Ophthalmol Clin N Am 19 (2006) 179 – 191
General Anesthesia for Ophthalmic Surgery Kathryn E. McGoldrick, MDa,b,T, Peter J. Foldes, MDb a
Department of Anesthesiology, New York Medical College, Valhalla, NY 10595, USA b Westchester Medical Center, Valhalla, NY 10595, USA
Anesthetic management plays a vital role in contributing to the success or failure of ophthalmic surgery. Patients with eye conditions are often at the extremes of age, ranging from tiny, fragile infants with retinopathy of prematurity or congenital cataracts to nonagenarians with submacular hemorrhage, and may have extensive associated systemic or metabolic diseases [1]. Moreover, with more than 13% of Americans characterized as elderly (older than 65 years), we must acknowledge that the increased longevity typical of developed nations has produced a concomitant increase in the longitudinal prevalence of major eye diseases, including diabetic retinopathy, primary open-angle glaucoma, and age-related macular degeneration [2]. Clearly, the challenges of caring for an aging population with complex coexisting diseases undergoing sophisticated and technically demanding ophthalmic procedures require a high level of anesthetic expertise. The objectives of anesthesia for ophthalmic surgery include safety, akinesia, satisfactory analgesia, minimal bleeding, avoidance or obtundation of the oculocardiac reflex, prevention of intraocular hypertension, and awareness of potential interactions between ophthalmic drugs and anesthetic agents. Other exigencies include an understanding of the anesthetic implications intrinsic to delicate ophthalmic procedures, including the necessity for an especially smooth induction, maintenance, and emergence from anesthesia. Indeed, a closed claims analysis by Gild
T Corresponding author. Westchester Medical Center, Macy Pavilion, Room 2389, Valhalla, NY 10595. E-mail address:
[email protected] (K.E. McGoldrick).
and colleagues [3] disclosed that 30% of eye injury claims related to anesthesia management were associated with patient movement during ocular surgery. Most of the problems transpired during general anesthesia, but in one fourth of the cases the patients were receiving monitored anesthesia care during procedures performed under local or regional anesthesia. Tragically, the outcome was blindness in all cases. Clearly, strategies to ensure patient immobility during ophthalmic surgery are mandatory. Moreover, safety issues are complicated by the logistic necessity for the anesthesiologist frequently to be positioned at a considerable distance from the patient’s face, thus preventing immediate, direct access to the airway. It is axiomatic that open, clear, and effective communication among the anesthesiologist, ophthalmologist, and patient is integral to optimal outcome of ophthalmic surgery.
Indications for general anesthesia In selecting the anesthetic technique for eye surgery, numerous issues must be considered. General anesthesia remains the technique of choice for children, mentally retarded individuals, and demented or psychologically unstable patients. It is also the favored technique for patients with suspected or apparent open-globe injuries, although recent literature supports the use of regional eye blocks in selected patients with open-eye trauma. Recognizing that there are several distinct permutations of eye injuries, Scott and colleagues [4] developed techniques to safely block patients with certain open-globe injuries. In a 4-year period, 220 disrupted eyes were repaired via regional anesthesia at Bascom Palmer Eye Institute.
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Many of these injuries were caused by intraocular foreign bodies and dehiscence of cataract or corneal transplant incisions. Blocked eyes tended to have smaller, more anterior wounds than those repaired via general anesthesia. There was no outcome difference—that is, change of visual acuity from initial evaluation until final examination—between the eyes repaired with regional versus general anesthesia. Additionally, combined topical analgesia and sedation for selected patients with open-globe injuries has also been reported [5]. General anesthesia is the technique of choice for removal of infected scleral buckles or for patients with very high myopia, where a perforating injury from peribulbar or retrobulbar block is feared. Other indications may include claustrophobia, deafness, a language barrier, Parkinson’s disease, and intractable arthritis or orthopnea, which impair the patient’s ability to lie flat and remain motionless during surgery. Furthermore, the anticipated duration of the procedure must be factored into the selection process, because few geriatric patients under regional anesthesia can remain comfortable on a narrow, hard operating table for procedures that exceed 2 or 3 hours. With general anesthesia the risks of retrobulbar or peribulbar hemorrhage, globe perforation, myotoxicity, central spread of local anesthetic with possible brain stem anesthesia, and inadequate intraoperative analgesia are virtually eliminated. Nonetheless, general anesthesia may be associated with a greater likelihood of airway complications and postoperative nausea and vomiting. Although regional and topical anesthetic techniques have gained enormous popularity in recent years, it is imperative to appreciate the vital role that general anesthesia maintains in the care of certain ophthalmic patients. Major retrospective and prospective nonrandomized studies have failed to demonstrate the superiority of one anesthetic approach over the other in terms of morbidity and mortality [6 – 10]. Accordingly, the risks, benefits, and alternatives of all anesthetic options should be explained clearly to the patient, with the choice determined after discussion among patient, anesthesiologist, and surgeon.
Preoperative evaluation The preoperative evaluation of the geriatric patient characteristically is more complex than that of the younger patient owing to the heterogeneity of seniors and the increased frequency and severity of comorbid conditions associated with aging. The process of aging is highly individualized. Different people age at
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varying rates and often in different ways. Typically, however, virtually all physiologic systems decline with advancing chronological age. Nevertheless, chronological age is a poor surrogate for capturing information about fitness or frailty. Moreover, perioperative functional status can be difficult to quantitate because many elderly patients have reduced preoperative function related to deconditioning, ageassociated disease, or cognitive impairment. Thus, it is challenging to satisfactorily evaluate the patient’s capacity to respond to the specific stresses associated with anesthesia and surgery. How, for example, does one determine cardiopulmonary reserve in a patient severely limited by osteoarthritis and dementia? Even ‘‘normal’’ aging results in alterations in cardiac, respiratory, neurologic, and renal physiology that are linked to reduced functional reserve and ability to compensate for physiologic stress. Moreover, the consumption of multiple medications so typical of the elderly can alter homeostatic mechanisms. Preoperative testing In the general population there is strong consensus that most so-called ‘‘routine’’ tests are not indicated. In the subset of geriatric patients our knowledge is somewhat more limited. Nonetheless, a recent study on routine preoperative testing in more than 18,000 patients undergoing cataract surgery is worthy of comment. Patients were randomly assigned to undergo or not undergo routine testing (ECG, complete blood cell count, electrolytes, serum urea nitrogen, creatinine, and glucose) [11]. The analysis was stratified by age and disclosed no benefit to routine testing for any group of patients. Similar conclusions were drawn in a smaller study of elderly noncardiac surgical patients by Dzankic and colleagues [12]. Some physicians and lay people, however, misinterpreted the results of Schein and colleagues’ [11] study, believing that patients having cataract surgery need no preoperative evaluation. It is vital to note that all patients in this trial received regular medical care and were evaluated by a physician preoperatively; they simply were not subjected to a robotic battery of routine laboratory testing. Patients whose medical status indicated a need for preoperative laboratory tests were excluded from the study. Because ‘‘routine’’ testing for the more than 1.5 million cataract patients in the United States is estimated to cost $150 million annually, the favorable economic impact of this ‘‘targeted’’ approach is obvious. From these investigations and others, a few concepts emerge. First, routine screening in a general population of elderly patients does not significantly
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augment information obtained from the patient’s history and physical examination. Testing should be selective, based on abnormalities found from the patient’s history and physical examination. Second, the positive predictive value of abnormal findings on routine screening is limited. Third, positive results on screening tests have modest impact on patient care. The preoperative period is not the appropriate time to screen for asympotomatic disease. The dearth of population studies of perioperative risk and outcomes specifically addressing the geriatric population can make selecting the most appropriate course of care challenging. Because age itself adds very modest incremental risk in the absence of comorbid disease, most risk-factor identification and risk-predictive indices have focused on specific diseases [13 – 15]. Considerations for patients with cardiac disease It is well known that normal aging produces structural changes in the cardiovascular system, as well as changes in autonomic responsiveness/control, that can compromise hemodynamic stability. The superimposition of such comorbid conditions as angina pectoris or valvular heart disease can further impair cardiovascular performance, especially in the perioperative period. According to the guidelines of the American College of Cardiology (ACC) and the American Heart Association (AHA) for preoperative cardiac evaluation, the patient’s activity level, expressed in metabolic units, is a primary determinant of the necessity for further evaluation, along with the results obtained from history and physical examination [13]. These findings are then evaluated in conjunction with due consideration for the invasiveness of the planned surgical procedure. Fortunately, most ophthalmic procedures are typically considered to represent relatively noninvasive, low-risk surgery. Clearly, the goal of the preoperative evaluation should be the identification of major predictors of cardiac risk such as unstable coronary syndromes (for example, unstable angina or myocardial infarction [MI] less than 30 days ago), decompensated congestive heart failure (CHF), severe valvular disease, and significant arrhythmias. These patients have a prohibitive rate of perioperative morbidity and mortality, and are inappropriate candidates for elective outpatient surgery. They deserve the benefit of further cardiology consultation and optimization. In patients with intermediate clinical predictors (mild angina, previous MI more than 30 days ago, compensated or prior CHF, diabetes mellitus, or renal insufficiency),
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the invasiveness of the surgery and the functional status of the patient will play major roles in determining the nature and extent of preoperative testing or intervention. Importantly, no preoperative cardiovascular testing should be performed if the results will not change perioperative management. Patients with minor clinical predictors, such as advanced age, ECG abnormalities, rhythm other than sinus, low functional status, history of stroke, or hypertension, who are having low- or intermediate-risk surgery typically will not require further cardiovascular testing. For those in whom further testing is warranted, there are several options including Holter monitoring, radionuclide ventriculography, thallium scintigraphy, dobutamine stress echocardiography, and coronary angiography. The use of perioperative b-blockade in intermediate or high-risk patients undergoing vascular surgery can be beneficial and may obviate the need for more invasive interventions [16]. A recent study demonstrated that perioperative b-blocker therapy is associated with a reduced risk of inhospital death among high-risk, but not low-risk, patients undergoing major noncardiac surgery [17]. However, there is an absence of data pertaining to the use of perioperative b-blockade in patients undergoing less invasive outpatient surgery that is characteristic of most ophthalmic procedures. Increasingly, patients with coronary artery disease are undergoing stent placement. A frequently asked question in this context is how long should one wait after stent placement before scheduling a patient for elective surgery under general anesthesia. Kaluza and colleagues [18] in 2000 published a recommendation (based on a study of 40 patients) that elective surgery should be postponed for 2 to 4 weeks after stent placement to allow completion of the antiplatelet protocol. A few years later, however, Wilson and colleagues [19] studied more than 200 patients and recommended that nonemergency surgery should be delayed for 6 weeks after stent insertion to permit completion of the antiplatelet therapy and to allow for endothelialization of the stent. It should be emphasized that diabetes mellitus is an intermediate predictor of such adverse cardiac outcomes as perioperative MI and CHF after elective surgery because of the accelerated atherosclerosis that occurs with associated aberrations of lipid and cholesterol metabolism. The Diabetes Control and Complications Trial, a clinical study of young (average age 27 years) diabetic patients, showed that intensive treatment delayed the onset and severity of retinopathy, nephropathy, and neuropathy [20]. However, the cohort was probably too young to demonstrate a
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reduction in cardiovascular complications with aggressive insulin therapy, but the results suggest that a well-controlled diabetic patient may be at lesser risk than a poorly controlled diabetic patient. Nonetheless, this issue is not addressed in the ACC/AHA guidelines. It is important to appreciate that the diagnosis of myocardial ischemia may be more challenging in a diabetic patient owing to the high incidence of autonomic neuropathy. Patients with autonomic neuropathy may not complain of chest pain even when experiencing an acute MI.
General anesthesia: physiologic principles and pharmacologic agents Those patients who require or prefer general anesthesia for eye surgery experience a favorable outcome provided the airway is satisfactorily maintained, hemodynamic stability is achieved, and the eye is kept motionless with a constant intraocular pressure (IOP). The latter is especially critical during open-eye operations such as corneal transplantation or open-sky vitrectomy procedures when the risk of vitreous loss or expulsive choroidal hemorrhage is present. Moreover, it is important to appreciate that drugs administered to produce pupillary dilation or to reduce IOP may be absorbed systemically from the conjunctiva or (predominantly) from the nasal mucosa after drainage through the nasolacrimal duct. Such systemic absorption has important anesthetic implications. Nasolacrimal duct occlusion is an effective way to minimize systemic absorption, and this maneuver is important in small children who are extremely vulnerable to the toxic effects of such drugs as scopolamine or phenylephrine. Additionally, topical administration of these drugs should be avoided in eyes with open conjunctival wounds. Examples of potentially worrisome topical ocular drugs include cyclopentolate, echothiophate iodide, epinephrine, and timolol. Intraocular drugs also have important anesthetic implications. Nitrous oxide, for example, should not be used concomitantly in eyes that receive intraocular air or gas. To avoid significant changes in the volume of the injected bubble and associated dangerous changes in IOP, nitrous oxide should be discontinued 15 to 20 minutes before an intravitreous air or gas injection administered to tamponade a detached retina [21]. Furthermore, if a patient requires a repeat operation after intravitreous gas injection, the typical recommendation is that nitrous oxide should be omitted for 5 days after an air injection and for 10 days after a sulfur hexafluoride injection [22]. In
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cases where perfluoropropane has been injected, the nitrous oxide proscription should be in effect for longer than 30 days [23]. It is important to point out, however, that resorption time is not uniform or always predictable. For example, reports have appeared where a 19-year-old woman with type 1 diabetes injected with sulfur hexafluoride 25 days before subsequent surgery and a 37-year-old male with insulindependent diabetes injected with perfluoropropane gas 41 days before subsequent surgery were given nitrous oxide and developed central retinal artery occlusion and permanent blindness in the affected eye [24]. Because the pressure in retinal arterial vessels is lower in patients with diabetes, the elderly, and those with atherosclerosis, these patients are probably at higher risk for this devastating complication [25 – 29]. The international distributor of medical-grade gases, in cooperation with the American distributors and the US Food and Drug Administration (FDA), has begun to provide hospital band-type warning bracelets for patients who receive intraocular gas injection to alert other health professionals to the presence of the bubble and the need to avoid nitrous oxide administration. Because many eye surgery patients are elderly, they may have arthritic involvement of the cervical spine and the temporomandibular joint, which can make laryngoscopy difficult or, occasionally, impossible. Thus, equipment designed to facilitate intubation, such as gum elastic bougies, fiberoptic endoscopes, laryngeal mask airways, and a variety of laryngoscope blades and endotracheal tube sizes, should be readily available. The logistic exigencies of ophthalmic anesthesia are such that the anesthesiologist is positioned remote from the patient’s airway. It is, therefore, essential to meticulously secure the endotracheal tube. Additionally, the anesthetic tubing should be positioned so that torsional strains do not occur that might inadvertently occlude the endotracheal tube by causing it to kink or twist. All connections should be firmly secured because movement of the head by the surgeon might dislodge a weak connection. Finally, the eye that is not undergoing surgery should be taped shut and a shield applied to prevent injury. Many ophthalmologists request that the patient’s nares be packed with gauze to prevent nasal secretions from contaminating the eye during surgery. The laryngeal mask airway (LMA) has gained great popularity in the past 15 years. Having the advantage of being easy to position without laryngoscopy or muscle relaxants, the LMA does not produce the same marked degree of vasopressor and oculotensive reflexes associated with endotracheal intubation and is less apt to cause dental damage. Initially, it
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was thought that the LMA was less likely to produce a sore throat [30,31], but more recent prospective investigations question the purported advantage of the LMA versus an endotracheal tube in regard to minor laryngopharyngeal morbidity [32]. The classic LMA does not protect against aspiraton, however, and many geriatric patients have an incompetent esophagogastric junction that may allow reflux of gastric contents. Moreover, many patients with diabetes mellitus also have gastroparesis. These patients, and others with significant risk factors for aspiration, are managed prudently by intubation with a cuffed endotracheal tube to protect the lungs. A wide assortment of anesthetic agents can be administered safely and effectively in ophthalmic surgery. Virtually any of the inhalation agents can be administered after intravenous induction with a barbiturate or propofol. Similarly, a total intravenous anesthetic technique with a propofol infusion and other intravenous medications as needed can be administered. Because it is consistently associated with less postoperative nausea and vomiting than other agents [33 – 35], propofol is an excellent drug for patients undergoing ophthalmic surgery. Recovery from propofol is rapid and typically associated with a sense of well-being [36], even euphoria, making it a very suitable drug for ambulatory surgery. Moreover, propofol attenuates the hypertensive response to intubation and reduces IOP, similar to most intravenous anesthetic drugs commonly used during eye surgery, such as narcotics and other sedative-hypnotics [37,38]. Propofol, however, frequently produces discomfort or pain when injected into small veins. This complication can be minimized or prevented by preadministration of, or admixing with, 20 mg lidocaine. Moreover, new formulations of propofol designed to be less irritating to veins are currently being evaluated. In patients with significant coronary artery or other types of heart disease, the cardiodepressant effects of barbiturates or propofol are unwelcome. Induction with intravenous etomidate may be more benign in terms of the cardiovascular system but, unfortunately, can trigger postoperative nausea and vomiting and possibly also result in short-term depression of adrenocortical function. The selection of the optimal muscle relaxant to facilitate intubation is made after assessing the patient’s airway and the probable degree of difficulty of intubation, the presence of symptomatic reflux, the hemodynamic consequences of the neuromuscular blocking agent, and the estimated duration of the surgery. Satisfactory control of arterial blood pressure is always important, but it has special implications for retinal perfusion in patients having vitreoretinal sur-
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gery. If the patient’s mean arterial pressure is markedly reduced, the retinal perfusion may be inadequate and compromise the visual outcome of surgery. Alternatively, marked elevation of retinal arteriole pressure can be dangerous. Therefore, it behooves the anesthesiologist to be cognizant of the patient’s normal blood pressure and endeavor to maintain hemodynamic variables within an acceptable range for each individual patient. Various inhalation agents are available for intraoperative maintenance of anesthesia, including isoflurane, desflurane, and sevoflurane. All these agents lower IOP in a dose-dependent fashion, provided oxygenation and ventilation are satisfactorily maintained. Desflurane and sevoflurane, the two newest inhalation agents in widespread use, have lower blood-gas solubilities than all previously used potent inhaled agents. In theory, this solubility advantage allows greater control of anesthetic depth and more rapid recovery from general anesthesia. Desflurane has the lowest blood-gas solubility of all volatile agents and is associated with the fastest immediate awakening after surgery. Data indicate that desflurane resists in vivo degradation more than any other potent halogenated agent. The limited biodegradation that does occur appears to be approximately one tenth that of isoflurane, the least degraded of the other available halogenated agents. This lack of significant biotransformation suggests relative safety in terms of potential toxicity from metabolites. The cardiovascular effects of desflurane involve the direct effects of the agent, and a transient response linked to sympathetic nervous system activation. The direct hemodynamic effects of desflurane are quite similar to those of isoflurane, including a reduction in peripheral vascular resistance and blood pressure. Prolongation of the QTc interval has been reported with many anesthetic drugs including isoflurane, sevoflurane, and desflurane [39]. However, the transient sympathetic activation seen with desflurane administered in combination with nitrous oxide is not encountered with isoflurane, but had been reported with diethyl ether. Although the precise mechanism responsible for this response has not been definitively established, beta-adrenergic activation leading to major increases in blood pressure and heart rate through increased plasma epinephrine and norepinephrine levels has been postulated [40]. The extent of sympathetic activation is related, at least partially, to the absolute concentration of desflurane as well as to the rapidity of increase in the concentration of desflurane. Thus, an extremely rapid progression to high concentrations of desflurane triggers more dramatic sympathetic stimulation [40,41]. This sympa-
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thetic response can be attenuated by pretreatment with clonidine or intravenous fentanyl, esmolol, or propofol. Nonetheless, many clinicians think it is best to avoid desflurane in patients with a history of myocardial ischemia, or else to administer only relatively low concentrations of the agent and to increase the concentration gradually as indicated. Many of the physicochemical characteristics and pharmacologic properties of sevoflurane suggest that it is well suited for use in ophthalmic surgery. Compared with desflurane, sevoflurane has the advantage of being nonirritating to the airway. Inhalational induction of anesthesia with sevoflurane is accomplished smoothly and quickly, making it the agent of choice in young children who are afraid of needles and would, therefore, prefer to avoid an intravenous induction. Coughing, laryngospasm, and breathholding are lesser problems than they are with isoflurane or desflurane, even with so-called single breath inductions. Additionally, sevoflurane, unlike desflurane, has a cardiovascular profile that is quite predictable, and it does not activate the sympathetic nervous system [42]. The incidence of bradycardia and arrhythmias during inhalation induction in children is also much lower than with halothane [43]. Occasionally, the occurrence of opisthotonic and seizurelike activity with sevoflurane has been noted [44 – 46]. The seizurelike activity has been reported at variable sevoflurane concentrations and during induction, maintenance, and recovery. The phenomenon has been observed in adults as well as children. It is reassuring that all of the patients who demonstrated the seizurelike activity recovered without incident. Nonetheless, clinicians should be aware of this problem, which is listed in the drug insert provided by Abbott Pharmaceuticals [47]. Sevoflurane is unstable under in vitro and in vivo conditions, producing compound A and fluoride. Compound A has been shown to be nephrotoxic in rats, and high fluoride concentrations can be nephrotoxic in humans. However, despite extensive clinical investigations, multiple studies have not demonstrated any clinically significant renal or hepatic dysfunction in humans, even at very low gas flows [48,49]. Indeed, sevoflurane has been administered to more than 120 million patients worldwide with an impressive safety record. It appears that the likelihood of long-term toxicity in humans from sevoflurane administered according to the guidelines in the package insert is extremely low, even when given for prolonged procedures. Similar to desflurane, awakening and emergence from sevoflurane are rapid and complete. However, emergence excitement or agitation is not uncommon with desflurane and
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sevoflurane. The times until discharge for ambulatory patients in whom desflurane or sevoflurane was used are comparable with more soluble agents like isoflurane or enflurane [50]. Whether this finding reflects a true lack of improvement in recovery time, or merely inertia in the ambulatory center system, remains to be determined. Regardless of which agent is selected, it should be carefully titrated and, because akinesia is important for delicate ocular surgery, administration of a nondepolarizing muscle relaxant is advised, in conjunction with peripheral nerve monitoring to ensure a twitch height suppression of 90% to 95% during open-eye surgery. Ventilation should be controlled and continuously monitored by end-tidal CO2 determination to avoid hypercarbia and its ocular hypertensive effect as well as to detect inadvertent disconnection of the endotracheal tube from the anesthesia circuit, a dangerous event that can be obscured by the surgical drapes. Continuous monitoring of arterial oxygen saturation by pulse oximetry is also essential. After completion of surgery, any residual neuromuscular block should be reversed. Intravenous lidocaine can be administered a few minutes before extubation to prevent or attenuate periextubation coughing. Depending on such factors as the patient’s airway anatomy, NPO (nil per os) status, and history of reflux, either awake or deep extubation may be selected. In skilled hands, either technique is satisfactory for patients who were fasting, who have normal airway anatomy, and who have no risk factors for reflux.
Postoperative nausea and vomiting: prevention and therapy Postoperative nausea and vomiting (PONV) account for a major proportion of unanticipated admissions to the hospital after intended ambulatory surgery, especially in children. Fortunately, after age 50 the incidence of PONV declines by more than 10% during each subsequent decade. The incidence of PONV is higher with narcotic-based anesthesia and with volatile agents. The incidence is lowest with a total intravenous anesthetic technique using propofol. The emetic effect of anesthetics are modulated in the chemoreceptor trigger zone, where serotonergic, histaminic, muscarinic, and dopaminergic receptors are found [34]. Input also comes from vagal and other stimulation directly to the emetic center. Although pharmacologic agents that act on the chemoreceptor trigger zone are well represented in our antiemetic armamentarium, the neurokinin1
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(NK1) antagonists are the only available antiemetics that act on the vomit center. Traditional antiemetics include benzamides such as metoclopramide, butyrophenones such as droperidol, and phenothiazines such as prochlorperazine. These three classes of drugs antagonize dopamine receptors. Scopolamine and atropine are anticholinergics that antagonize muscarinic receptors. Dimenhydrinate, diphenhydramine, and hydroxyzine antagonize histamine receptors. Other useful antiemetics include steroids such as dexamethasone and assorted agents such as ephedrine and propofol. Newer drugs include the 5-HT3 serotonergic receptor antagonists, such as ondansetron, tropisetron, and granisetron, which are expensive but generally effective. The 5-HT3 blockers are attractive because of the paucity of side effects associated with their use. Unlike many other antiemetics, which can cause drowsiness, dry mouth, or extrapyramidal symptoms, the 5-HT3 antagonists have a clean profile, except for headache and mild effects on liver function tests. However, similar to droperidol, some of the drugs in this category can prolong the QT interval. Unlike droperidol, however, these drugs have not been subject to a black box warning from the FDA. Our knowledge concerning the pathophysiology and management of PONV has grown impressively in the past 15 years. We now believe, for example, that universal PONV prophylaxis is not cost-effective. Rather, prophylactic treatment should be directed toward those at increased risk for the complication. Apfel and colleagues have developed a simplified risk score that identifies four major risk factors: female gender, nonsmoking status, history of PONV, and opioid use [51]. In this investigation of inpatients receiving balanced inhaled anesthesia the incidence of PONV with none, one, two, three, or all four risk factors was approximately 10%, 20%, 40%, 60%, and 80%, respectively. Apfel and colleagues claimed that, for inpatients, the type of surgery was not an independent risk factor. Sinclair and colleagues, however, reported that certain ophthalmic procedures, such as strabismus correction, were predictive of an increased risk of PONV [52]. Recently, guidelines have been developed to provide a comprehensive, evidence-based reference tool for the management of patients at moderate or high risk for PONV [53]. Double and triple antiemetic combinations (each with a different mechanism of action) are recommended prophylactically for patients at high risk for PONV. All prophylaxis in children at moderate or high risk for postoperative vomiting should be with combination therapy using a 5-HT3 antagonist and a second drug from a different category. Antiemetic rescue therapy should be admin-
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istered to patients who have an emetic episode after surgery. If PONV occurs within 6 hours after surgery, patients should not receive a repeat dose of the prophylactic antiemetic(s). Rather, a drug from another class should be given.
Guidelines for diabetic patients undergoing general anesthesia Estimates reflect that as many as 15 million people in the United States have diabetes mellitus. Ninety percent of diabetic individuals have noninsulin-dependent, or type 2, diabetes mellitus, and 10% have insulin-dependent, or type 1, diabetes mellitus requiring exogenous insulin to prevent ketoacidosis. Diabetes affects virtually every tissue of the body and shortens average life expectancy by up to 15 years. The emotional toll and financial costs of diabetes and its complications are an estimated $132 billion annually. This estimate reflects both direct health care costs as well as lost productivity. More than one of every four Medicare dollars is spent on people with diabetes. It is sobering to realize that diabetes and its complications rank as the third leading cause of death by disease in the United States. Given the pandemic of obesity currently afflicting our country, one can anticipate that the number of diabetic individuals will continue to climb. End-organ disease The renal, neurologic, cardiovascular, and ophthalmic complications of diabetes mellitus have been well described. Both the presence and extent of endorgan disease in an individual diabetic patient and the metabolic perturbations induced by the stress of anesthesia and surgery must be thoroughly comprehended if one is to formulate a rational and effective perioperative management plan. Cardiovascular abnormalities include coronary artery disease, hypertension, cardiac autonomic neuropathy, and impaired ventricular function. Occasionally, unexpected sudden death may occur in association with autonomic nervous system dysfunction. Because atherosclerosis and microangiopathy occur at an earlier age in diabetic patients compared with nondiabetic individuals, a diabetic patient’s physiological age is much older than the stated chronologic age. Thus, coronary artery disease is common in long-standing type 1 diabetes, even at age 25 or 30 years. Myocardial infarction is 5 to 10 times more common in type 1 and type 2 diabetic individuals with end-organ disease than in the general
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population. Because diabetic adults are considered at high risk for perioperative myocardial ischemia, a baseline ECG should be obtained on all adult diabetic individuals. Anesthetic management is then adjusted appropriately to the results of preoperative assessment and intraoperative hemodynamic performance. Hypertension is extremely common in diabetic patients, and may be a marker for possible coronary artery disease. The presence of left ventricular hypertrophy suggests impaired autoregulation of coronary perfusion, rendering these patients vulnerable to ischemia with even a moderate reduction in blood pressure. Satisfactory control of blood pressure before surgery should foster stable intraoperative and postoperative hemodynamic function. However, perioperative hemodynamic instability may occur owing to altered sympathetic tone, reduced baroreceptor function, relative hypovolemia associated with chronic vasoconstriction, and anesthetic interactions with some antihypertensive medications. Because of the diabetic patient’s limited ability to autoregulate coronary perfusion, the anesthesiologist should attempt to maintain blood pressure within ±20% of baseline values. The presence of orthostatic hypotension, an elevated resting heart rate, or a reduction or absence of a normal beat-to-beat variation of heart rate during deep breathing suggests the possibility that the patient may have cardiac autonomic neuropathy. This condition manifests as an impaired cardiovascular stress response and may be accompanied by painless myocardial ischemia. Additionally, diabetic patients with autonomic neuropathy may have abnormal hypoxic drive mechanisms centrally or peripherally and hence are at greater risk for sudden, unexpected cardiac and respiratory arrest in the setting of hypoxia [54,55]. Those with painless myocardial ischemia may also have occult left ventricular dysfunction, which can result in CHF if the patient is given a volume overload perioperatively. Impaired gastric emptying is also a consequence of autonomic dysfunction, and can increase the risk of perioperative aspiration and PONV. Administration of IV metoclopramide to facilitate gastric emptying may be helpful. Diabetic renal disease, including renal papillary necrosis and glomerulosclerosis, renders the diabetic patient susceptible to perioperative acute renal failure. Additionally, a diabetic patient is at greater risk for urosepsis, which may contribute to systemic sepsis and acute renal failure. Fixation of the atlanto-occipital joint with limitation of head extension may make endotracheal intubation difficult [56]. ‘‘Stiff joint syndrome’’ typi-
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cally occurs in type 1 diabetic patients and is associated with short stature, small joint contractures, and tight, waxy skin. The etiology is thought to be abnormal collagen cross-linking by nonenzymatic glycosylation, which may occur in up to 25% of juvenile diabetic individuals [57]. This abnormal collagen glycosylation may also lead to possible atlanto-occipital dislocation. A defective palm print or ‘‘prayer sign’’ in these patients (owing to an inability to approximate the interphalangeal joints of the hand) is often associated with difficult intubation and, therefore, should be assessed preoperatively so that appropriate airway management can be planned, enabling the necessary equipment to be immediately available. Clearly, meticulous attention must be paid to a thorough preoperative assessment and optimization of the patient’s medical condition, as well as careful titration of the drugs and fluids administered perioperatively. Attention must also be paid to proper positioning and padding intraoperatively, because the diabetic patients are especially vulnerable to pressure ischemia of nerves and vasculature. A retrospective study assessed perioperative risk of nonocular surgery in diabetic patients [58]. Overall, 15% of patients had significant complications, and there were major differences in outcome depending on the presence or absence of end-organ damage. Patients with serious cardiac disease were more prone to major perioperative cardiac complications. Noncardiac complications, including infection, renal insufficiency, and cerebral ischemia, occurred in 24% of patients with end-organ disease (retinopathy, neuropathy, or nephropathy), in 29% of those with CHF, and in 35% of those with peripheral vascular disease. In patients without preexisting conditions, noncardiac complications (6%) and cardiac complications (4%) were rare. Moreover, the type of anesthetic selected was not predictive of risk of complications. The study emphatically underscored, however, that increased morbidity and mortality occur in diabetic patients with cardiac and end-organ disease. Control of glucose Despite the known advantages of ‘‘tight’’ or near euglycemic control in the chronic diabetic state, the concept of rigidly tight control is controversial in the perioperative period. Aggressive attempts to achieve euglycemia may result in dangerous episodes of hypoglycemia that may be masked by anesthesia and sedation. Therefore, the perioperative blood sugar level should be maintained in the range of approximately 100 to 180 mg/dL. Patients with insulin-
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dependent diabetes mellitus (type 1) tend to be more ‘‘brittle’’ than those with type 2 diabetes, and surgery for type 1 patients should be scheduled as early in the day as possible. Several regimens for insulin and substrate infusions have been advocated, but one of two protocols is generally followed. All treatment options require frequent measurement of blood glucose and treatment of hypoglycemia and hyperglycemia as needed. The blood glucose level is determined preoperatively, and an intravenous infusion of dextrose 5% (D5) and 0.25 normal saline is begun. One half of the usual neutral protamine Hagedorn (NPH) insulin dosage is administered, provided the blood sugar level is above 150 mg/dL. Blood glucose levels are monitored frequently (usually hourly) during the intraoperative period. Regular insulin doses of 0.1 unit/kg are given when the plasma glucose level exceeds 200 mg/dL. In contrast, if the blood glucose level is below 100 mg/dL, more intravenous dextrose is administered. Alternatively, a simultaneous insulin and glucose infusion may be given to a type 1 patient after a preoperative blood sugar level has been established. The infusion contains 1 to 2 units of insulin per 100 mL of 5% dextrose in water, and the infusion rate allows for 0.2 to 0.4 units of insulin per gram of glucose. Blood glucose levels are maintained in the desired range by titrating the infusion rate. Type 2 diabetic patients taking daily insulin are managed in a manner analogous to that for type 1 diabetic individuals. Those patients on oral hypoglycemics should refrain from taking the hypoglycemic agent on the day of surgery. After the fasting blood sugar level has been established an appropriate intravenous infusion is initiated. A postoperative blood sugar level is determined, with therapeutic and dietary instructions provided accordingly. An ophthalmic patient is usually able to tolerate oral intake within a relatively brief period after surgery. When oral intake is adequate, the patient may resume his or her usual diabetic regimen.
Considerations for select high-risk patients Marfan syndrome Marfan syndrome is a disorder of connective tissue, involving primarily the cardiovascular, skeletal, and ocular systems. However, the skin, fascia, lungs, skeletal muscle, and adipose tissue may also be affected. The etiology is a mutation in FBNI, the gene that encodes fibrillin-1, a major component of extracellular microfibrils, which are the major compo-
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nents of elastic fibers that anchor the dermis, epidermis, and ocular zonules [59]. Connective tissue in this disorder has decreased tensile strength and elasticity. Marfan syndrome is inherited as an autosomal dominant trait with variable expression. Ocular manifestations of the syndrome include severe myopia, spontaneous retinal detachment, lens displacement, and glaucoma. Cardiovascular manifestations include dilation of the ascending aorta and aortic insufficiency. The loss of elastic fibers in the media may also account for dilation of the pulmonary artery and mitral insufficiency resulting from extended chordae tendinae. Myocardial ischemia owing to medial necrosis of coronary arterioles as well as dysrhythmias and conduction disturbances have been well documented. Heart failure and dissecting aortic aneurysms or aortic rupture are not uncommon. The patients are tall, with long, thin extremities and fingers (arachnodactyly). Joint ligaments are loose, resulting in frequent dislocations of the mandible and hip. Possible cervical spine laxity can also occur. Kyphoscoliosis and pectus excavatum can contribute to restrictive pulmonary disease. Lung cysts have also been described, causing an increased risk of pneumothorax. A narrow, high-arched palate is commonly found. The early manifestations of Marfan syndrome may be subtle, and therefore the diagnosis may not yet have been made when the patient comes for initial surgery. The anesthesiologist, however, should have a high index of suspicion when a tall young patient with a heart murmur presents for repair of a spontaneously detached retina. These young patients should have a chest radiograph as well as an electrocardiogram and echocardiogram before surgery. Antibiotics for subacute bacterial endocarditis prophylaxis should be considered, as well as b-blockade to mitigate increases in myocardial contractility and aortic wall tension (dP/dT). The anesthesiologist should be prepared for a potentially difficult intubation. Laryngoscopy should be carefully performed to circumvent tissue damage and, especially, to avoid hypertension with its attendant risk of aortic dissection. The patient should be carefully positioned to avoid cervical spine or other joint injuries, including dislocations. The dangers of hypertension in these patients are well known. Clearly, the presence of significant aortic insufficiency warrants that the blood pressure (especially the diastolic pressure) be high enough to provide adequate coronary blood flow but should not be so high as to risk dissection of the aorta. Maintenance of the patient’s normal blood pressure is typically a good plan. No single intraoperative anesthetic agent
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or technique has demonstrated superiority. If pulmonary cysts are present, however, positive pressure ventilation may lead to pneumothorax [60]. At extubation, one should take care to avoid sudden increases in blood pressure or heart rate. Adequate postoperative pain management is vitally important to avoid the detrimental effects of hypertension and tachycardia. Myotonic dystrophy Myotonic dystrophy, also known as myotonia dystrophica or Steinert’s disease, is a genetically transmitted autosomal dominant disease with variable and unpredictable penetrance and phenotypic presentation. Myotonia denotes a characteristic persistent contracture after cessation of voluntary contraction or electrical or percussive stimulation. This inability of skeletal muscle to relax is diagnostic. Electromyography is corroborative and pathognomonic, showing continuous, low-voltage activity with high-voltage, fibrillation-like potential bursts. Myotonia can be initiated or exacerbated by exercise or cold temperature and a host of other conditions and drugs. The most common form of myotonic dystrophy is localized to chromosome 19, locus q12.3, the gene that codes for serine/threonine kinase. An abnormally long trinucleotide repeat is thought to lead to the disease. Moreover, within a given patient there is mosaicism in the aberrant repeat sequences in different tissues. A defect in sodium and chloride channel function produces electrical instability of the muscle membrane and self-sustaining runs of depolarization. Additionally, abnormal calcium metabolism may be involved. In contrast to most myopathies, the distal muscles are more affected than proximal muscles. Although patients can present at any age from infancy to late life, typically myotonic dystrophy manifests in the second or third decade. Myotonia is the predominant manifestation early in the disease, but as the condition progresses, muscle weakness and atrophy become more apparent. Facial muscles (orbicularis oculi and oris, masseter, and so forth) frequently develop marked atrophy, producing a characteristic expressionless facial appearance sometimes described as ‘‘hatchet face.’’ Multiple organ systems are affected. Cardiac manifestations, which are often noted before the appearance of other clinical symptoms, consist of atrial or ventricular tachyarrhythmias, conduction abnormalities including varying degrees of heart block, and, less frequently, impaired ventricular function [61,62]. Mitral valve prolapse is said to occur in approximately 15% of myotonic patients [62]. Respiratory involvement consists of a restrictive pattern of dis-
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ease, with respiratory and sternocleidomastoid muscle weakness leading to reduced vital capacity. Patients typically develop a weak cough, dyspnea, and frequent episodes of pneumonia. Alveolar hypoventilation is caused by either pulmonary or central nervous system dysfunction. Chronic hypoxemia may result in cor pulmonale. Assorted other stigmata include presenile cataracts, ptosis, strabismus, and premature frontal balding. Endocrine dysfunction leads to adrenal [63], thyroid, pancreatic [64], and gonadal insufficiency. Central nervous system manifestations include mental retardation, central sleep apnea, and hypersomnolence, as well as psychiatric aberrations. Delayed esophageal and gastric emptying [65], in combination with compromised ability to swallow [66], can predispose patients to pulmonary aspiration. Moreover, uterine atony can retard labor and increase the likelihood of retained placenta. Treatment of myotonic dystrophy can be undertaken with membrane-stabilizing medications, such as phenytoin, quinine sulfate, and procainamide. Although phenytoin has not been implicated in the exacerbation of cardiac conduction abnormalities, quinine and procainamide may prolong the P-R interval. A cardiac pacemaker should be inserted in patients with significant conduction defects, even if they appear to be asymptomatic. Patients with myotonic dystrophy offer multiple challenges to the anesthesiologist because they are at high risk for serious perioperative respiratory and cardiac complications. (Apparently, this condition can also complicate surgical results. Three case reports, for example, describe seemingly uneventful cataract surgery that was complicated postoperatively by recurrent opacifications and intraocular fibrosis [67].) It is vital to appreciate that a small number of patients with this condition may be presymptomatic and undiagnosed. Indeed, although rare, there are reports of patients with myotonic dystrophy in whom the diagnosis was made only after an episode of prolonged apnea occurred following general anesthesia. Typically, however, the patient’s diagnosis is known, and that individual suffers from a host of associated conditions including restrictive lung disease, conduction defects, cardiomyopathy, hypothyroidism, diabetes, dysphagia, and delayed gastric emptying. Patients with myotonic dystrophy have altered responses to a vast spectrum of anesthetic drugs. They are frequently extremely sensitive to even small doses of opioids, sedatives, and inhalation agents, all of which may trigger prolonged apnea. Succinylcholine is considered relatively contraindicated because it can precipitate intense myotonic contractions. Moreover, trismus can abolish the ability to open the mouth for
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oral intubation. Myotonic contraction of respiratory, chest wall, or laryngeal muscles can render ventilation difficult or impossible. Additionally, hypothermia, shivering, struggling during an inhalation induction, application of a tourniquet, performing a painful needle stick for intravenous induction, surgical manipulation, and using electrocautery or a peripheral nerve stimulator can all trigger myotonic contractions. Other drugs that act at the motor end plate, such as neostigmine and physostigmine, can exacerbate myotonia. Regional anesthesia can be administered but does not reliably prevent myotonic contractions, which do respond to intramuscular injection of procaine or intravenous administration of 300 to 600 mg quinine hydrochloride. Even nondepolarizing muscle relaxants do not consistently prevent myotonic contractions. Because reversal agents can theoretically trigger myotonic contractions, the use of relatively short-acting nondepolarizing drugs, such as mivacurium, is recommended. Small doses of meperidine may be judiciously administered to prevent the shivering commonly associated with hypothermia and the use of volatile anesthetics. Short-acting opioids, such as alfentanil or remifentanil, are recommended to avoid prolonged postoperative respiratory depression and obtundation. Obviously, temperature monitoring is important, as is the use of warmed IV fluids, warmed humidified inhaled gases, and use of a warming blanket. Moreover, aspiration prophylaxis is probably prudent. Aggressive pulmonary hygiene with physical therapy, incentive spirometry, and vigilant postoperative monitoring are warranted. In the past, there was speculation about an association between myotonic dystrophy and malignant hyperthermia. This possible link has not been confirmed, however. Interestingly, both conditions map to chromosome 19, but have different loci. The literature suggests that there is no association between the type of anesthesia administered and any postoperative complications. Risk of pulmonary complications appears to be greatest in those with severe disability and those having upper abdominal surgery. Because a variety of approaches have been used successfully, there is no single best method. The risks and benefits should be assessed individually to tailor an appropriate anesthetic plan.
Summary Skillful anesthetic management is integral to optimal outcomes after ophthalmic surgery. Although
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the majority of ophthalmic operations in the United States are performed with local anesthetic techniques, nonetheless general anesthesia may be either necessary or advisable in several challenging circumstances. Ophthalmic patients are often at the extremes of age, and not uncommonly have extensive associated systemic or metabolic diseases. Because the complications of ophthalmic anesthesia can be vision threatening or life threatening, it is imperative that the ophthalmologist and the anesthesiologist understand the complex and dynamic interaction among patient disease(s), anesthetic agents, ophthalmic drugs, and surgical manipulation. Effective communication and planning among all involved are essential to safe and efficient perioperative care.
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