11
Anesthesia
Theodore J. Sanford Jr, MD
Anesthesiology is a “team sport.” Providing the best and safest care for patients depends on all members of the team—surgeons, nurses, and anesthesia providers—communicating in a timely, efficient, and patient-focused manner. Anesthesiologists today not only provide patient care in the operating room but also have patient responsibilities in other areas, including preoperative anesthesia clinics (PACs), postanesthesia care units (PACUs), obstetrics, ambulatory surgery centers, endoscopy suites, postoperative pain management, critical care units, and chronic pain management.
Anesthesia is a term derived from the Greek meaning “without sensation” and is commonly used to indicate the condition that allows patients to undergo a variety of surgical or nonsurgical procedures without the pain or distress they would otherwise experience. More importantly, this blocking of pain and/or awareness is reversible. Anesthesiology is the medical practice of providing anesthesia to patients and is most commonly provided by a medical doctor, an anesthesiologist, either alone or in conjunction with a certified registered nurse anesthetist (CRNA), anesthesia assistant, or resident physician-in-training. Anesthesia is most often described as being a general anesthetic, that is, a drug-induced loss of consciousness during which patients are not arousable even by noxious stimulus and often require a controlled airway. Anesthesia can also be provided without inducing unconsciousness by utilizing regional blockade, local anesthesia with monitored anesthesia care (MAC), or conscious sedation.
HISTORY OF ANESTHESIA
One of modern medicine’s most important discoveries was that the application of diethyl ether (ether) could provide the classic requirements of anesthesia: analgesia, amnesia, and muscle relaxation in a reversible and safe manner. Crawford Long was the first to use ether in 1842, and William Morton’s successful 1846 public demonstration of ether as an anesthetic in the “Ether Dome” of Massachusetts General Hospital ushered in the modern day of anesthesia and surgery. Chloroform was used by Sir James Y. Simpson to provide analgesia to Queen Victoria in 1853 during the birth of Prince Leopold. This royal approval of inhalation agents led to the wide acceptance of their use as surgical anesthesia. Ether (flammability, solubility) and chloroform (liver toxicity) each had significant drawbacks, and over time, inhalation agents were developed with similar anesthetic effects but much safer physiologic and metabolic properties.
Cocaine’s ability to produce topical anesthesia for ophthalmic surgery was discovered in the late 1800s. The hypodermic needle was introduced in 1890 and facilitated the injection of cocaine to produce reversible nerve blockade and later the injection of cocaine via a lumbar puncture to produce a spinal anesthetic and the first spinal headache. The chemical properties of cocaine were soon determined and manipulated to synthesize numerous other local anesthetic agents used to achieve what became known as regional anesthesia, which lacks the unconsciousness and amnesia of the general anesthetics but does produce analgesia and lack of motor movement in the “blocked” region.
Underwood EA: Before and after Morton. A historical survey of anaesthesia. Br Med J. 1946;2:525.
OVERALL RISK OF ANESTHESIA
Anesthesia is performed over 70 million times per year in the United States and is remarkably safe. The number of anesthesia-related deaths has decreased dramatically in the last 30 years because of intense scrutiny by the American Society of Anesthesiologists. The realization that most problems are related to airway compromise has led to advanced respiratory monitoring utilizing pulse oximetry and capnography for every patient undergoing anesthesia. The Institute of Medicine’s To Err Is Human complimented the anesthesiology community for its marked decrease in morbidity and mortality from anesthesia. Overall, the risk of anesthesia-related death in the healthy patient is estimated to be as low as 1:100,000-200,000 anesthetics.
The combination of amnesia, with or without unconsciousness, analgesia, and muscle relaxation is purposely induced by an anesthetic caregiver and is achieved either by administering inhalation agents in appropriate doses to affect the central nervous system (CNS) or by using specific intravenous pharmacologic agents to produce the same effects as inhaled vapors. These agents include amnestics, for example, benzodiazepines (midazolam or diazepam); analgesics, for example, the opioids morphine and fentanyl derivatives; the neuromuscular blocking drugs succinylcholine, pancuronium, or vecuronium; and sedative hypnotics, for example, sodium pentothal and propofol. All of the agents have adverse physiologic consequences: respiratory depression, cardiovascular depression, and loss of consciousness. Furthermore, some of these agents may induce allergic reactions. Some have also been known to trigger malignant hyperpyrexia.
The most common problems associated with adverse outcomes today still relate to airway compromise, medication errors, and central venous cannulation. Other concerns are postoperative neurologic complications (eg, nerve injury), ischemic optic neuropathy, coronary ischemia, anesthesia in remote locations (eg, interventional radiology sites), and probably most importantly, inadequate preoperative evaluation and preparation.
The anesthesia provider must be able to (1) achieve a state of anesthesia quickly and safely by choosing the appropriate techniques and agents, taking into consideration the patient’s medical condition; (2) maintain and monitor a state of anesthesia throughout the surgical procedure while compensating for the effects of varying degrees of surgical stimulation and blood and fluid losses; (3) reverse the muscle relaxation and amnesia as necessary; and (4) return the patient to physiologic homeostasis while maintaining sufficient analgesia to minimize postprocedure pain.
Kohn LT, Corrigan JM, Donaldson MS (editors): To Err Is Human: Building a Safer Health System. Washington, DC: National Academy Press, 2000.
PREOPERATIVE EVALUATION
A preoperative evaluation is a responsibility of the anesthesiologist and is a basic element of anesthesia care (Table 11–1). This evaluation consists of information gathered from multiple sources, including the patient’s medical record, history and physical examinations, and findings from medical tests and consults or other evaluations performed prior to the patient being seen by the anesthesiologist. Improved patient outcome and satisfaction is the result of an adequate, structured, formal presurgical, or preprocedure evaluation and preparation performed on all patients.
Table 11–1. Preoperative evaluation.
|
Goals Optimize patient condition Understand and control comorbidities and drug therapy Ensure patient’s questions are answered Timing High surgical invasiveness: at least 1 day prior Medium invasiveness: day before or day of surgery Low invasiveness: day of surgery Content Review medical records Directed history and physical examination: airway, heart, and lungs Indicated laboratory or additional consultations |
Timing
The timing of the preoperative evaluation depends primarily on the degree of planned surgical invasiveness. For high surgical invasiveness, the initial assessment should be done at a minimum the day before the planned procedure by the anesthesia staff. Patients undergoing medium surgical invasive procedures can be evaluated the day before or even on the day of surgery, and for low surgical invasiveness, the initial assessment may be done the day of surgery. Time must be allotted to follow up on conditions discovered during the preoperative visit and to answer patient questions. Perioperative complications and deaths are most often a combination of patient comorbidities, surgical complexity, and anesthesia effects. The Physical Status Classification of the American Society of Anesthesiologists is the best known of many perioperative classification schemes (Table 11–2). This classification system does not assign risk but is a common language used to describe patients’ preoperative physical status. The system is an alert to the anesthesia practitioner and all members of the patient care team.
Table 11–2. American Society of Anesthesiologists physical status classification.
|
ASA 1 (PS1): A normal healthy patient ASA 2 (PS2): A patient with mild systemic disease ASA 3 (PS3): A patient with severe systemic disease ASA 4 (PS4): A patient with severe systemic disease that is a constant threat to life ASA 5 (PS5): A moribund patient who is not expected to survive without the operation ASA 6 (PS6): A declared brain-dead patient whose organs are being removed for donor purposes E: Emergency |
Patients should ideally be seen in a PAC staffed by anesthesia personnel who evaluate patients from the anesthetic perspective and who look for physical conditions (airway) and controlled, uncontrolled, or unrecognized medical conditions that can lead to perioperative morbidity and mortality. There must be adequate communication between anesthesiologist and surgeon such that any conditions that may result in patient compromise are optimally addressed. Optimally, a patient’s medical status has been adequately addressed by the patient’s primary care physician prior to being referred to the PAC. However, in some instances, only a cursory “cleared for anesthesia and surgery” may result in a necessary delay. Any patients other than healthy ASA 1 or 2 patients should be seen in a PAC. Prior to referring patients to the PAC, the surgeon should have already ordered the necessary preoperative labs and in many instances will have already detected uncontrolled medical conditions that require consultations from other specialties in order to recommend and in some instances improve a patient’s status.
The optimal preoperative evaluation has the following two elements: (1) content—readily accessible medical records, patient interview, a directed preanesthesia examination, indicated preoperative laboratory tests, and additional consultations when indicated; the minimum acceptable examination includes an assessment of the airway, heart, and lungs well in advance of the planned date of surgery; and (2) preoperative tests—only as indicated by comorbidities and never as a screen, these tests should be specifically aimed at helping the anesthesiologist formulate an anesthetic plan.
Practice advisory for preanesthesia evaluation: a report by the American Society of Anesthesiologists Task Force on Preanesthesia Evaluation. Anesthesiology. 2012;116:1-17.
History & Physical Examination
The anesthesiologist should specifically ask the patient about previous operations, anesthetic type, and any complications, for example, allergic reactions, abnormal bleeding, delayed emergence, prolonged paralysis, difficult airway management, awareness, or jaundice. Each of these describes a possible specific anesthetic morbidity that must be further investigated either by history or specific testing. Medical conditions detected as decreased exercise tolerance, shortness of breath, orthopnea, kidney or liver disease, and metabolic abnormalities, for example, diabetes or thyroid disease, should be ascertained. A comprehensive history seeks to identify serious cardiac conditions, for example, unstable coronary syndromes, angina, myocardial infarctions either recent or past, decompensated congestive heart failure, significant arrhythmias, or severe valvular disease. Any recent changes in cardiac symptoms or other associated diseases, for example, diabetes, renal disease, or cerebrovascular disease symptoms, should be identified.
Any family history of adverse responses to anesthetics (malignant hyperthermia) and social history of smoking, drug use, and alcohol consumption is important. Finally, a comprehensive review of concurrent medications including antihypertensives, insulin, bronchodilators, or any other medications that can interact with anesthetic agents should be documented. Certain medications may result in increased or decreased anesthetic requirements, prolongation of muscle relaxants, abnormal responses to sympathomimetics, delayed or enhanced metabolism of anesthetics, and/or augmentation of the depressant effects of anesthetics. The patient’s use of herbal medicines can have an adverse reaction with some anesthetics (Table 11–3) and all should be discontinued 2-3 weeks before surgery.
Table 11–3. Perioperative effects of common herbal medicine.1
Wong A, Townley SA: Herbal medicines and anaesthesia. Br J Anaesth. 2011;11:15-17.
Airway Examination & Classification
After the vital signs are obtained, the physical examination begins with the upper airway. Ability to control the airway is mandatory. The focus of the examination is to assess those factors that would make airway control (eg, endotracheal intubation) difficult or impossible. Seven keys to the upper airway examination should be documented:
Figure 11–1. Mallampati airway classification of oral opening. (Reproduced with permission from Morgan GE, Mikhail MS, Murray MJ: Clinical Anesthesiology, 4th ed. McGraw-Hill.)
Grade I The soft palate, anterior and posterior tonsillar pillars, and uvula are visible—suggests easy airway intubation.
Grade II Tonsillar pillars and part of the uvula obscured by the tongue.
Grade III Only soft palate and hard palate visible.
Grade IV Only the hard palate is visible—suggests challenging airway.
The physical examination then focuses on heart and lungs, potential intravenous catheter sites, and potential sites for regional anesthesia. Range of motion of limbs must also be noted as this may affect positioning in the operating room. Finally, any neurologic abnormalities must be noted.
When a metabolic or physical finding or symptom is discovered during this visit, the anesthesiologist may believe that a specialty consultation is necessary to suggest ways to optimize the patient for surgery and anesthesia. If this is the case, the anesthesiologist should communicate with the surgeon in order to prevent unnecessary or unexpected delays in the surgical schedule. It is imperative that any consults ordered be completed and the results be available by the day of surgery.
The anesthesiologist can then advise the patient on appropriate options for general anesthesia versus regional techniques based on the patient’s history, physical examination, and type of surgery. Although some surgical procedures must always be performed under general anesthesia, the anesthesiologist may discuss other options with the patient. If the referring surgeon has a particular preference for a type of anesthetic, such preferences should be communicated to the anesthesiologist directly rather than through the patient. It is also best if the referring surgeon does not promise any specific agent or technique without first consulting with the anesthesia care givers.
Mallampati SR et al: A clinical sign to predict difficult tracheal intubation: a prospective study. Can Anaesth Soc J. 1985;32:429.
Preoperative Fasting
The anesthesiologist must discuss with the patient the requirements for preprocedure fasting and the management of medications up to the time of surgery or procedure. Current guidelines for preoperative fasting are as follows: (1) No solid food should be eaten after the evening meal. At the minimum, most anesthesiologists delay an anesthetic so that the last solid food was 6-8 hours prior to nonemergent surgery or procedures involving anesthesia. (2) NPO after midnight except for sips of water to take oral medications. Water may be ingested up to 2 hours before checking in for surgery. Some institutions allow other clear liquids, for example, coffee, a few hours prior to surgery or procedure. However, because surgery schedules can change abruptly and procedure time may be moved forward, NPO after midnight is the best policy. (3) Pediatric fasting guidelines vary among institutions, so practitioners should consult with their particular pediatric anesthesia group.
American Society of Anesthesiologists: Practice guidelines for preoperative fasting and the use of pharmacologic agents to reduce the risk of pulmonary aspiration: application to healthy patients undergoing elective procedures. Anesthesiology. 2011;114:495-511.
Drugs to Continue Preoperatively
In the perioperative period patients should continue taking beta-blocking agents, statin medications, antihypertensives except the angiotensin II receptor blockers (ARBs) and angiotensin-converting enzyme inhibitors (ACE) antihypertensive medications. Patients taking ARBs or ACE inhibitors can experience marked hypotension with the induction of general anesthesia and respond poorly to common vasopressors. Patients taking anticoagulants such as Coumadin, clopidogrel, and the newer anticoagulants such as dabigatran (Pradaxa) should stop these medications prior to most surgeries. The timing and bridging of cessation of these anticoagulants is the responsibility of the surgical service. Continuation of low-dose aspirin for patients with coronary stents or atrial fibrillation is recommended. Oral antihyperglycemic agents need should not be taken the day of surgery. Insulin-dependent patients should receive instructions from the anesthesiologist during the preanesthesia visit as to the management of their insulin. Other medications should be discussed with the patient and surgery team at the time of the preoperative anesthesia visit.
Comorbidities
Comorbidities should be well controlled in the preoperative period to avoid postprocedure morbidity, and even mortality.
Cardiovascular Disease (Hypertension, Coronary Artery Disease, Congestive Heart Failure)
Hypertension is the most common preexisting medical disease identified preoperatively and is a major risk factor for renal, cerebrovascular, peripheral vascular, cardiac ischemia or infarction, and congestive heart failure. The triad of lipid disorders, diabetes, and obesity is classically found in patients with hypertension and should alert the clinician that further evaluation for these conditions is needed. Hypertension has an association with coronary artery disease, and the preoperative evaluation is a unique opportunity to identify and treat the nonessential causes of hypertension. The literature strongly supports the notion that all hypertensive patients should be treated medically to be as close to normotension as possible before any planned surgical procedure. Diastolic pressures of 110 mm Hg or higher result in a higher incidence of intraoperative hypotension and myocardial ischemia. However, the literature does not support delaying surgery if the delay would be detrimental to the patient. The introduction of perioperative selective beta-blocking drugs provides a marked benefit in reducing the incidence of significant myocardial ischemia during the perioperative period. Although somewhat controversial, starting patients on beta-blockers immediately preoperatively may have some risk, but any patient already taking beta-blockers should continue taking the drug preoperatively.
Sear JW, Giles JW, Howard G, Foex P: Perioperative beta-blockade, 2008: what does POISE tell us, and was our earlier caution justified? Br J Anaesth. 2008;101:135-138.
Wax DB et al: Association of preanesthesia hypertension with adverse outcomes. J Cardiothorac Vasc Anesth. 2010:24(6): 927-930.
Ischemic heart disease is a leading cause of death in the United States and is the leading cause of morbidity and mortality in the perioperative period. About 25% of patients who present for surgery each year have coronary artery disease, and thus much of the preoperative evaluation focuses on detecting the presence and degree of ischemic heart disease and determining whether it is likely to impact anesthesia and surgery. A major goal of preoperative assessment of cardiac status is to determine what, if any, interventions—coronary artery bypass graft (CABG), percutaneous coronary intervention (PCI)—would benefit patients undergoing noncardiac surgery. In general, preoperative cardiac tests are recommended only if the information obtained will lead to changes in patient management. However, certain active clinical conditions (Table 11–4) demand evaluation and treatment before noncardiac surgery. Determining which patient characteristics indicate high perioperative risk is very difficult, but the Revised Cardiac Risk Index (RCRI) factors of (1) ischemic heart disease, (2) heart failure, (3) high-risk surgery, (4) diabetes mellitus, (5) renal insufficiency, and (6) cerebral vascular diseases are a validated set of independent predictors of cardiac risk for patients. The anesthesiologist in a pre-op clinic will screen for these factors and recommend further studies based on the presence or absence of RCRIs. Patients with no RCRIs have a very low (0.4%) cardiac risk while patients with three or more risk factors have a 5.4% risk of an adverse cardiac event and warrant further testing. Because of the high incidence of silent ischemia, some institutions will require patients older than 50 to have an electrocardiogram (EKG). A simple exercise tolerance description of the functional capacity of the patient (eg, ability to climb two flights of stairs without stopping) is also a practical screening. This initial history by the surgeon or anesthesiologist may be the first cardiac assessment the patient has ever had. The assessment of functional capacity may be the first indication of the need for further evaluation of potential cardiac pathology.
Table 11–4. Active cardiac conditions for which the patient should undergo evaluation and treatment before noncardiac surgery.
The American Heart Association (AHA) developed a useful algorithm for all providers (Figure 11–2). This algorithm, updated in 2007, no longer focuses on stress testing but recommends testing only if the results could have an impact on surgery or anesthesia and lead to changes in patient management. The AHA guidelines state that most patients who have asymptomatic heart disease can safely undergo elective noncardiac surgery without performing invasive or even noninvasive cardiac testing.
Figure 11–2. Cardiac evaluation and care algorithm for noncardiac surgery based on active clinical conditions, known cardiovascular disease or cardiac risk factors for patients 50 years of age or greater. Summary of ACC/AHA 2007 perioperative guideline algorithm on cardiovascular evaluation and care for noncardiac surgery. HR = heart rate, LOE = loss of evidence, MET = metabolic equivalent.
Fleisher LA et al: 2009 ACCF/AHA Focused Update on Perioperative Beta Blockade Incorporated Into the ACC/AHA 2007 Guidelines on Perioperative Cardiovascular Evaluation and Care for Noncardiac Surgery A Report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Circulation. 2009;120: e169-e276.
Ford MK et al: Systematic review: prediction of perioperative cardiac complications and mortality by the revised cardiac risk index. Ann Intern Med. 2010:152:26.
There is much controversy about the best treatment for patients who have had a PCI procedure, angioplasty without stents, or angioplasty with either a bare metal or drug-eluting stent. Because of the risk for thrombosis at the site of intervention, patients are usually placed on a dual antiplatelet therapy of aspirin and clopidogrel for 2-4 weeks following angioplasty, 4-6 weeks for the bare metal stents, and up to 1 year for the drug-eluting stents. Stopping these antiplatelet drugs for a surgical intervention that falls in the therapy period presents a risk for perioperative cardiac events if the stent thromboses. The AHA guidelines recommend that if the procedure is elective, then the operation should be postponed until the case can be done with aspirin as the only antiplatelet drug. If the operation is urgent, then consideration must be given to the timing of the surgery and the risk of surgical bleeding. If the risk of bleeding is low, then a PCI with a stent should be considered and the patient placed on dual antiplatelet therapy. If the bleeding risk is high, the AHA recommends the following based on the timing of surgery: angioplasty for surgery within 14-29 days, bare metal stent for planned surgery within 30-365 days, and drug-eluting stent for surgery that can be delayed 1 year. Truly urgent and/or emergent surgery necessitates angioplasty for a procedure with a high risk of surgical bleeding and stenting for a case with a low risk for bleeding.
The AHA guidelines recommend several other measures: (1) Perioperative beta-blockade is indicated for patients previously on beta-blockers, patients undergoing major vascular surgery, and patients undergoing intermediate-risk surgery with one or more RCRIs. Beta-blockade may be started several days to weeks before planned surgery in order to produce a consistent targeted heart rate between 65 and 70 beats/min. The addition of statin class agents, alpha-2 agonists, and calcium channel blockers may also be effective. (2) Left ventricular function should be assessed preoperatively for patients with unexplained dyspnea or who have active or a history of compensated heart failure with changing symptoms. (3) Coronary revascularization is suggested for patients with left main disease, symptomatic three-vessel disease and poor ejection fraction (EF), two-vessel disease with left anterior descending coronary artery stenosis, poor EF and a positive stress test, or an acute ST segment elevation myocardial infarction. AHA does not recommend prophylactic CABG surgery in patients with stable coronary artery disease. (4) Blood glucose should be tightly controlled. (5) Patients with pacemakers or implanted defibrillator devices should have them checked 3-6 months before major surgery. (6) Patients with drug-eluting cardiac stents should continue aspirin therapy and discontinue other antiplatelet agents for as short a time as possible. (7) Beta-blockers and statin drugs should be continued in the perioperative period. (8) Cardiology consultants should be asked for specific recommendations that would reduce immediate perioperative cardiac risk.
Practice alert for perioperative management of patients with coronary artery stents. Anesthesiology. 2009:110:1-2.
The presence of significant pulmonary disease is suspected or confirmed by the history and physical examination. Poor functional capacity may be the first indication that further workup may be necessary. The presence of either obstructive or restrictive lung disease always puts the patient at risk for perioperative complications, for example, pneumonia and prolonged difficulty weaning from the ventilator. In some instances, arterial blood gas analysis or pulmonary function tests are necessary to determine responsiveness to bronchodilators. Asthmatic patients should be asked about the severity of their disease, hospitalizations, responsiveness to inhalers, and steroid usage. There is no value for routine preoperative chest x-rays. Surgical history and physical examination may be the first indication of significant pulmonary disease, and workup may be initiated before sending the patient to the PAC. Optimally, patients who smoke should stop smoking at least 8 weeks before scheduled surgery. Warner demonstrated that the highest rate of pulmonary complications in 200 patients undergoing CABG was in those who had stopped smoking 1-8 weeks preoperatively. Recent cessation of cigarette smoking may pose a greater risk of pulmonary complication because of the commonly observed increase in cough and sputum production. Patients should abstain from smoking for as long as possible both before and after surgery.
Warner DO: Helping surgical patients quit smoking: why, when, and how. Anesth Analg. 2005;101:481.
The national epidemic of obesity poses particular problems for surgery and anesthesia. The body mass index (BMI), the ratio of weight (kg)/height (m2), gives an idea of the degree of obesity. Normal BMI is about 21.6 kg/m2, overweight is 25-30 kg/m2, obese is 30-35 kg/m2, and extreme obesity is more than 35 kg/m2. Extreme obesity patients have a variety of perioperative issues and should be evaluated in a PAC. Particular attention should include the upper airway and evaluation of cardiovascular, respiratory, metabolic, and gastrointestinal systems. Abnormal BMI patients have cardiovascular issues with venous access, hypertension, cardiomegaly, decreased left ventricular function, and cor pulmonale, and they have twice the incidence of ischemic heart disease than patients at normal weight. Extreme obesity is associated with significant pulmonary problems, including restrictive lung volumes, obstructive sleep apnea, hypoxemia, increased Paco2, increased hematocrit, and right heart failure. The extremely obese patient’s airway is often difficult to maintain with mask ventilation secondary to decreased neck mobility and adiposity and requires careful preoperative evaluation. Almost all the major endocrine problems with extreme obesity involve the effects of diabetes mellitus and require preoperative assessment of glycemic control. Obesity also leads to abnormal fatty deposits in the liver that cause increased metabolism of inhalation anesthetics. Morbidly obese patients may have a higher risk of gastric aspiration and development of aspiration pneumonia. Finally, postoperative pain management must be considered.
The most common metabolic abnormality is diabetes mellitus, and its presence should cause a high index of suspicion for cardiac problems. Patients on insulin therapy are at higher risk for cardiac morbidity and mortality, including myocardial infarction and heart failure. Glucose control may be very difficult to maintain in the perioperative period, and preoperative assessment of control should always be ascertained through history or laboratory testing. Tight glucose control may reduce infections postoperatively but it is controversial whether intensive insulin therapy decrease mortality, perioperative hypoglycemia, or cardiac events. Anesthesia providers are responsible for glucose control during the procedure, and the surgical service is typically responsible for this care in the postoperative period.
Hua J et al: Intensive intraoperative insulin therapy versus conventional insulin therapy during cardiac surgery: a meta-analysis. J Cardiothoracic Vasc Anesth. 2012;26(5):829-834. Epub Feb 14, 2012.
Patients taking low-molecular-weight heparin (LMWH) for deep venous thrombosis prophylaxis present an unusual problem for both surgeon and anesthesiologist. The current guidelines dictate that unless absolutely indicated, neuraxial anesthesia (spinal, epidural) should not be performed unless LMWH has been stopped for at least 12 hours and preferably 24 hours. That means that a substitute anticoagulant should be initiated if neuraxial anesthesia is to be done, or this approach is avoided.
Acute renal failure (ARF) occurs in approximately 1%-5% of all hospitalized patients and is responsible for increased length of stay and mortality. The preoperative visit can help to identify patient risk factors for ARF in those with previously normal renal function undergoing noncardiac surgery. The perioperative onset of ARF in patients with previously normal renal function is associated with increased postoperative mortality, especially significant within 1 year postsurgery. BMI higher than 32 kg/m2, age, emergency surgery, liver disease, high-risk surgery (intrathoracic, intraperitoneal, suprainguinal vascular, large blood loss), peripheral vascular occlusive disease, and chronic obstructive pulmonary disease necessitating chronic bronchodilator therapy place patients at increased risk for perioperative renal impairment.
Kheterpal S et al: Predictors of postoperative acute renal failure after noncardiac surgery in patients with previously normal renal function. Anesthesiology. 2007;107:892.
Preoperative Medications
The use of preoperative medications is hampered by the fact that most patients are not in the medical facility until the day of surgery. Most premedications now consist of an anxiolytic agent (eg, midazolam) and an opiate (eg, fentanyl) given in the immediate preanesthesia period. These premedications are often given because patients have a preconceived notion that they need something to relax. Alternatively, a thorough explanation of what the patient can expect in terms of surgery and anesthesia has a significant calming effect comparable to that of medications given to relieve anxiety. Administration of premedication to prevent pulmonary aspiration syndrome is often considered with the use of agents that increase gastric pH (H2 blockers, proton pump inhibitors, antacids) or agents that lower gastric volume.
Informed Consent
Many institutions and practices obtain a signed informed consent from patients for anesthesia, while other institutions include the anesthesia consent in the surgical consent. Regardless of the particular facility requirements, the anesthesiologist should write a note in the patient chart indicating that the patient has been informed of the issues surrounding anesthesia and understands the risks and complications as described. The informed consent for anesthesia should include a discussion of what to expect from the administration of anesthesia and possible adverse effects and risks. A number of issues should be discussed routinely, including timing of surgery, premedication, risks of dental injury, cardiac risks, sequence of events prior to anesthesia induction, awakening from anesthesia, presence of catheters, duration of time in the PACU, anticipated return to a hospital bed or discharge, postoperative pain management, and the likelihood of nausea and vomiting. Patients may have questions concerning perioperative awareness. Rather than cause undue worry, clinical judgment should dictate how detailed a description of each of these issues should be for each patient.
Choice of Anesthesia
Considerations in choosing an anesthetic technique include the planned surgical procedure, positioning requirements, patient preferences, surgeon preferences, the urgency of the operation, postoperative pain management, and potential for admission to a critical care unit. Some procedures (eg, thoracotomy) cannot be performed under a regional anesthetic or neuraxial blockade and necessitate a general anesthetic. Other procedures (eg, extremity surgery) can be performed under regional, neuraxial, or general anesthesia. Sometimes a combination of an epidural and a general anesthetic may be chosen with continuation of the epidural for postoperative pain management. Emergency surgery for patients with a full stomach may necessitate a rapid-sequence general anesthetic to protect from pulmonary aspiration. Regional anesthesia may provide anesthesia for hip surgery but may not provide much in the way of patient comfort because of the position requirements of a fracture table. Patient age and preference must also be included in the decision of choice of anesthetic technique. However, some regional anesthesia may be contraindicated for patients with the peripheral neuropathy of diabetes. Notation of the proposed type of anesthesia must be entered into record of the preanesthesia evaluation.
Holding Room & Operating Room
The nurse, surgeon, and anesthesiologist have many tasks to perform, starting in the holding area before the surgery can begin. The nurse checks the patient in and records vital signs, checks for a signed consent, and starts an intravenous line if needed. The surgeon should confirm and mark the site of surgery. The anesthesiologist should confirm the preoperative evaluation and type of anesthetic selected.
Wrong Site Surgery
In July 2004, the Joint Commission on the Accreditation of Healthcare Organizations (JCAHO) instituted a patient safety mandate known as the Universal Protocol for preventing wrong site, wrong procedure, wrong person surgery. All members of the care team must be familiar with and always participate in and perform the following three steps of this Universal Protocol.
Step 1: Initial verification of the intended patient, procedure, and site of the procedure. This step begins at the time the procedure is scheduled and again at the time of admission into the medical facility, anytime care responsibility is transferred to another caregiver, and before the patient leaves the preoperative area for the operating room.
Step 2: Marking the operative site. An unambiguous mark must be made using a marker that is sufficiently permanent to be visible after surgical prep and draping on or near the intended surgical incision site. This mark should not be an X, as in “X marks the spot,” but rather a word or line representing the proposed incision. This mark must be made by the surgeon performing the procedure. If possible, the patient should participate when the site is marked.
Step 3: The time out immediately before starting the procedure. A time out must be conducted in the location where the surgical procedure will be done, and all members of the care team—surgeon, nurses, anesthesiologists—must actively participate in verification of correct patient identity, correct side and site of surgery, agreement on the scheduled procedure, and assurance that all of the necessary implants and special equipment are immediately available. This time out must take place before incision. JCAHO requires that the time out be documented in the medical record.
Joint Commission on the Accreditation of Healthcare Organizations: Universal protocol for preventing wrong site, wrong procedure, wrong person surgery. Available at:www.jointcommission.org/patientsafety/universalprotocol. Accessed November 28, 2008.
The Operating Room
The anesthesiologist must check the equipment in the operating room before helping to transport the patient. Once in the operating room, the patient is transferred to the operating table with the assistance of the nurses and anesthesiologist. It is standard anesthesia practice to apply monitors to measure arterial blood pressure (a-line, blood pressure cuff), heart rate, oxygenation (pulse oximeter), and ventilation (capnography) before induction of anesthesia (Table 11–5).
Table 11–5. Standards for basic anesthesia monitoring.
The anesthesiologist must be certain that a surgeon is present in the room before beginning induction. The final time out should then be performed, confirming site, patient, procedure, and surgical personnel.
General Anesthesia Management
Patients will be preoxygenated before induction of a general anesthetic. General anesthesia is commonly induced by administration of intravenous drugs (eg, propofol or thiopental) and, in cases when cardiovascular status is compromised, etomidate or ketamine. Patients receiving propofol may complain of discomfort at the IV sites, and patients receiving etomidate may have some athetoid movements that appear seizurelike. Almost all anesthetics are preceded by the administration of an opiate (eg, fentanyl) in a dose that is not intended to induce an anesthetic but that helps reduce the amount of induction agent. Most general anesthetics then include a muscle relaxant to facilitate endotracheal intubation. Tracheal intubation is almost always performed during general anesthesia and is especially important for patients presenting for emergent surgery with presumed full stomach or when positive pressure ventilation is required. The laryngeal mask airway (LMA) can also be used to maintain a patent airway. To minimize the time that the trachea is unprotected, a rapid-sequence induction of anesthesia using rapid administration of induction agent and rapid-acting muscle relaxant (eg, succinylcholine) can be utilized. The “crash induction” is a modification of this rapid-sequence technique with the application of cricoid pressure by a caregiver other than the inducing anesthesia personnel.
General anesthesia may also be induced by mask using an inhalation anesthetic (eg, isoflurane or sevoflurane). This method is commonly used for children. Once adequate depth of anesthesia is assured, a muscle relaxant may be administered to help facilitate endotracheal intubation. Inhalation induction takes longer than rapid-sequence induction, and the airway may be unprotected for a longer time. A combination of inhalation agent and intravenous agent can also be used to induce general anesthesia.
Once an adequate depth of anesthesia and adequate muscle relaxation is attained, the trachea is intubated. Ease of endotracheal intubation can usually be predicted from the careful preoperative airway evaluation.
However, the anesthesiologist occasionally encounters an unexpected difficult intubation and additional maneuvers may be necessary: These can include cricoid manipulation, adjustment of the patient’s head position, or use of a long, stiff catheter (eg, a bougie) or a fiberoptic bronchoscope. The American Society of Anesthesiologists provides an algorithm for the management of the difficult airway. If another provider is placing cricoid pressure, the anesthesiologist must directly state what maneuver would be the most helpful. If the airway cannot be secured after multiple attempts, patients can be awakened and a decision made to proceed with an awake fiberoptic intubation or to cancel the anesthetic until further workup can be performed. The most serious complication of endotracheal intubation, and the most common cause of serious anesthesia morbidity and mortality, is the failure to secure the airway. Other common complications are dental injuries, soft tissue injury to the lips, hypertension and tachycardia, and laryngospasm on extubation.
Following anesthetic induction, the patient must be properly positioned for the procedure. It is the responsibility of both surgeon and anesthesiologist to assure that the patient is positioned to avoid physical or physiologic complications. The American Society of Anesthesiologists’ closed claims study notes that nerve damage from malpositioning during surgery is the second most common anesthetic complication. Careful attention must be paid to adequately protect all potential pressure and vulnerable areas such as elbows, knees, heels, and eyes. The ulnar nerve is particularly susceptible to injury, as is the brachial plexus when patient’s arms are abducted too far. Hemodynamics may also be compromised by position changes that may result in decreased venous return and resultant hypotension.
American Society of Anesthesiologists: Practice guidelines for management of the difficult airway: an updated report by the American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Anesthesiology. 2003; 98:1269.
Cheney FW et al: Nerve injury associated with anesthesia: a closed claims study. Anesthesiology. 1999;90:1062.
Maintenance of General Anesthesia
Once the airway is safely secured, anesthesiologists commonly maintain the anesthetic with a combination of an inhalation agent, nitrous oxide, opiate, and muscle relaxant. This “balanced anesthetic” allows for titration of agents to maintain the requirements of anesthesia: analgesia, amnesia (unconsciousness), skeletal muscle relaxation, and control of the hemodynamic responses to surgical stimulation. Drugs with specific pharmacologic profiles are chosen to help satisfy the anesthetic requirements. Analgesia is provided by opiates and inhalational agents; amnesia is provided by benzodiazepines, nitrous oxide, and inhalation agents; and muscle relaxation is provided by neuromuscular blocking drugs, inhaled agents, or local anesthetics. The provision of the right amount of muscle relaxation to facilitate the procedure but not too much to obscure a clinical sign of anesthetic depth or to result in prolonged relaxation postoperatively presents a challenge to the anesthesiologist. A peripheral nerve stimulator can monitor muscle relaxation such that the relaxant is reversible at the end of the case to allow for safe extubation.
Regional Anesthesia for Surgery
Many operations require no general anesthetic. These include almost any procedure done below the waist, on lower abdomen, and on the upper extremities. Spinal or epidural anesthesia provide excellent muscle relaxation, profound analgesia, and avoidance of airway manipulation, and allows the patient to be conscious. Spinal or epidural anesthesia have additional advantages: decreased blood loss during orthopedic procedures, fewer thrombotic complications, less pulmonary compromise, maintenance of vasodilatation for postoperative vascular surgeries, earlier hospital discharge, and avoidance of immune response compromise.
Most spinal anesthetics are performed in either the lateral position or with the patient sitting on the operating table. Following sterile prep and local skin anesthetic, a small 25-27 gauge spinal needle is introduced in the lower lumbar spine, and the subdural space is identified by the presence of cerebrospinal fluid (CSF). Depending on the planned length of surgery, either lidocaine or bupivacaine (with or without epinephrine or an opiate) is injected. Lidocaine spinal anesthesia provides at most 2 hours of anesthesia, while bupivacaine provides up to 5 hours of anesthesia. However, due to patient discomfort from tourniquet break-through pain, the use of orthopedic tourniquets limits the usefulness of spinals no matter which local anesthetic is used to no more than 2 hours. Once the local agent is injected, patients are placed in the supine position for 5-10 minutes to allow for proper spread of the local anesthetic. During this time, blood pressure and heart rate are monitored; both hypotension and bradycardia can be induced by a sympathectomy due to the cephalad spread of the local. During this 5-10 minute period, patient movement should be limited. Once the block has stabilized, the surgical preparation and positioning can proceed. The anesthesiologist monitors the patient in the same manner as for general anesthesia and administers sedation as needed.
Other than expected hemodynamic changes, the most common complication of spinal anesthesia is postspinal headaches. The incidence is very low when smaller-gauge spinal needles are used and are more common in young women. The spinal headache is almost always positional and abates when the patient is recumbent. Severe headaches can result in diplopia because of stretching of the sixth cranial nerve as the brain sinks from loss of CSF. Patients usually complain of the headache a day or two following the operation. Conservative treatment is the maintenance of adequate hydration, remaining recumbent, and an analgesic such as acetaminophen. Severe headache may require a “blood patch” to plug the leak of CSF and is performed by an anesthesiologist.
Epidural anesthesia has several distinct differences from spinal anesthesia. The epidural space is between the ligamentum flavum and the dural structures; in placing an epidural, the subdural space is not entered, so no CSF leak is created with the potential for a spinal headache. The epidural anesthetic may be continued by insertion of a small catheter into the epidural space. Additional local anesthetic can be added to move the block to higher spinal levels or to maintain the selected level of anesthesia. This continuous epidural technique can be used for postoperative pain control. The catheter can be placed at spinal levels in the midthoracic region for thoracotomy or lower thoracic or lumbar region for abdominal operations or lower extremity procedures. Epidural anesthesia requires the administration of high volumes of local anesthetics. There is the potential for intravascular injection with resultant cardiovascular compromise or high block. There is also the potential for misplacement of the catheter or epidural needle in the subarachnoid space. Instillation of the larger volumes of local in the subarachnoid space can result in a total spinal or high block with resultant cardiovascular collapse. Therefore, small test doses of local anesthetic are administered to evaluate for signs of intravenous injection or high block. Another potential disadvantage of epidural anesthesia is that the onset is much slower than spinal anesthesia. The same hemodynamic changes observed with epidural can occur with spinals.
A common complication of both spinal and epidural anesthesia is prolonged blockade of parasympathetic fibers that innervate the bladder with resultant urinary retention and the need for a urinary bladder catheter.
True regional anesthesia is useful for procedures on the extremities. Useful anesthesia of the upper extremity can be obtained by blockade of the brachial plexus using an interscalene approach, a supraclavicular approach, or an axillary approach. Lower extremity surgery may be performed utilizing blockade of the lumbar plexus and its major branches: femoral nerve, sciatic nerve, lateral femoral cutaneous nerve, obturator nerve, and popliteal nerve. In some instances, a catheter can be placed near the nerve or plexus to allow for continuous blockade and postoperative pain control. The usefulness of these blocks for extremity surgery is limited in time by the use of tourniquets if the patient is to remain awake during the procedure. These blocks are very useful if avoidance of a general anesthetic is desired. Additional advantages of peripheral nerve blocks include earlier discharge from recovery areas and return to home, lack of administration of large doses of opiates, less nausea and vomiting, no instrumentation of patient airway, and earlier ambulation. Intraoperative sedation may be provided, and the anesthesiologist monitors the patient in the standard manner.
Monitored Anesthesia Care
Monitored anesthesia care (MAC) was previously termed local anesthesia with standby. The “standby” is an anesthesia caregiver who monitors the patient’s status while the surgeon performs a procedure under local anesthesia. The anesthesiologist can also provide sedation and analgesia as needed for the patient. This type of anesthesia is usually requested by the surgeon for patients who may be especially frail in health; it provides the option to convert to a general anesthetic if necessary.
Completion of Surgery
At the end of the procedure, most often patients who have been intubated for the surgery have their muscle relaxation reversed and the anesthetic depth decreased to allow them to return to consciousness. Once the return of muscle function has been assured and the patient is able to respond to commands, the endotracheal tube can be removed and the patient closely observed to ensure adequate ventilation. Patients are then transferred to a stretcher and transported to the PACU, accompanied by a member of the anesthesia care team who monitors the patient’s condition during transport. Many institutions require that a member of the surgical team also accompany the patient to the PACU along with the anesthesiologist. Some critically ill patients are transported directly to the intensive care unit (ICU), still intubated, sedated, and ventilated.
Postanesthesia Recovery Room
The PACU, most commonly known as the recovery room, is where most patients are transferred after surgery. The PACU is the designated area in which patients receive postanesthesia monitoring of vital signs as well as the beginning of the nursing care for their surgical recovery. It is the standard of the American Society of Anesthesiologists that all patients, regardless of the type of anesthesia, receive appropriate postanesthesia care, either in a PACU or an equivalent area such as a critical care unit. An exception to this standard can only be made by the anesthesiologist responsible for the patient’s care. Once in the PACU, a verbal report is provided to the responsible PACU nurse by a member of the anesthesia care team who is familiar with and who accompanied the patient during transport. The surgeon can also give a report as to the surgical issues that may impact on the patient’s recovery.
The PACU is equipped with essentially the same monitors as the operating room and with the drugs and equipment needed for emergency resuscitation. The PACU is a specialized, short-stay ICU. PACUs are staffed with specially trained nurses to monitor patients who are recovering from the anesthetic. Patients are continually monitored in the PACU for approximately 1 hour or until they fulfill specific objective criteria. Discharge from the PACU requires the clinical judgment of the PACU team. Particular attention is focused on the monitoring of oxygenation, ventilation, circulation, level of consciousness, and temperature.
Most PACUs use a discharge scoring system (egg, the Aldrete score) describing objective criteria that must be fulfilled before the patient can be discharged from the PACU. These criteria include quantitative analysis of patient’s ability to move extremities in response to verbal commands, adequacy of ventilation (pulse oximetry) circulation (stable vital signs) level of consciousness, and pain control. After outpatient surgery, patients must have an adult to escort them home. Most institutions have policies requiring that anesthesiologists, in conjunction with the PACU nursing team, discharge patients from PACU.
Aldrete JA, Kroulik D: A postanesthetic recovery score. Anesth Analg. 1970;49:924.
Awad JT, Chung F: Factors affecting recovery and discharge following ambulatory surgery. Can J Anaesth. 2006;53:858.
COMMON POSTOPERATIVE PROBLEMS
There are many reasons why patients have other than a routine stay in the PACU. The three most common PACU problems are hypothermia, nausea and vomiting, and pain control. Hypotension/hypertension, hypoxemia, hypercapnia/hypoventilation, and agitation can also occur.
Hypothermia
A very common complication of anesthesia and surgery is hypothermia. Every effort should be made in the operating room to avoid patients becoming hypothermic, even if this requires that the operating room temperature is maintained at a warmer-than-comfortable level. Patients who are admitted to the PACU and are hypothermic must be rewarmed to avoid the adverse consequence of shivering (ie, increased oxygen consumption). Hypothermia may also have an adverse effect on coagulation parameters and may delay recovery from anesthesia due to decreased drug metabolism. The most effective methods of rewarming are forced-air warming devices or water-jacket devices. Shivering can be actively treated with small doses of meperidine.
Rajagopalan S et al: The effects of mild perioperative hypothermia on blood loss and transfusion requirement. Anesthesiology. 2008;108:71.
Postoperative Nausea & Vomiting
According to the Society of Ambulatory Anesthesia (SAMBA), untreated, postoperative nausea and vomiting (PONV) occurs in 20%-30% of the general surgical population and up to 70%-80% in the high-risk surgical population. The increased PACU stays and sometimes hospital admission to control PONV adds to patient discomfort and morbidity and adds a financial burden to the health care system. SAMBA’s seven guidelines have been adopted by many health care facilities for the prevention and treatment of PONV.
Gan TJ et al: Society for Ambulatory Anesthesia guidelines for the management of postoperative nausea and vomiting. Anesth Analg. 2007;1051:615.
Postoperative Acute Pain Management
The management of postoperative surgical pain is the responsibility of both the anesthesiology and surgery services. Other than PONV, inadequate postoperative pain control is a primary cause of unanticipated hospital admission for outpatient surgery. The severity of the pain is usually site dependent (upper abdominal procedures tend to be more painful than lower abdominal procedures; ie, appendectomy is more painful than inguinal hernia, which is more painful than minor chest wall surgery), but the individual patient’s response to the pain and efforts to treat it vary widely. What may appear to be a minor incision to some may be very painful to others. The clinical challenge of providing adequate postoperative pain management is also a major mandate by JCAHO and the national media. Thus, almost every anesthesia department has an acute pain management team that can help with the management of patients in PACU and later in the surgical intensive care or general care unit.
Morphine has been the historical postoperative analgesic, administered either intramuscularly or intravenously. Patient response to a standardized administration protocol is variable, however, and can fail to control pain or cause symptoms of overdosage. Every patient is different in the required serum concentration of drug that results in adequate pain control.
There are four common modalities or approaches to postoperative pain management:
Oral medications. For minor procedures, for example, excision of skin lesions, nonsteroidal analgesics may be sufficient. For more intense levels of pain, oral narcotics in combination with acetaminophen are often effective.
Intravenous opioids. Occasionally, one or two intravenous doses of morphine, hydromorphone, or fentanyl may be sufficient to control postoperative pain. However, a more reliable method is the administration of small doses of narcotic given on demand by the patient. Patient-controlled analgesia (PCA) uses the same or even less total narcotic to control pain and is as safe as intramuscular medications. Patients are instructed on how to use the PCA device to administer narcotic on demand. PCA has widespread acceptance by patients, physicians, and nurses because it provides pain control in a timely manner that more closely matches the patient’s requirements. Caution must be used when pain control appears to be inadequate and house staff covering the patient are tempted to give an intravenous “boost” of narcotic.
Epidural opiate analgesia. The application of opioids or narcotics at the neuraxial receptor sites via an epidural catheter is probably the modality of choice for severe acute postoperative pain control. An epidural catheter is preferably placed preoperatively at a spinal dermatome level close to the site of incision: midthoracic level for thoracic surgeries, lower thoracic for upper abdominal surgeries, or lumbar for lower abdominal incisions or lower extremity surgeries. This technique utilizes a continuous infusion of a combined solution of a low concentration of local anesthetic (bupivacaine 0.125 mg/cc) and an opioid (morphine, hydromorphone, or fentanyl). This modality does not require patient cooperation but can be used in a PCA mode. Epidural analgesia can be continued for multiple days; it has beneficial effects for maintaining peripheral vasodilatation after vascular procedures and improving respiratory mechanics due to reduced pain when patients are breathing on their own. Patients must be monitored for respiratory depression while receiving epidural analgesia, as respiratory depression is the major complication from this pain control therapy.
Specific nerve or plexus block. Local anesthesia block of single nerves or continuous catheter infusion of local anesthetic around major nerve plexuses is becoming more popular. Examples include single injection or placement of a continuous catheter around the femoral nerve for controlling pain from knee surgery and continuous catheters around the brachial plexus (usually supraclavicular) for controlling pain from upper extremity surgery.
Complications of Anesthesia
No matter how well patients are prepared for anesthesia and surgery, there is always the possibility of a complication from the delivery of anesthesia. These complications can be minor in nature (eg, intravenous infiltration, hypothermia, or minor ocular injury) or major issues (eg, an unanticipated difficult airway that may result in significant morbidity or death). Many complications are preventable with good preoperative preparation, but some are not preventable (unexpected drug reactions or metabolic crisis, eg, malignant hyperthermia). Four common complications are anesthesia awareness, peripheral nerve injury, malignant hyperthermia, and visual loss.
Awareness
Many patients are concerned about being aware during the surgical procedure. Intraoperative awareness under general anesthesia is rare with a reported incidence of 0.1%-0.2%. Intraoperative awareness does occur and can lead to significant psychological sequelae and extended disability for the patient. Certain types of surgery have a higher incidence of intraoperative awareness, including cardiac surgery, major trauma, and obstetrics. All are associated with critical or life-threatening situations of hemodynamic compromise that make awareness unavoidable if the caregiver is to achieve other critical anesthetic goals of maintaining cardiac, respiratory, and vascular homeostasis. The Practice Advisory from the American Board of Anesthesiologists defines intraoperative awareness: “When a patient becomes conscious when a surgical procedure is performed under a general anesthetic and subsequently has (explicit) recall of these events.” The Advisory notes that the recall does not include the time before the general anesthetic is induced or the time of intentional emergence and return to consciousness.
Strategies suggested to lessen or eliminate the risk of intraoperative awareness include the following:
3a. Intraoperative monitoring. The currently accepted strategy is to utilize all the standard anesthesia patient monitors (EKG, blood pressure measurements, heart rate monitors, continuous agent analyzers, and capnography) and to intermittently assess for purposeful or reflex movement to detect intraoperative consciousness. There are instances in which there were no reported changes in vital signs in patients who have reported recall.
3b. Monitoring brain electrical activity. Several monitoring devices are claimed to be able to interpret data from the processed, raw electroencephalogram of patients and correlate it to the depth of anesthesia and thus help prevent recall under general anesthesia. The commonest device currently available is known as the bispectral index monitor (BIS; Aspect Medical Systems, Natick, MA). Currently, the use of BIS for patients undergoing general anesthesia has not been shown to offer any advantage over a protocol that uses end-tidal anesthetic agent concentrations in decreasing the incidence of intraoperative awareness.
In conclusion, when awareness occurs, either reported spontaneously by the patient in the postoperative period or elicited during the postoperative visit by the anesthesiologist, the patient’s report must be taken seriously. Some patients will require significant counseling and treatment postoperatively, and caregivers should be sensitive to the potential issue and offer any help requested.
American Board of Anesthesiologists: Practice advisory for intraoperative awareness and brain function monitoring. Anesthesiology. 2006;104:847.
Avidan MS et al: Prevention of intraoperative awareness in a high-risk surgical population. N Engl J Med. 2011;591-600.
Peripheral Nerve Injury
Peripheral nerve injury is a known complication of anesthesia and can occur under general anesthesia or a regional technique. These injuries are almost always due to patient positioning and the patient’s inability to report and respond to abnormal pressure points or awkward position of an extremity. The ulnar nerve at the elbow is the most common injury and occurs even if the patient has had what was felt to be adequate padding provided for protection. Other peripheral nerves that are less commonly injured include the peroneal nerve at the knee and the radial nerve as it passes through the spiral grove of the humerus. The peroneal nerve is typically injured by abnormal position against a lithotomy stirrup, and the radial nerve is injured by a blood pressure cuff or abnormal pressure from surgical towels. Patients usually report numbness along the course of the nerve, but some motor weakness may also occur. These injuries usually resolve in a short time period. Abnormal stretching of the brachial plexus from extreme abduction of the arms, improperly placed shoulder braces, or chest wall retractors during cardiac surgery may result in more serious injuries, including not only sensory but motor loss that may not recover as rapidly or completely as the ulnar, radial, or peroneal nerves. More severe injuries that involve motor loss need to have a baseline examination established and therapy started. Since most of these peripheral nerve injuries are due to malpositioning during surgery, it is the responsibility of surgeons, nurses, and anesthesiologists to adequately position patients and provide sufficient padding or other protection.
Welch MB, Brummett CM, Welch TD, et al: Perioperative peripheral nerve injuries: a retrospective study of 380,680 cases during a 10-year period at a single institution. Anesthesiology. 2009;111:490-497.
Malignant Hyperthermia
Malignant hyperthermia is a rare, genetically inherited disease characterized by intense muscle contraction. It results from an uncontrolled release of calcium from the sarcoplasmic reticulum and massive increase of intracellular calcium in skeletal muscle due to the inability of the calcium to be reabsorbed. This intense muscle contraction leads to a hypermetabolic state manifest by hyperthermia, hypercapnia, tachycardia, and metabolic acidosis. It is fatal if untreated. Malignant hyperthermia is commonly triggered by the administration of anesthetic agents; the depolarizing muscle relaxant succinylcholine alone or in conjunction with a volatile agent. The more modern anesthetic vapors sevoflurane and desflurane are less frequently implicated as triggers. Early clinical manifestations of malignant hyperthermia include unexplained tachycardia and metabolic acidosis, but temperature elevation may be a late finding. Although not always reliable, the earliest sign of malignant hyperthermia is sometimes masseter spasm following the administration of succinylcholine during induction. Careful monitoring must always ensue. Relying on temperature elevation alone is dangerous, and arterial blood gases must be monitored for unexplained metabolic acidosis. In some patients, malignant hyperthermia develops insidiously during the surgery, and temperature elevation can be the first manifestation.
Malignant hyperthermia is treatable and preventable. The treatment of choice is intravenous dantrolene. Every operating room must have a malignant hyperthermia protocol and a kit that includes multiple doses of dantrolene. Dantrolene is supplied as a powder and requires several minutes to mix it into a useable intravenous solution. Malignant hyperthermia is a true anesthesia emergency, and the anesthesiologist will require assistance from the operative team. The surgical procedure may have to be postponed. Successful treatment of malignant hyperthermia is the usual outcome. Patients should be monitored in a critical care unit for 24 hours or until stable and referred for confirmatory testing.
Malignant hyperthermic reactions can be prevented. Any patient with a personal or family history of malignant hyperthermia should be administered a completely nontriggering anesthetic without relying on succinylcholine or volatile agents.
Hopkins PH: Malignant hyperthermia. Trends Anaesthes Crit Care. 2008;19(1):22-33.
Perioperative Visual Loss
A recently described complication of prolonged (> 6.5 hours) spinal surgical procedures performed in the prone position, associated with large blood losses, is partial or complete visual loss. Vision loss seems to be associated with an ischemic optic neuropathy without any known etiology. There does not seem to be any identifiable pre-op patient characteristic. Intraoperative management for patients undergoing prolonged procedures involving substantial blood loss include continuous blood pressure monitoring and CVP monitoring. There is no consensus on lower limits of hematocrit, limits of vasopressors, or prone positioning. There is no known treatment. The risk of visual loss should be discussed with patients in the preoperative phase of surgery and anesthesia for those operations that require prone positioning.
Apfelbaum JL et al: Practice Advisory for Perioperative Visual Loss Associated with Spine Surgery. An Updated Report by the American Society of Anesthesiologists Task Force on Perioperative Visual Loss. Anesthesiology. 2012;116:274-285.
MULTIPLE CHOICE QUESTIONS