXIT) procedures are hysterotomy-based procedures performed at or near term on fetuses with expected immediate postgestation airway or oxygenation compromise. Surgery on the fetus is done after hysterotomy but before cord clamping. Surgeons then assess the infant's airway through bronchoscopy and secure the airway via an endotracheal tube or tracheotomy before complete airway obstruction or ventilation failure. During this time, the fetus is maintained by placental transfer of oxygen and carbon dioxide.
Fetoscopic surgery is a minimally invasive technique that uses small-diameter trocars and laparoscopes placed percutaneously to access the uterus. This technique is most commonly used for the evaluation and treatment of twin reverse arterial perfusion sequence, twin-twin transfusion syndromes, amniotic band syndrome, and bladder outlet obstruction. Surgical devices such as electrocautery and lasers are used to ablate or cauterize vessels or tissue during these procedures. This technique is considered when fetal death or severe fetal morbidity is imminent or traditional therapeutic measures (e.g., amnioreduction) have failed.
▪ OPEN FETAL SURGERY
Open fetal surgeries are usually performed on the midgestation fetus with MMC, CCAM, or SCT. To qualify as a surgical candidate, a mother must undergo extensive medical and psychosocial screening, have a fetus with disease that merits intervention, and be at low maternal risk for anesthesia and surgery.
Fetal surgery is performed through a low transverse abdominal incision. The uterus is exteriorized through this incision. Placental location is determined by ultrasonography, and a wide uterine incision is created with a specially designed absorbable stapler (Bond et al., 1989). This stapler allows performance of a “bloodless hysterotomy.” After hysterotomy, the fetus or fetal part is exteriorized for fetal surgery. Once the defect has been repaired and returned to the uterus, a watertight two-layer uterine closure is made (Bianchi et al., 2000). Warm saline with oxacillin is infused into the uterus to maintain uterine volume and decrease postoperative contractions. The skin is then closed and the maternal operation is completed.
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
▪ ANESTHETIC CONSIDERATIONS
▪ MATERNAL ANESTHETIC CONSIDERATIONS
Regional anesthesia is usually the technique of choice for obstetric anesthetic practice, but because the uterine relaxation required for fetal surgery is best provided by a high concentration of potent volatile agents, general anesthesia is the technique of choice for fetal surgery.
The maternal physiologic changes that occur during pregnancy contribute to increased anesthetic risk for both the mother and fetus. Pregnant patients undergoing general anesthesia are at increased risk for aspiration pneumonitis. Pregnancy decreases lower esophageal sphincter tone due in part to altered anatomic relationship of the esophagus to the diaphragm and stomach. In addition, pyloric displacement and increased gastric acid production result in an increased intragastric pressure. Rapid sequence induction is always performed for endotracheal intubation.
Pregnancy affects maternal pulmonary function. The cephalad encroachment of the gravid uterus reduces functional residual capacity, particularly the volumes of the lower lobes, and oxygen consumption increases to meet the increased demands of both the mother and the fetus. These factors increase the risk of hypoxia during rapid sequence induction. Decreases in capillary oncotic pressure and increases in capillary permeability increase the risk of pulmonary edema, especially postoperatively when magnesium sulfate is used for tocolysis.
The cardiovascular system is affected by pregnancy. A decrease in preload during supine positioning (supine hypotension syndrome), due to compression of the inferior vena cava, can cause maternal hypotension and fetal hypoxia. It is important to position the mother with left uterine displacement to displace the uterus from the inferior vena cava.
The parturient's central nervous system is also affected by pregnancy. During pregnancy, sensitivity to inhaled anesthetics is increased; minimum alveolar concentration (MAC) is significantly decreased; and sensitivity to muscle relaxants is also increased (Palahniuk et al., 1974; Strout and Nahrwold, 1981 ; Gin and Chan, 1994 ; Chan and Gin, 1995 ; Chan et al., 1996). Lower doses of volatile anesthetics and muscle relaxants are needed for surgery.
▪ FETAL ANESTHETIC CONSIDERATIONS
The primary concern of anesthetic management is the maintenance of placental circulation and fetal cardiovascular stability. The combination of immature organ function and cardiovascular compromise predisposes the fetus to anesthetic difficulty. The fetal cardiovascular system is less able to compensate for hypoxia and hypovolemia than is that of a full-term infant. Lacking a functional pulmonary system to increase oxygen tension, the fetus relies on increased umbilical blood flow and cardiac output and blood flow redistribution to improve oxygen delivery to the vital organs. The Starling curve is shifted down in a fetus compared with a neonate, resulting in less cardiac output for a given stroke volume ( Fig. 15-1 ). Cardiac output is more dependent on heart rate. Because of high vagal tone and low baroreceptor sensitivity, the fetus responds to stress with a decrease in heart rate.
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FIGURE 15-1 Stroke volume versus end-diastolic volume in the adult, neonate, and fetus. |
Fetal circulating blood volume is relatively low; the midgestation fetus has an estimated fetoplacental blood volume of 50 to 70 mL (110 mL/kg) (Nicolaides et al., 1987; MacGregor et al., 1988). A small amount of surgical blood loss can precipitate hypovolemia. Inhaled anesthetics also destabilize the fetal cardiovascular system by causing direct fetal myocardial depression, vasodilation, and changes in arteriovenous shunting ( Palahniuk and Shnider, 1974 ; Biehl et al., 1983; Bachman et al., 1986; Sabik et al., 1993).
Because of incomplete myelination and less synaptic activation, the fetus is more sensitive to inhaled agents. This increased sensitivity results in a decreased MAC compared with pregnant adults (Gregory et al., 1983; Bachman et al., 1986). Sensitivity to analgesics and muscle relaxants is also greater in the fetus compared with the neonate.
Fetal cutaneous heat and evaporative losses require warm ambient temperatures during fetal exposure. Limiting fetal surgical time and the use of warm irrigation fluids can prevent hypothermia.
Altered coagulation factors predispose to bleeding and cause difficulty in surgical hemostasis during fetal surgical manipulation. The small blood volume of the fetus compounds this problem. Fetal hemoglobin can be assessed intraoperatively with central or percutaneous blood samples.
▪ UTEROPLACENTAL ANESTHETIC CONSIDERATIONS
Uterine and umbilical blood flow and placental barriers to diffusion influence fetal oxygen delivery. Maternal systemic blood pressure and myometrial tone directly correlate with uterine artery blood flow. Volatile anesthetics decrease myometrial tone and tend to decrease maternal blood pressure and maternal placental blood flow. This can result in a decrease in fetal oxygenation ( Heymann and Rudolph, 1967 ; Luks et al., 1996; Parry et al., 2001 ). Umbilical artery blood flow is influenced by fetal cardiac output and vascular resistance, both intrinsic and extrinsic (e.g., compression by a “nuchal cord”). Maintenance of a patent umbilical artery and a near-baseline maternal arterial pressure are critical (maternal systemic pressure within 10% of baseline).
Studies in fetal lambs have shown that fetal-placental blood flow is significantly affected by maternal arterial Pco2 and pH. Maternal hypocapnea markedly reduces umbilical venous blood flow and results in fetal hypoxia and metabolic acidosis (Motoyama et al., 1966). In contrast, maternal hypercapnea (Paco2 > 60 mm Hg) and acidosis (pH < 7.3) increase umbilical venous blood flow and increase umbilical venous and fetal carotid Po2 above the physiologic ranges (Motoyama et al., 1967). The results of this study also show that with the same maternal Pco2, maternal hyperoxia was associated with an increase in fetal carotid Po2(Rivard et al., 1967). These findings in animal studies were corroborated in a clinical study in 38 parturient women during cesarean section under general inhalation anesthesia (Peng et al., 1972). In this study, the group of parturients, whose arterial Pco2 (Paco2) was kept between 30 and 50 mm Hg with the addition of 2% CO2, had significantly higher umbilical (postductal) arterial Po2and lower fetal base deficit than those who were ventilated with the equivalent ventilator setting but without added CO2 and with lower Paco2 (20 to 30 mm Hg). There was a significant correlation between the maternal Paco2 and umbilical arterial Po2 as well as fetal base deficit (Peng et al., 1972). Maternal hypocapnia should be avoided during maternal-fetal procedures. Possible efficacy of hypercapnea to enhance fetoplacental circulation should be explored in the future.
Control of myometrial tone by general inhalation anesthesia is necessary for open fetal surgery to provide optimal operative exposure. Epidural anesthesia alone does not provide uterine relaxation. Epidural anesthesia may help prevent premature labor in the postoperative period (Tame et al., 1999). Magnesium sulfate, terbutaline, nifedipine, and indomethacin are also used alone or in combination to maintain uterine quiescence in the postoperative period.
▪ PREOPERATIVE EVALUATION AND PREPARATION
In the preanesthetic evaluation, maternal and family history of anesthetic problems, airway examination, maternal size/weight, placental location, and fetal cardiovascular function are all examined. The fetus is evaluated by ultrasonography, echocardiography, magnetic resonance imaging (MRI), and karyotype analysis. The mother must be able to comply with the intensive demands postoperatively including bed rest and compliance with medications. When the decision for surgery is made, a multidisciplinary team consisting of surgery, anesthesia, obstetrics, genetics, social work, and nursing personnel meet to discuss the plan and obtain consent.
Patients are admitted to the hospital on the day of surgery. In preparation for surgery, the operating room is warmed to 80°F (26.7°C), and type-specific packed red blood cells (for the mother) and O-negative packed red blood cells (for the fetus) are made available. Monitors include two pulse oximeters (maternal and fetal) and an arterial pressure transducer. Epinephrine 10 mcg/kg, atropine 20 mcg/kg, vecuronium 0.2 mg/kg, and fentanyl 20 mcg/kg are prepared in a sterile manner in 1-mL syringes for possible fetal intramuscular administration. After ensuring the nothing-by-mouth (NPO) status of the mother, a single large-bore intravenous catheter is inserted. Sodium bicitrate 30 mL PO and metoclopramide 10 mg IV are administered to the mother to decrease the risk of aspiration pneumonitis. An indomethacin suppository is administered for postoperative tocolysis. A lumbar epidural catheter is inserted and tested with lidocaine 1.5% with epinephrine 1:200,000. The parturient is then positioned on her left side or the operating room table is tilted to the left side to minimize supine hypotension syndrome.
▪ INTRAOPERATIVE MANAGEMENT
Rapid sequence induction using intravenous sodium thiopental or propofol and succinylcholine is performed followed by tracheal intubation. General anesthesia is maintained with 0.5 MAC volatile anesthetic (isoflurane or desflurane) and 50% nitrous oxide. A radial arterial catheter, second intravenous catheter, nasogastric tube, and Foley catheter are inserted. Fetal status is monitored with sterile intraoperative echocardiography. Intravenous fluid is restricted to 500 mL total to reduce the risk of postoperative pulmonary edema.
Open hysterotomy procedures require low uterine tone to maintain fetal perfusion and optimize fetal exposure. Before the maternal skin incision, nitrous oxide is turned off to improve fetal oxygenation (Parpaglioni et al., 2002), and the inhalation agent is increased to 2.0 MAC to provide uterine relaxation and fetal anesthesia by the time of uterine and fetal incision. Ephedrine 5 to 10 mg IV or phenylephrine 1 to 2 mcg/kg IV is administered as necessary to maintain maternal systolic blood pressure within 10% of baseline.
Fetal anesthesia and analgesia are provided by a combination of placental passage of volatile anesthetics and intramuscularly administered opioids. Equilibration between mother and fetus with isoflurane (Biehl et al., 1983) ( Fig. 15-2 ) and desflurane ( Schwarz et al., 2003 ) ( Fig. 15-3 ) reaches approximately 70% and 50% of maternal levels, respectively, in 1 hour. Before fetal incision, the fetus receives fentanyl 20 mcg/kg IM to supplement the anesthesia and provide postoperative analgesia.
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FIGURE 15-2 Isoflurane versus time for mother and fetus during maternal anesthesia. |
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FIGURE 15-3 Desflurane versus time for mother and fetus during maternal anesthesia. |
Fetal well-being is assessed via both direct and indirect methods. For procedures in which a fetal extremity is accessed (CCAM and SCT resections), fetal arterial saturation is monitored by pulse oximetry. The pulse-oximetry probe is placed on the fetal hand and wrapped with foil to decrease ambient light exposure ( Fig. 15-4 ). Normal fetal arterial saturation is 60% to 70% (Johnson et al., 1991); during fetal surgery, values greater than 40% represent adequate fetal oxygenation. Echocardiography is also used to monitor fetal heart rate and stroke volume. Fetal distress, manifested by bradycardia, decreased saturations, or decreased stroke volume, is often a result of partial umbilical cord occlusion. Fetal arterial or venous blood gas samples may be obtained by the surgeons percutaneously or through umbilical or central vessel puncture to help guide therapy during periods of fetal distress. Warm, fresh O-negative blood can be administered to the fetus to correct anemia through a percutaneous peripheral venous line placed intraoperatively.
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FIGURE 15-4 Fetal hand with pulse-oximetry probe. |
After closure of the uterus, the anesthetic is converted to a regional technique. As the final stitches are placed in the uterus, the volatile anesthetic is decreased to 0.5 MAC and the epidural catheter is dosed with local anesthetic and opioid (15 to 20 mL bupivacaine 0.25% and morphine 0.05 mg/kg). Tocolysis is instituted via a loading dose of magnesium sulfate 6 g IV followed by a magnesium sulfate IV infusion at 2 to 3 g/hr. The patient's trachea is extubated after skin closure, and she is then transferred to the obstetric floor for postoperative care.
▪ POSTOPERATIVE MANAGEMENT
Key goals for postoperative management include prevention of premature labor and maintenance of maternal comfort. Magnesium sulfate is the drug of choice in the early postoperative period (18 to 24 hours) for tocolysis while a patient-controlled epidural infusion is used for analgesia. A well-functioning epidural analgesia may assist in the prevention of preterm labor (Tame et al., 1999). Indomethacin is continued for 48 hours postoperatively; fetal ductus arteriosus diameter is monitored daily. After discontinuation of the epidural block and magnesium sulfate, the first line of tocolysis is oral nifedipine. If this fails, terbutaline is administered via a subcutaneous route through an external pump. Bed rest is recommended for the remainder of the pregnancy. The patient is an obligate cesarean section for both this delivery and all subsequent deliveries due to the high uterine incision needed for these surgeries (Bianchi et al., 2000).
▪ SURGICAL LESIONS ELIGIBLE FOR OPEN FETAL SURGERY
Myelomeningocele
A myelomeningocele (MMC) is a lumbosacral vertebral lesion that occurs when the dorsal portion of the spinal cord is not covered with skin ( Fig. 15-5 ). The cord is exposed to the caustic amniotic fluid, causing a chronic chemical exposure. The open spinal cord is also exposed to traumatic injury via mechanical compression. The combination of these two exposures is thought to be the underlying mechanism for progressive and irreversible damage to the spinal cord seen in these patients (Meuli et al., 1997). The long-term consequences of this lesion include paraplegia, hydrocephalus, incontinence, sexual dysfunction, skeletal deformities, and impaired mental development.
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FIGURE 15-5 Surgical exposure of a fetal myelomeningocele in a 22-week-old fetus. |
Maternal serum α-fetoprotein screening identifies more than 80% of fetuses with MMC by midgestation ( Brock and Sutcliffe, 1972 ). Direct visualization of the fetal spine on ultrasonography can also aid in prenatal screening for fetuses greater than 16 weeks gestation. Other sonographic findings associated with MMC include frontal bone scalloping (lemon sign), abnormality of the cerebellum (banana sign), Chiari II malformation, hydrocephalus, microcephalus, and encephalocele.
The rationale for intrapartum midgestation MMC repair is based on the observation that lower extremity function during early pregnancy is progressively lost later in gestation (>20 weeks). In animals, intrauterine repair of MMC preserves peripheral neurologic function ( Michejda, 1984 ; Heffez et al., 1990, 1993; Meuli et al., 1995a, 1995b; Hutchins et al., 1996) and decreases the incidence of hindbrain herniation (Chiari type II malformation) (Paek et al., 2000). A retrospective review of clinical experience confirmed these findings in humans (Adzick et al., 1998; Tulipan et al., 1998; Bruner et al., 1999a, 1999b; Sutton et al., 1999). Furthermore, intrauterine repair of MMC (fetal lesions below L-3) appeared to substantially reduce the incidence of shunt-dependent hydrocephalus compared with conventional treatment, even when lesion level was taken into account (Tulipan et al., 2003).
The surgical experience of fetal MMC repair is promising, but the varying natural history, lack of accurate prenatal indicators of neurologic function, and absence of matched controls and long-term follow-up hamper the risk/benefit assessment of prenatal intervention (Sutton et al., 1999). A multicenter long-term prospective randomized placebo-controlled trial began in 2003 to assess the overall usefulness of these procedures.
Congenital Cystic Adenomatoid Malformation
Congenital cystic adenomatoid malformation (CCAM) is a rare lesion characterized by a multicystic mass of pulmonary tissue with a proliferation of bronchial structures (Stocker et al., 1977; Miller et al., 1980). A CCAM results either from a failure of maturation of bronchiolar structures in early gestation (Stocker et al., 1977; Miller et al., 1980; Shanji et al., 1988) or as a focal pulmonary dysplasia (Leninger and Haight, 1973 ). Associated malformations include genitourinary anomalies, such as renal agenesis or dysgenesis; cardiac anomalies, including truncus arteriosus and tetralogy of Fallot; jejunal atresia; diaphragmatic hernia; hydrocephalus; and skeletal anomalies.
CCAMs can be detected on ultrasonography at as early as 16 weeks gestation and are the most common type of fetal thoracic masses detected in this manner. The majority of CCAMs are diagnosed before 22 weeks' gestation (Adzick et al., 1985) and represent a broad spectrum of clinical severity. They may enlarge significantly, may remain the same size, or may disappear in the prenatal period (Adzick et al., 1985, 2003; Rice et al., 1994). When sufficient cardiac and great vessel compression lead to cardiac failure, these lesions cause fetal death. Cardiac failure often manifests as hydrops fetalis, a condition consisting of polyhydramnios, ascites, skin edema, and effusions of the pericardial or pleural space.
A CCAM typically presents as a lobular lung lesion ( Fig. 15-6 ). Rare cases have been reported of multilobar involvement of one lung or of bilateral lesions. Intrapartum fetal surgery for thoracoamniotic shunting (in cases with a large predominant cyst) or lung lobectomy, with complete resection of the CCAM, is the treatment of choice for this disease process when fetal hydrops is present or if conservative treatment fails. The mortality rate for fetal lobectomy is about 50% (Adzick et al., 2003). In cases where there is extensive involvement of the entire lung, resection of multiple lobes or pneumonectomy may be necessary. Term or near-term fetuses with CCAMs that may not survive delivery secondary to mass size or expected fetal compromise at birth may qualify for an EXIT procedure with resection of the mass during EXIT with or without postoperative transfer to extracorporeal membrane oxygenation.
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FIGURE 15-6 Surgical exposure of a fetal cystic adenomatous malformation. |
Sacrococcygeal Teratoma
A sacrococcygeal teratoma (SCT) is a neoplasm that can be composed of tissues of all three germ layers or multiple foreign tissues lacking organ specificity ( Fig. 15-7 ). It occurs in approximately 1:35,000 live-births ( Schiffer and Greenberg, 1956 ; Bale, 1984 ). Females are four times more likely to be affected as males, but development of malignancy is more often observed in males (Abbott et al., 1966;Conklin and Abell, 1967 ; Carney et al., 1972; Altman et al., 1974). Included in the differential diagnosis of SCT are lumbosacral myelomeningocele, neuroblastoma, glioma, hemangioma, neurofibroma, cordoma, leiomyoma, lipoma, melanoma, and other tumors and malformations of the sacrococcygeal region.
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FIGURE 15-7 A sacrococcygeal teratoma at midgestation during fetal surgery. |
Prenatally diagnosed SCT is different from neonatal SCT. The mortality rate for SCT diagnosed in the antenatal period is 5%, whereas the mortality rate for SCT diagnosed in the perinatal period is close to 50% (Bond et al., 1990; Flake, 1993 ). Malignant invasion is the primary cause of death in neonatal SCT, but this occurs rarely in utero (Graf et al., 1998). High-output cardiac failure is the primary cause of death from fetal SCT secondary to a “vascular steal” phenomenon by the tumor (Bond et al., 1990). Hydrops fetalis occurs in 10% of fetal SCTs and results in fetal death if left untreated (Langer et al., 1989).
SCTs can also lead to a potentially devastating maternal complication—the maternal mirror syndrome (Ballantine syndrome) (Kuhlmann et al., 1987). In this syndrome, the mother experiences progressive symptoms suggestive of preeclampsia, including vomiting, hypertension, peripheral edema, proteinuria, and pulmonary edema, due to the release of placental vasoactive factors or endothelial cell toxins from the edematous placenta. This syndrome can be reversed only by delivering the child and the placenta but not by removing the SCT.
Prenatal diagnosis is made by ultrasonography or MRI and has been reported as early as 14 weeks' gestation (Holzgreve et al., 1985). Color flow Doppler ultrasonography of large vascular tumors can demonstrate markedly increased distal aortic blood flow and shunting of blood away from the placenta and toward the tumor.
The rationale behind the prenatal resection of SCT in utero is the devastating outcomes for these fetuses when the tumor is complicated by placentamegaly and hydrops fetalis. Currently, efforts are aimed at developing a minimally invasive approach to reverse the “vascular steal” physiology via coagulation of the tumor's major blood supply (Westerburg et al., 1998; Paek et al., 2001).
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
▪ EX-UTERO INTRAPARTUM THERAPY
The EXIT procedure is used to achieve a patent fetal airway, to resect pulmonary masses, or to ensure adequate fetal oxygenation for diseases in which the fetus has a congenital or an acquired obstructive airway lesion. These procedures require general anesthesia to relax the uterus and anesthetize the fetus. EXIT procedures culminate with the delivery of the fetus. The newborn who underwent this surgery may require additional surgery and have special anesthetic needs.
▪ PREOPERATIVE MANAGEMENT
Maternal preparation for EXIT is similar to that for open fetal surgery. Most of these patients are followed for an extended period of time because the fetal lesions were discovered on prenatal ultrasounds. Early prenatal diagnosis allows time for counseling and maternal and fetal testing that these patients require.
Anesthetic preparation is the same for the EXIT as for the open procedure with two notable exceptions: tocolytics are not used, and one additional operating room is available for direct postdelivery care and possible surgery of the newborn. Tocolytics are unnecessary because the procedure ends in delivery. Resuscitation equipment, neonatologists, and a second operating room are all made available for postdelivery care of the neonate.
▪ INTRAOPERATIVE MANAGEMENT
The risks of aspiration and supine hypotensive syndrome are high in the term gestation mother with a large gravid uterus. After epidural placement, rapid sequence induction is performed, followed by orotracheal intubation. A second intravenous catheter, a nasogastric tube, and a Foley catheter are placed. The second intravenous catheter is placed in case the patient requires volume resuscitation for acute blood loss after delivery of the fetus. A maternal arterial cannula is placed when a fetus has end-stage disease manifesting as fetal hydrops due to lability of maternal blood pressure during these cases (unpublished observation).
Anesthesia for the EXIT is delivered via an inhalation-based technique. Sub-MAC concentrations (0.5 MAC) of volatile agents are used before maternal skin incision, and a high-level inhaled agent is used thereafter. Ephedrine and phenylephrine are used for maternal blood pressure maintenance. For rapid maternal and neonatal emergence after delivery, the preferred inhaled agent is desflurane because of its low blood-gas solubility.
During hysterotomy, it is important for the surgeons to only partially expose the fetus and to maintain the uterine volume at an appropriate level so that placental perfusion is maintained. Maternal hyperventilation should be avoided because maternal hypocapnia causes fetal placental vasoconstriction and fetal hypoxia (Motoyama et al., 1967; Peng et al., 1972). Fentanyl 20 mcg/kg IM is administered to the fetus to supplement fetal analgesia and provide postoperative analgesia. Fetal status is closely monitored via a pulse oximeter, sterile echocardiography, and visual inspection. Fetal blood gases are obtained as needed, and fresh O-negative blood is administered if necessary. Direct laryngoscopy and intubation of the fetus are performed by either the surgeons or the anesthesiologist. If the fetus cannot be intubated, partial resection of an obstructive lesion, tracheotomy, or both are performed by the surgeons. After the airway is secured and adequate fetal oxygenation with manual ventilation is ensured, the umbilical cord is clamped and the fetus is delivered.
After the delivery, it is important to quickly reverse uterine relaxation. Volatile agents are decreased after cord clamping, and the epidural catheter is dosed with local anesthetic and an opioid analgesic. Due to the anesthetic-induced uterine relaxation, uterine atony and significant blood loss are risks. The timing of cord clamping with respect to administration of oxytocin, methergine, and prostaglandin F2αmust be coordinated between anesthesiologist and surgeon. Blood loss is monitored, and cross-matched blood is administered if needed. Epidural analgesia is used for postoperative analgesia, and the trachea is extubated after surgical closure.
▪ POSTDELIVERY/POSTOPERATIVE MANAGEMENT
After surgery/delivery, there are two patients for which to care. The mother is brought to a postpartum ward. The immediate disposition of the newborn infant is based on surgical need—a second operating room should be available in case further surgery is needed, such as for excision of a cervical teratoma. If surgery is not required immediately, a neonatology team resuscitates and transports the neonate to intensive care.
When further surgery is necessary, there are several considerations unique to the immediate newborn. First, it is essential to dry and clean the newborn to minimize evaporative heat loss and because of the inherent difficulty of monitors sticking to the newborn. Second, the immediate newborn has a lower MAC requirement. Third, these infants have a transitional cardiac circulation, which can be compromised by surgical manipulation of adjacent structures (see Chapter 3 , Cardiovascular Physiology). Finally, the neonatal lungs are fluid filled, have low compliance, and are extremely susceptible to lung injury from hyperdistention (volutrauma). Vigorous resuscitation with high inflation pressure and volume can cause damage to the neonatal lung and adversely affect gas exchange ( Jobe and Ikegami, 2001 ).
▪ SURGICAL LESIONS ELIGIBLE FOR EX-UTERO INTRAPARTUM THERAPY
Lymphangioma (Cystic Hygroma)
A lymphangioma is a benign malformation composed of dilated cystic lymphatic tissue that most commonly occurs in the soft tissue of the neck, axilla, thorax, and lower extremities ( Isaacs, 1997 ). The lesions vary in size from tiny subepidermal skin bubbles to large cystic masses filled with fluid, commonly referred to as cystic hygromas when presenting in the neck ( Fig. 15-8 ).
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FIGURE 15-8 A fetus undergoing ex-utero intrapartum therapy (EXIT) procedure for cystic hygroma. |
Lymphangiomas are divided into two groups. The first group is identified by prenatal ultrasound examination in the second trimester; 60% of these fetuses have chromosomal abnormalities often associated with other structural anomalies and a high mortality rate (Cohen et al., 1989; Welborn and Timm, 1994 ). These cystic hygromas are usually situated at the posterior cervical triangle; associated structural anomalies include cardiac defects, hydronephrosis, neural tube defect, cleft lip and palate, multiple pterygium syndrome, skeletal anomalies, imperforate anus, and ambiguous genitalia.
The second group is diagnosed either at birth, as an isolated finding in an otherwise healthy infant, or as a new ultrasonographic finding in the third trimester. These lesions are a different entity than those seen in the first group. Lymphangiomas in these fetuses are located in the anterior cervical triangle, are not associated with other birth anomalies, and generally do not require emergent surgical resection.
The only fetal procedure that is indicated for large cystic hygromas is an EXIT procedure. The EXIT procedure allows the airway to be secured and a surgical resection of the cystic hygroma to be performed if immediately necessary. Although cyst aspiration can help to secure a fetal airway at birth of an unrecognized cystic hygroma, there are little data to support the use of in utero decompression of the fetal lesion (Kaufman et al., 1996). Intrauterine chemotherapy using OK-432 has also been attempted (Watari et al., 1996). The rationale for these fetal approaches was to prevent polyhydramnios, irreversible facial deformity, and hydrops fetalis.
Cervical Teratoma
Cervical teratomas ( Fig. 15-9 ) are composed of tissues foreign to their normal anatomic sites. All three germ layers are represented within the tumor, whereas neural tissue is the most common histologic component. These tumors are extremely rare; fewer than 200 congenital cases have been described. Prenatal diagnosis of these lesions is usually made on ultrasonography (Bianchi et al., 2000).
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FIGURE 15-9 A fetus undergoing ex-utero intrapartum therapy (EXIT) procedure for cervical teratoma. |
Although cervical teratomas are most often malignant in adults, the vast majority of cervical teratomas in fetuses and infants are benign. The tumor leads to a high incidence of preterm labor and delivery, thought to be secondary to polyhydramnios (a complication in 20% to 40% of prenatally diagnosed cases) or tumor, or both, causing an increase in uterine size. Cesarean section often is recommended because of the abnormal fetal position. Airway obstruction and respiratory compromise can be life threatening after birth. Securing the airway via an EXIT procedure has become a standard procedure for fetal cases with cervical teratoma (Bianchi et al., 2000).
Congenital High Airway Obstruction Syndrome
Congenital high airway obstruction syndrome (CHAOS) is usually caused by laryngeal or tracheal atresia. CHAOS can also be caused by isolated tracheal stenosis or mucosal web or extrinsically by compression from a large cervical mass (e.g., teratoma, lymphangioma). CHAOS can be associated with hydrocephalus, vertebral anomalies, absent radius, bronchotracheal fistula, esophageal atresia, tracheoesophageal fistula, syndactyly, genitourinary anomalies, uterine anomalies, imperforate anus, cardiac anomalies, and anophthalmia. The main differential diagnosis for CHAOS is a bilateral CCAM.
Fetal upper airway obstruction prevents the clearance of lung fluid out of the airway and into the amniotic space. This fluid is normally produced under a pressure that favors its movement out of the fetal mouth. Ultrasonographic findings in CHAOS include large overdistended lungs that compress the mediastinum, bilaterally flattened or everted diaphragms, dilated large airways distal to the obstruction, and fetal ascites and/or hydrops fetalis due to heart and great vessel compression (Hedrick et al., 1994). Fetuses affected with CHAOS are delivered via an EXIT procedure. For fetuses that develop hydrops, early delivery or prenatal tracheostomy is an option, depending on gestational age.
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▪ FETOSCOPIC SURGERY
Fetoscopic surgical procedures are the most common fetal interventions and have the greatest potential to expand in scope of indications. These procedures involve the percutaneous placement of small trocars and fetoscopes into the uterus. Umbilical cord ligation and selective ablation of fetal connecting vessels are done for twin pregnancies complicated by twin reversed arterial perfusion sequence (TRAP) or twin-twin transfusion syndrome (TTTS), where the death of one or both twins is imminent and conventional therapy has failed. Bladder outlet obstruction can be treated using a fetoscope-guided laser to ablate posterior urethral valves, and amniotic bands can be ligated by fetoscopic technique. Also under investigation are fetoscopic techniques to assist in the management of fetuses with congenital diaphragmatic hernias (CDHs).
▪ PREOPERATIVE MANAGEMENT
Because of the emergent nature of these procedures (especially for TTTS and TRAP), parturients may not receive as extensive preoperative evaluation as those undergoing open and EXIT procedures. Patients for fetoscopic surgery are admitted to the hospital on the day of surgery. The operating room is prepared as for an open procedure in the rare event a hysterotomy is required for surgical access. In the preoperative area, the mother receives sodium bicitrate PO, metoclopramide IV, and, if at high risk for preterm labor, indomethacin per rectum. Following placement of American Society of Anesthesiologists standard monitors, a lumbar epidural catheter is inserted and tested. The parturient is then positioned with left uterine displacement to prevent supine hypotension syndrome by compression of the inferior vena cava between the gravid uterus and the spine.
▪ INTRAOPERATIVE MANAGEMENT
Anesthetic management of these cases depends on the location of the placenta, umbilical cord, and amniotic membranes (Galinkin et al., 2000). The location of these structures influences the difficulty of surgical exposure. In the patient with an anterior placenta, epidural anesthesia is often sufficient due to the ease of surgical access to the fetus and essential vessels. A complicating factor is severe polyhydramnios, which can make surgical exposure difficult, requiring general anesthesia to enable uterine manipulation to access the umbilical cord or other fetal structures. In a parturient with a posterior placenta, the uterus is easily accessible but the umbilical cord is often difficult to expose. The presence of a posterior placenta may necessitate a general anesthetic to allow for this additional uterine manipulation. Care should be taken to avoid maternal hyperventilation and hypocapnia, which may result in placental vasoconstriction and fetal hypoxia (Motoyama et al., 1966, 1967; Peng et al., 1972).
The risk for preterm labor increases with hysterotomy for a fetoscopic procedure or a maternal history of preterm labor. Preoperative uterine activity and intraoperative uterine manipulation guide the choice between a balanced general anesthetic, a deep general anesthetic (2 MAC isoflurane or desflurane), and the use of postoperative epidural analgesia. Deep inhalation anesthesia relaxes the uterus, whereas epidural analgesia postoperatively may decrease the risk of preterm labor (Tame et al., 1999). Prophylaxis of preterm labor also includes intraoperative administration of magnesium sulfate. Indomethacin is occasionally used for patients at high risk of preterm labor when cardiac failure is not present in the remaining fetus.
Anesthetic choice is guided by potential advantages and disadvantages for the mother and the fetus ( Table 15-2 ). Epidural anesthesia is used for the majority of these cases and has the advantage of minimal effects on fetal hemodynamics (Hoffman et al., 1997), on uteroplacental blood flow (Alahuhta et al., 1991), and on postoperative uterine activity (Tame et al., 1999). The disadvantages include lack of uterine relaxation, lack of fetal anesthesia, and difficulty manipulating the uterus and cord while the fetus may be moving. A balanced inhalation-opioid anesthetic has the advantage of allowing uterine manipulation with an immobile and anesthetized fetus, yet should provide less fetal cardiovascular depression than deep inhalation anesthesia. General anesthesia also eliminates concerns associated with an awake patient, such as anxiety, combativeness, nausea, and emesis. The potential disadvantage of this technique is an inability to fully relax the uterus to access difficult cord positions. Deep inhalation anesthesia has the advantage of profound uterine relaxation, allowing externalization of the uterus and hysterotomy-based procedures. The disadvantages of this technique are fetal cardiovascular depression and decreased uteroplacental blood flow ( Palahniuk and Shnider, 1974 ; Gaiser et al., 1999) .
TABLE 15-2 -- Implications of anesthetic technique for fetoscopic surgery
|
|
Fetal Depression |
Uteroplacental Blood Flow |
Uterine Relaxation |
|
Regional anesthesia |
— |
— |
— |
|
Balanced general |
|||
|
anesthetic, with/without epidural |
+ |
+/- |
+/- |
|
Deep general anesthetic with epidural |
++ |
++ |
++ |
▪ POSTOPERATIVE MANAGEMENT
As with the open hysterotomy cases, the most important aspect of postoperative management is tocolysis. Epidural catheters are removed after the surgery for these patients, unless they undergo hysterotomy-based procedures. Magnesium sulfate followed by either nifedipine or terbutaline is the mainstay of tocolytic management. Discharge from the hospital on postoperative day 1 to 2 is expected after these procedures.
▪ SURGICAL LESIONS ELIGIBLE FOR FETOSCOPIC SURGERY
Twin Reverse Arterial Perfusion
Twin reverse arterial perfusion (TRAP) occurs only in the setting of a monochorionic pregnancy. This disease process complicates 1% of monochorionic pregnancies and 1:35,000 live births overall ( James, 1977 ). The TRAP sequence is characterized by placental vascular arterioarterial anastomosis between twin fetuses, one being an acardiac/acephalic twin that receives its blood flow from the normal “pumping twin,” thereby endangering the normal twin with high output cardiac failure. Reversal of normal umbilical cord blood flow occurs in the acardiac/acephalic twin, in that blood flows retrograde from the umbilical artery of the normal twin to the acardiac/acephalic twin and returns through the acardiac/acephalic twin's umbilical vein. The “pump” twin supplies the cardiac output for both twins. The acardiac twin is nonviable, and the perinatal mortality rate of the “normal” twin exceeds 50% due to high-output cardiac failure, fetal hydrops, and premature birth ( Moore et al., 1990) .
Management options for the TRAP sequence include observation, termination of the pregnancy, medical treatment of fetal hydrops and preterm labor, or surgical intervention ( Hanafy and Peterson, 1997 ). Surgical cord coagulation by microlaparoscopic technique (fetoscopy) can be performed to interrupt (by laser or bipolar electrocautery) the umbilical artery perfusion to the abnormal twin (Yang andAdzick, 1998 ). The success for this treatment based on multiple case reports in the literature is 67% ( Bianchi et al., 2000) .
Twin-Twin Transfusion Sequence
Twin-twin transfusion sequence (TTTS) also occurs only in monochorionic twins. This syndrome has an incidence of 1 to 9:10,000 births ( Bianchi et al., 2000) . This disease results from an imbalance of blood flow across vascular anastomoses between the two fetal circulations. These twins are discordant in size, with oligohydramnios in the donor twin and polyhydramnios in the recipient twin ( Fesslova et al., 1998) . If fetal death occurs in the recipient, the co-twin is at very high risk of death (as high as 50%) or neurologic injury ( van Heteren et al., 1998 ; Ries et al., 1999) .
The severity of TTTS dictates the choice of surgical management technique. Selective fetoscopic laser photocoagulation (SFLP) of the twin-twin vascular anastomoses is performed when both twins can be saved. SFLP is used to selectively ablate vessels lying on the surface of the placenta that abnormally connect the vasculature of the twins. Umbilical cord coagulation is performed for twin gestations with end-stage TTTS, where one fetus is nonviable and threatens the life or neurologic state of the viable twin. This process separates the fetal circulations and protects the donor twin when the recipient twin is premorbid and not a candidate for SFLP.
Amniotic Bands
The amniotic band syndrome (ABS) consists of a group of congenital anomalies caused by constrictive bands that develop in the amniotic fluid. Deformities occur in the limbs, craniofacial regions, and trunk and appear as pseudosyndactyly, amputation, and/or craniofacial, visceral, or body wall defects. The incidence of these lesions is 1:1,200 to 1:15,000 live births ( Chemke et al., 1973 ; Ho and Liu, 1987 ; Ray et al., 1988) . It is believed that amniotic bands are caused by early rupture of the amnion, resulting in mesodermic bands that originate from the chorionic side of the amnion and insert on the fetal body. These bands have been replicated in an experimental model ( Crombleholme et al., 1995) and can lead to amputations, constrictions, and postural deformities secondary to immobilization.
Fetoscopic surgery for the release of amniotic bands is a limb- and life-saving technique. The earlier the band occurs, the more severe is the resulting lesion. Amniotic rupture in the first weeks of pregnancy may result in craniofacial and visceral defects, whereas during the second trimester, the fetal morbidity ranges from formation of syndactyly to limb amputation. Threatened limb amputation may have devastating morphologic and functional effects on a limb, but it is not lethal. These patients are closely followed by repeated ultrasonographic evaluation. When limb compromise becomes an issue, fetoscopic surgery is performed to release these constricting bands. Umbilical cord constriction by amniotic bands can also occur with lethal consequences ( Graf et al., 1997 ; Strauss et al., 2000) and is an emergent indication for fetal surgery. For this disease process, fetoscopic intervention can dramatically improve fetal outcome.
Congenital Diaphragmatic Hernia
Congenital diaphragmatic hernia (CDH) is a simple defect in the diaphragm in which abdominal viscera herniate into the chest, most often through a posterolateral defect in the diaphragm. It is thought to be due to failure of the pleuroperitoneal canal to close between 9 to 10 weeks of gestation. This lesion can result in pulmonary hypoplasia and pulmonary hypertension from compression of the developing lungs by the herniated viscera ( Harrison et al., 1993) . Despite advances in prenatal care, maternal transport, neonatal resuscitation, and the availability of extracorporeal membrane oxygenation, the physiologic consequences of the disease are associated with a high neonatal mortality rate and substantial long-term morbidity ( Harrison et al., 1978) .
The prenatal diagnosis of CDH is made on ultrasonographic demonstration of abdominal content such as bowel, stomach, or liver in the thorax. Because fetal pulmonary function cannot be assessed in utero, several sonographically detectable predictors of the severity of a CDH have been proposed. The two most important parameters are the lung-to-head ratio (LHR) ( Lipshutz et al., 1997) and the position of the left lobe of the liver ( Albanese et al., 1998) . The LHR is the calculated volume of the contralateral lung (the ipsilateral lung cannot be identified with a CDH) indexed to head circumference to adjust for gestational age. Fetuses with an LHR of more than 1.4 have a relatively good prognosis with postnatal care and are not candidates for fetal intervention. Fetuses with a major portion of the left lobe of the liver herniated into the hemithorax have an approximately 50% survival rate, whereas those with the liver in normal abdominal position have a greater than 90% survival rate ( Albanese et al., 1998) .
The prenatal treatment strategy for CDH has undergone continuous development since the first attempted CDH repair in 1986 (Harrison et al., 1990, 1993 [43] [44]). Open fetal surgery was associated with many technical problems. Data from a National Institutes of Health-funded prospective study demonstrated that repair of the diaphragm for those without liver herniation was no better than standard postnatal care ( Harrison et al., 1997) . Repair in cases with liver herniation was not technically feasible.
Knowledge from study of fetuses with CHAOS that resulted in hyperplastic lungs due to overdistention by lung fluid led to a new concept of CDH treatment ( Hedrick et al., 1994) . Midgestation tracheal occlusion was evaluated in human fetuses with severe CDH in an attempt to promote lung expansion. For this procedure, fetoscopically placed titanium clips were applied to temporarily occlude the fetal trachea ( Bealer et al., 1995 ; Harrison et al., 1996, 1998 [46] [47]; Skarsgard et al., 1996 ; VanderWall et al., 1996) . The tracheal clips were removed in an EXIT procedure ( Mychaliska et al., 1997) . This technique was successful in increasing lung size but was abandoned due to poor fetal outcomes. A technique using a fetoscopically placed detachable tracheal balloon, which is removed at birth, was then developed, replacing the technique of tracheal clips through the anterior tracheal dissection of the fetus ( Harrison et al., 2001) .
A National Institutes of Health-sponsored randomized controlled trial of the detachable balloon technique was conducted between April 1999 and July 2001. The trial involved 24 pregnant women with a single fetus between 22 and 27 weeks of gestation and with left-sided CDH, liver herniation into the left hemithorax, and an LHR of less than 1.4 ( Harrison et al., 2003) . Under deep halothane anesthesia with nitroglycerin as needed, a 4-mm hysteroscope was passed through a 5-mm trocar and guided through the fetal vocal cords. The balloon was placed in the fetal trachea and inflated with isotonic contrast material. All 11 fetuses in the tracheal occlusion group were delivered by the EXIT procedure. Eight of 11 fetuses (73%) in the intervention group and 10 of 13 (77%) in the control group (neonatal surgery) survived more than 90 days. The rate of neonatal morbidity did not differ between the two groups, but premature rupture of the membrane and preterm delivery were significantly more common in the tracheal occlusion group (31 versus 37 weeks) ( Harrison et al., 2003) . Based on these results, fetal surgery for CDH was suspended in the United States in April 2001 with an indefinite moratorium.
Hydronephrosis—Bladder Outlet Obstruction
Obstructive uropathy occurs in 1:1,000 live births ( Estes and Harrison, 1993 ). Unlike obstruction of the urinary tract at other levels, bladder outlet obstruction has the potential to affect the development of the whole urinary tract and the pulmonary system. Bladder outlet obstruction can lead to oligohydramnios and result in renal failure from renal dysplasia. Secondary pulmonary hypoplasia may also develop, leading to severe respiratory insufficiency at birth. Fetuses with obstructive uropathy can also have other associated nongenitourinary anomalies, chromosomal anomalies, and deformations related to oligohydramnios.
Prenatal intervention is possible for select fetuses with urinary tract obstruction. In cases of isolated bladder outlet obstruction due to posterior urethral valves, fetal vesicoamniotic shunting may be life saving. Fetuses are selected for this intervention based on three variables: fetal karyotype, detailed sonographic evaluation, and serial urine evaluation to determine the extent of underlying renal damage (Evans et al., 1991 ; Walsh and Johnson, 1999 ). The aim of prenatal intervention is to bypass or directly treat the obstruction, restoring amniotic fluid to normal levels.
Initially, open fetal surgery to place a vesicoamniotic shunt was performed for fetuses with severe bladder outlet obstruction. Unfortunately, this technique was abandoned due to the high complication rate for both mother and fetus ( Crombleholme et al., 1988) . Vesicoamniotic shunts have also been placed percutaneously under sonographic guidance, but catheter placement is not always successful and catheter displacement and obstruction occur in 25% of the cases. Fetoscopic ablation of posterior urethral valves is a technique developed in a fetal-lamb model that is now being used in humans ( Quintero et al., 1995) . This technique holds a great deal of promise for improving the treatment of urinary tract obstruction in utero ( Estes et al., 1992) . The technique involves in utero percutaneous cystoscopy followed by ablation of the posterior urethral valves by laser ( Quintero et al., 1995) . The use of this minimally invasive technique may greatly reduce the morbidity of in utero treatment of serious bladder outlet obstruction compared with standard therapy.
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Copyright © 2005 Mosby, An Imprint of Elsevier
▪ CONTROVERSIES
Fetal surgery is a new frontier of medicine. As with other emerging fields, such as stem cell research and gene therapy, controversy surrounds many aspects of these procedures. Anesthetic aspects are no exception. An editorial from Anesthesiology ( Anand and Maze, 2001 ) questioned whether fetuses are appropriately anesthetized during fetal interventions. Based on animal and human literature, the fetus receives at least half the MAC concentration of anesthetic agent received by the mother ( Palahniuk et al., 1974 ; Schwarz et al., 2003 ), and fentanyl administered intramuscularly to the fetus sufficiently blocks the fetal stress response ( Fisk et al., 2001) . Similarly, the lack of movement noted in the fetus during these procedures indicates adequate anesthesia. It is not known whether eliciting a stress response in a fetus causes any long-term effects or if the lack of long-term analgesia after fetal surgery is detrimental to outcome.
The use of volatile anesthetics as sole anesthetics for fetal surgery is a technique that has evolved over time and remains controversial. The traditional anesthetic technique for fetal surgery was a nitrous oxide-opioid technique that used intravenous nitroglycerin to provide uterine relaxation. This technique causes a labile maternal blood pressure and inconsistent uterine relaxation. The technique of deep general anesthesia evolved in response to these problems. Deep general anesthesia provides the benefit of profound uterine relaxation and predictable maternal decreases in blood pressure that are readily responsive to intravenous ephedrine. Traditionally, isoflurane and halothane were the inhalation agents of choice for this technique. Now, with the advent of more insoluble inhalation agents, desflurane is the primary agent used at many institutions for these cases due to ease of titratability. Unfortunately, there are little clinical or animal data showing superiority or maternal/fetal safety for any of these techniques.
Future research in fetal anesthesia is fraught with difficulty. Standardized assessment tools and blood “microsampling” techniques for the fetus need to be developed to allow further development of clinical protocols. Questions regarding fetal stress and optimal drug dosing in the fetus remain open to speculation until these techniques evolve to answer our questions.
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Motoyama & Davis: Smith's Anesthesia for Infants and Children, 7th ed.
Copyright © 2005 Mosby, An Imprint of Elsevier
▪ SUMMARY
Anesthesia for fetal surgery continues to evolve. The anesthetic techniques that have emerged are safe for mother and fetus. Because of the myriad anesthetic and surgical issues that these cases generate, it is essential to have good communication and cooperation between surgeons, anesthesiologists, and perinatal physicians. This communication must exist from the preoperative period to the postoperative period to allow development of a cohesive anesthetic and surgical plan that can be used for the safe perioperative management of the fetal surgery patient.
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Motoyama & Davis: Smith's Anesthesia for Infants and Children, 7th ed.
Copyright © 2005 Mosby, An Imprint of Elsevier
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