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© 2008 BC Decker Inc 1 BASIC SURGICAL AND PERIOPERATIVE CONSIDERATIONS ACS Surgery: Principles and Practice 3 PERIOPERATIVE CONSIDERATIONS FOR ANESTHESIA — 1 3 PERIOPERATIVE CONSIDERATIONS FOR ANESTHESIA Steven B. Backman, MDCM, PhD, FRCPC, Richard M. Bondy, MDCM, Alain Deschamps, MD, PhD, Anne Moore, MD, and Thomas Schricker, MD, PhD Advancements in modern surgical care are complemented by alterations in anesthetic management to provide maximum patient benefit. During the last two decades, anesthesia practice has changed enormously—with the proliferation of airway devices; the routine employment of patient-controlled analgesia; the wider popularity of regional anesthesia, including thoracic epidural anesthesia and peripheral nerve blocks; the development of computer-controlled devices for infusing short-acting drugs; the discovery and use of quickly reversible inhalational drugs, opiates, and muscle relaxants; the availability of online monitoring of central nervous system (CNS) function; and the increased application of transesophageal echocardiography, to name but a few examples. Our aim in this chapter is to offer surgeons a current perspective on perioperative considerations for anesthesia to facilitate dialogue between the surgeon and the anesthesiologist and thereby ensure optimum care for our patients. The primary focus is on the adult patient: the special issues concerning pediatric anesthesia are beyond the scope of our review. In addition, the ensuing discussion is necessarily selective; more comprehensive discussions may be found elsewhere.1,2 Perioperative Patient Management Preoperative medical evaluation is an essential component of preoperative assessment for anesthesia. Of particular importance to the anesthesiologist is any history of personal or family problems with anesthesia. Information should be sought concerning difficulty with airway management or intubation, drug allergy, delayed awakening, significant postoperative nausea and vomiting (PONV), unexpected hospital or intensive care unit (ICU) admission, and post–dural puncture headache (PDPH). Previous anesthetic records may be requested. The airway must be carefully examined to identify patients at risk for difficult ventilation or intubation [see Special Scenarios, Difficult Airway, below], with particular attention paid to teeth, caps, crowns, dentures, and bridges. Patients must be informed about the risk of trauma associated with intubation and airway management. Anesthetic options [see Choice of Anesthesia, below] should be discussed, including the likelihood of postoperative ventilation and admission to the hospital or ICU. When relevant, the possibility of blood product administration should be raised [see 1:4 Bleeding and Transfusion], and the patient’s acceptance or refusal of transfusion should be carefully documented. Postoperative pain management [see 1:6 Postoperative Pain] should be addressed, particularly when a major procedure is planned. The risks associated with general or regional anesthesia (see below) should be discussed in an informative and reassuring manner; a well-conducted preoperative anesthesia interview plays an important role in alleviating anxiety. The medications the patient is taking can have a substantial impact on anesthetic management. Generally, patients should continue to take their regular medication up to the time of the operation. It is especially important not to abruptly discontinue medications that may result in withdrawal or rebound phenomena (e.g., beta blockers, alpha antagonists, barbiturates, and opioids). With some medications (e.g., oral hypoglycemics, insulin, and corticosteroids), perioperative dosage adjustments may be necessary [see 8:10 Endocrine Problems]. Angiotensin-converting enzyme inhibitors have been associated with intraoperative hypotension and may be withheld at the discretion of the anesthesiologist.3 Drugs that should be discontinued preoperatively include monoamine oxidase inhibitors (MAOIs) and oral anticoagulants [see Table 1]. Many surgical patients are taking antiplatelet drugs. Careful consideration should be given to the withdrawal of these agents in the perioperative period [see Table 1] because of the possibility that discontinuance may lead to an acute coronary syndrome. Patients with recently placed coronary artery drug-eluting stents (< 1 year) may be at particular risk, so elective surgery should be postponed.4 If surgery is necessary, and patients are deemed to be at increased risk for medication-related bleeding during surgery, the longer-acting agents (e.g., aspirin, clopidogrel, and ticlopidine) can be replaced with nonsteroidal antiinflammatory drugs (NSAIDs) that have shorter half-lives. Typically, these shorter-acting drugs are given for 10 days, stopped on the day of surgery, and then restarted 6 hours after operation. Platelet transfusion can be considered if there is a very high potential for significant bleeding.5 The increasing use of herbal and alternative medicines has led to significant morbidity and mortality as a consequence of unexpected interactions with traditional drugs. Because many patients fail to mention such agents as part of their medication regimen during the preoperative assessment, it is advisable to question all patients directly about their use. Particular attention should be given to Chinese herbal teas, which include organic compounds and toxic contaminants that may produce renal fibrosis or failure, cholestasis, hepatitis, and thrombocytopenia. Specific recommendations exist for the discontinuance of many of these agents [see Table 1]. Prophylactic administration of perioperative beta blockers in patients with or at risk for atherosclerotic disease undergoing noncardiac surgery is controversial and merits specific DOI 10.2310/7800.S01C03 11/08 © 2008 BC Decker Inc 1 BASIC SURGICAL AND PERIOPERATIVE CONSIDERATIONS Type of Drug MAOIs Table 1 Recommendations for Preoperative Discontinuance of Drugs and Medicine68–81 Agent Pharmacologic Effects Adverse Effects Discontinuance Recommendations Isocarboxazid Irreversible inhibition of Phenelzine monoamine oxidase Pargyline with the resultant Tranylcypromine increase in serotonin, Selegiline norepinephrine, epinephrine, dopamine, and octamine neurotransmitters Warfarin Oral anticoagulants Antiplatelet agents Inhibition of vitamin K– dependent clotting factors II, VII, IX, X Potentiation of sympathomimetic Elective surgery: discontinue at least amines, possible hypertensive crisis 2 wk in advance; consider potential May prolong and intensify effects of for suicidal tendency—mental other CNS depressants health specialist should be involved Severe idiopathic hyperpyrexic Emergency surgery: avoid meperidine; reaction with meperidine and consider regional anesthesia possibly other narcotics Potential catastrophic interaction with tricyclic antidepressants, characterized by high fever and excessive cerebral excitation and hypertension Bleeding Elective surgery: discontinue 5–7 days in advance; replace with heparin if necessary Aspirin and NSAIDs Aspirin Fenoprofen Ibuprofen Sodium meclofenamate Tolmetin Indomethacin Ketoprofen Diflunisal Naproxen Sulindac Piroxicam Thienopyridines Ticlopidine Clopidogrel Inhibition of May increase intraoperative and thromboxane A2 postoperative bleeding but not 80% of platelets must be transfusion requirement inhibited for therapeutic Perioperative hemorrhagic complicaeffect tions increase with increasing Susceptibility to aspirin half-life of drug varies between patients Antiglycoprotein agents Eptifibatide Tirofiban Abciximab Competitive inhibition of GPIIb/IIIa receptors to prevent platelet aggregation Rapid onset of action Short half-lives Often combined with aspirin and/or heparin Used as an alternative anticancer agent This herbal agent should be considered as dangerous Used as an antitussive and demulcent agent Considered dangerous Used as a general healing agent Considered dangerous Noncatecholamine sympathomimetic agent with a1, b1, and b2 activity; both direct and indirect release of endogenous catecholamines Herbal Chaparral medicines Coltsfoot Comfrey Ephedra/ma huang (Ephedra sinica) 11/08 ACS Surgery: Principles and Practice 3 PERIOPERATIVE CONSIDERATIONS FOR ANESTHESIA — 2 Inhibition of platelet aggregation Inhibition of platelet ADP–induced amplification Primary hemostasis normalizes in 48 hr in healthy persons; platelet activity fully recovered in 8–10 days Patients on long-term aspirin therapy for coronary or cerebrovascular pathology should not discontinue drug in perioperative period unless hemorrhagic complications of procedure outweigh risk of acute thrombotic event Synergistic antithrombotic effect with Discontinue ticlopidine 2 wk in aspirin advance; discontinue clopidogrel 7–10 days in advance Patients with coronary artery stents may receive aspirin plus ticlopidine for prolonged period after angioplasty; stopping therapy considerably increases risk of coronary thrombosis; elective surgery should be delayed for 1–3 mo Discontinue at least 12 hr in advance Literature (mainly from cardiac Transfuse platelets only if needed to surgery) shows increased hemorcorrect clinically significant bleeding rhagic risk if surgery undertaken < 12 hr after discontinuance of abciximab Individual variability in recovery time of platelet function Hepatotoxicity As soon as possible Carcinogenic As soon as possible Hepatotoxicity, liver failure As soon as possible Dose-dependent increase in HR and Discontinue at least 24 hr in advance BP, with potential for serious cardiac and CNS complications Possible adverse drug reactions: MAOIs (life-threatening hypertension, hyperpyrexia, coma), oxytocin (hypertension), digoxin and volatile anesthetics (dysrhythmias), guanethedine (hypertension, tachycardia) © 2008 BC Decker Inc 1 BASIC SURGICAL AND PERIOPERATIVE CONSIDERATIONS Type of Agent Drug Herbal Echinacea medicines (Echinacea purpurea) Feverfew Garlic (Allium sativum) Germander Ginkgo (Ginkgo biloba) Ginger (Zingiber officinale) Ginseng (Panax ginseng) Goldenseal Kava (Piper methysticum) Licorice (Glycyrrhiza glabra) Lobelia Sassafras Saw palmetto St. John’s wort (Hypericum perforatum) Valerian (Valeriana officinalis) Vitamin E Yohimbe ACS Surgery: Principles and Practice 3 PERIOPERATIVE CONSIDERATIONS FOR ANESTHESIA — 3 Table 1 Continued Pharmacologic Effects Adverse Effects Immunostimulatory effect Hepatotoxicity Allergic potential May increase bleeding especially in patients already on anticlotting medications Irreversible doseIncreased bleeding may potentiate dependent inhibition of other platelet inhibitors platelet aggregation Choleretic, antiseptic Hepatotoxicity properties Used in weight control Considered dangerous Inhibition of plateletIncreased bleeding activating factor May potentiate other platelet inhibitors Modulation of neurotransmitter receptor activity Potent inhibitor of Increased bleeding thromboxane synthase May potentiate effects of other anticoagulants Inhibition of platelet Prolonged PT and PTT Hypoglycemia aggregation, possibly irreversibly Reduced anticoagulation effect of warfarin Antioxidant action Antihyperglycemic action Possible additive effect with other stimulants, with resultant “Steroid hormone”–like hypertension and tachycardia activity May worsen swelling and/or high BP Dose-dependent potentia- Potentiation of sedative anesthetics, including barbiturates and tion of GABAbenzodiazepines inhibitory neurotransPossible potentiation of ethanol mitter with sedative, effects anxiolytic, and antiepileptic effects Hypertension Hypokalemia Edema Contraindicated in chronic liver and renal insufficiency Used as an antinausea and Respiratory depression, tachycardia, mild expectorant hypotension, hallucinations, coma, Considered dangerous death Stimulant, antispasmodic Carcinogenic Considered dangerous May interfere with other hormone therapies Inhibits reuptake of Possible interaction with MAOIs serotonin, norepineEvidence for reduced activity of phrine, and dopamine cyclosporine, warfarin, calcium by neurons Increases channel blockers, lidocaine, metabolism of some midazolam, alfentanil, and NSAIDs P-450 isoforms Dose-dependent Possible potentiation of sedative modulation of GABA anesthetics, including barbiturates neurotransmitter and and benzodiazepines receptor function May increase bleeding, especially in patients taking anticlotting agents May affect thyroid function in otherwise healthy patients In doses greater than 400 IU per day, further increase in BP may be seen in already hypertensive patients Aphrodisiac, sexual Hypertension, tachycardia, paralysis, death stimulant Considered dangerous Discontinuance Recommendations Discontinue as far in advance as possible in any patient with hepatic dysfunction or surgery with possible hepatic blood flow compromise At least 7 days Discontinue at least 7 days in advance As soon as possible Discontinue at least 36 hr in advance Discontinue at least 36 hr in advance Discontinue at least 7 days in advance At least 7 days As soon as possible As soon as possible At least 7 days Discontinue on day of surgery; abrupt withdrawal in physically dependent patients may produce benzodiazepine-like withdrawal syndrome Discontinue at least 24 hr in advance As soon as possible ADP = adenosine diphosphate; BP = blood pressure; CNS = central nervous system; GABA = b-aminobutyric acid; GP = glycoprotein; HR = heart rate; MAOIs = monoamine oxidase inhibitors; NSAIDs = nonsteroidal antiinflammatory drugs; PT = prothrombin time; PTT = partial thromboplastin time. 11/08 © 2008 BC Decker Inc 1 BASIC SURGICAL AND PERIOPERATIVE CONSIDERATIONS consideration. Although a subgroup of patients may benefit from such treatment with respect to decreased cardiac morbidity, overall, an increased risk of death, stroke, and clinically significant hypotension and bradycardia has been reported.6 As such, it is anticipated that guidelines regarding the role for beta blockers in the perioperative setting will continue to evolve.7 Inpatient versus Outpatient Surgery An ever-increasing number of operations are performed on an ambulatory basis [see ECP:5 Patient Safety in Surgical Care: A Systems Approach]. Operations considered appropriate for an ambulatory setting are associated with minimal physiologic trespass, low anesthetic complexity, and uncomplicated recovery.8,9 The design of the ambulatory facility may impose limitations on the types of operations or patients that can be considered for ambulatory surgery. Such limitations may be secondary to availability of equipment, recovery room nursing expertise and access to consultants, and availability of ICU or hospital beds. Patients who are in class I or class II of the American Society of Anesthesiologists (ASA) physical status scale are ideally suited for ambulatory surgery; however, a subset of ASA class III patients may be at increased risk for prolonged recovery and hospital admission [see Table 2]. Premedication to produce anxiolysis, sedation, analgesia, amnesia, and reduction in PONV and aspiration may be considered for patients undergoing outpatient procedures, as it may for those undergoing inpatient procedures. Such premedication should not delay discharge. Fasting guidelines [see Table 3] and intraoperative monitoring standards for ambulatory surgery are identical to those for inpatient procedures [see Patient Monitoring, below]. A number of currently used anesthetics (e.g., propofol, sevoflurane, desflurane), narcotics (e.g., alfentanil, fentanyl, sufentanil, and remifentanil), and muscle relaxants (e.g., succinylcholine, atracurium, mivacurium, and rocuronium) demonstrate rapid recovery profiles. Nitrous oxide also has desirable pharmacokinetic properties, but it may be associated with increased PONV. Titration of anesthetics to indices of CNS activity (e.g., the bispectral index) may result in decreased drug dosages, faster recovery from anesthesia, and fewer complications.10,11 Multimodal analgesia (involving the use of local anesthetics, ketamine, alpha2-adrenergic agonists, beta blockers, acetaminophen, or NSAIDs) may reduce Table 2 Association between Preexisting Medical Conditions and Adverse Outcomes82 Medical Condition Congestive heart failure Hypertension Asthma Smoking Obesity Reflux 11/08 Associated Adverse Outcome 12% prolongation of postoperative stay Twofold increase in risk of intraoperative cardiovascular events Fivefold increase in risk of postoperative respiratory events Fourfold increase in risk of postoperative respiratory events Fourfold increase in risk of intraoperative and postoperative respiratory events Eightfold increase in risk of intubation-related adverse events ACS Surgery: Principles and Practice 3 PERIOPERATIVE CONSIDERATIONS FOR ANESTHESIA — 4 Table 3 Fasting Recommendations* to Reduce Risk of Pulmonary Aspiration83 Ingested Material Minimum Fasting Period† (hr) ‡ 2 4 6 6 8 Clear liquids Breast milk Infant formula Nonhuman milk§¤ Light meal|| *These recommendations apply to healthy patients undergoing elective procedures; they are not intended for women in labor. Following the guidelines does not guarantee complete gastric emptying. † These fasting periods apply to all ages. ‡ Examples of clear liquids include water, fruit juices without pulp, carbonated beverages, clear tea, and black coffee. § Because nonhuman milk is similar to solids in gastric emptying time, the amount ingested must be considered in determining the appropriate fasting period. || A light meal typically consists of toast and clear liquids. Meals that include fried or fatty foods or meat may prolong gastric emptying time. Both the amount and type of foods ingested must be considered in determining the appropriate fasting period. intraoperative and postoperative opioid requirements and accelerate patient discharge. Use of a laryngeal mask airway rather than an endotracheal tube is ideal in the outpatient setting because lower doses of induction agent are required to blunt the hypertension and tachycardia associated with its insertion; in addition, it is associated with a decreased incidence of sore throat and does not require muscle paralysis for insertion. On the other hand, a laryngeal mask airway may not protect against aspiration.12,13 The benefits of regional anesthesia [see Regional Anesthesia Techniques, below] may include decreases in the incidence of aspiration, nausea, dizziness, and disorientation. Spinal and epidural anesthesia may be associated with headache (dural puncture) and backache. Compared with spinal anesthesia, epidural anesthesia takes more time to perform, has a slower onset of action, and may not produce as profound a block; however, the duration of an epidural block can readily be extended intraoperatively or postoperatively if necessary. Care should be exercised in choosing a local anesthetic for neuraxial blockade: spinal lidocaine may be associated with a transient radicular irritation, and bupivacaine may be associated with prolonged motor block; narcotics may produce pruritus, urinary retention, nausea and vomiting, and respiratory depression. Various dosing regimens, including minidose spinal techniques, have been proposed as means of minimizing these side effects.14–17 Monitored anesthesia care [see Choice of Anesthesia, below] achieves minimal CNS depression, so the airway and spontaneous ventilation are maintained and the patient is able to respond to verbal commands. Meticulous attention to monitoring is required to guard against airway obstruction, arterial desaturation, and pulmonary aspiration. In the recovery room, the anesthetic plan is continued until discharge. Shorter-acting narcotics and NSAIDs are administered for pain relief, and any of several agents may be given for control of nausea and vomiting. Criteria for discharge from the recovery room have been established [see Table 4]. Recovery of normal muscle strength and sensation (including proprioception of the lower extremity, autonomic function, and ability to void) should be demonstrated after spinal or epidural anesthesia. Delays in discharge are usually the result © 2008 BC Decker Inc 1 BASIC SURGICAL AND PERIOPERATIVE CONSIDERATIONS Table 4 Postanesthetic Discharge Scoring System (PADSS)84 Category Vital signs Score* 2 1 ACS Surgery: Principles and Practice 3 PERIOPERATIVE CONSIDERATIONS FOR ANESTHESIA — 5 definitive surgical treatment must not be unduly delayed by attempts to “get a line.” Explanation 0 Within 20% of preoperative value Within 20 to 40% of preoperative value Within 40% of preoperative value Activity, mental status 2 1 0 Oriented and steady gait Oriented or steady gait Neither Pain, nausea, vomiting 2 1 0 Minimal Moderate Severe Surgical bleeding 2 1 0 Minimal Moderate Severe Intake/output 2 1 0 Oral fluid intake and voiding Oral fluid intake or voiding Neither *Total possible score is 10; patients scoring g9 are considered fit for discharge home. of pain, PONV, hypotension, dizziness, unsteady gait, or lack of an escort.18 Elective versus Emergency Surgery Surgical procedures performed on an emergency basis may range from relatively low priority (e.g., a previously cancelled case that was originally elective) to highly urgent (e.g., a case of impending airway obstruction). For trauma, specific evaluation and resuscitation sequences have been established to facilitate patient management [see 7:1 Initial Management of Life-Threatening Trauma]. The urgency of the situation dictates how much time can be allotted to preoperative patient assessment and optimization. When it is not possible to communicate with the patient, information obtained from family members and paramedics may be crucial. Information should be sought concerning allergies, current medications, significant past medical illnesses, nihil per os (NPO) status, personal or family problems with anesthesia, and recent ingestion of alcohol or drugs. Any factor that may complicate airway management should be noted (e.g., trauma to the face or the neck, a beard, a short and thick neck, obesity, or a full stomach). When appropriate, blood samples should be obtained as soon as possible for typing and cross-matching, as well as routine blood chemistry, complete blood count, and toxin screen. Arrangements for postoperative ICU monitoring, if appropriate, should be instituted early. Clear communication must be established between the surgical team and anesthesia personnel so that an appropriate anesthetic management plan can be formulated and any specialized equipment required can be mobilized in the operating room (OR). The induction of anesthesia may coincide with resuscitation. Accordingly, the surgical team must be immediately available to help with difficult intravenous (IV) access, emergency tracheostomy, and cardiopulmonary resuscitation. Patients in shock may not tolerate standard anesthetics, which characteristically blunt sympathetic outflow. The anesthetic dose must be judiciously titrated, and Choice of Anesthesia Anesthesia may be classified into three broad categories: (1) general anesthesia, (2) regional anesthesia, and (3) monitored anesthesia care. General anesthesia can be defined as a state of insensibility characterized by loss of consciousness, amnesia, analgesia, and muscle relaxation. This state may be achieved either with a single anesthetic or, in a more balanced fashion, with a combination of several drugs that specifically induce hypnosis, analgesia, amnesia, and paralysis. There is, at present, no consensus as to which general anesthetic regimen best preserves organ function. General anesthesia is employed when contraindications to regional anesthesia are present or when regional anesthesia or monitored anesthesia care fails to provide adequate intraoperative analgesia. In addition, a few situations specifically mandate general anesthesia and controlled ventilation: the need for abdominal muscle paralysis, lung isolation, and hyperventilation; the presence of serious cardiorespiratory instability; and the lack of sufficient time to perform regional anesthesia. Alternatives to general anesthesia should be considered for patients who are susceptible to malignant hyperthermia (MH), for those in whom intubation is likely to prove difficult or the risk of aspiration is high, and for those with pulmonary compromise that may worsen after intubation and positive pressure ventilation. Regional anesthesia is achieved by interfering with afferent or efferent neural signaling at the level either of the spinal cord (neuraxial blockade) or of the peripheral nerves. Neuraxial anesthesia (i.e., epidural or spinal administration of local anesthetics) is commonly employed as the sole anesthetic technique for procedures involving the lower abdomen and the lower extremities; it also provides effective pain relief after intraperitoneal and intrathoracic procedures. Combining regional and general anesthesia has become increasingly popular.19 Currently, some physicians are using neuraxial blockade as the sole anesthetic technique for procedures such as thoracotomy and coronary artery bypass grafting, which are traditionally thought to require general anesthesia and endotracheal intubation.20 Neuraxial blockade has several advantages over general anesthesia, including better dynamic pain control, shorter duration of paralytic ileus, reduced risk of pulmonary complications, and decreased transfusion requirements; it is also associated with a decreased incidence of renal failure and myocardial infarction [see 1:6 Postoperative Pain].21–24 Contrary to conventional thinking, however, the type of anesthesia used (general or neuraxial) is not an independent risk factor for long-term cognitive dysfunction.25 Neuraxial blockade is an essential component of multimodal rehabilitation programs aimed at optimization of perioperative care and acceleration of recovery [see ECP:3 Perioperative Considerations for Anesthesia].26,27 For short, superficial procedures, a variety of peripheral nerve blocks may be considered.28 With procedures on the upper or lower extremity, an IV regional (Bier) block with diluted lidocaine may be useful. Anesthesia of the upper extremity and shoulder may be achieved with the brachial plexus block. Anesthesia of the lower extremity may be 11/08 © 2008 BC Decker Inc 1 BASIC SURGICAL AND PERIOPERATIVE CONSIDERATIONS achieved by blocking the femoral, obturator, and lateral femoral cutaneous nerves (knee surgery) or the ankle and popliteal sciatic nerves (foot surgery). Anesthesia of the thorax may be achieved with intercostal or intrapleural nerve blocks. Anesthesia of the abdomen may be achieved with celiac plexus and paravertebral blocks. Anesthesia of the head and neck may be achieved by blocking the trigeminal, supraorbital, supratrochlear, infraorbitral, and mental nerves and the cervical plexus. Local infiltration of the operative site may provide intraoperative and postoperative analgesia. Unlike the data on neuraxial blockade, the data on peripheral nerve blockade neither support nor discourage its use as a substitute for general anesthesia. Generally, however, we favor regional techniques when appropriate: such approaches maintain consciousness and spontaneous breathing while causing only minimal depression of the CNS and the cardiorespiratory systems, and they yield improved pain control in the immediate postoperative period. Monitored anesthesia care involves the use of IV drugs to reduce anxiety, provide analgesia, and alleviate the discomfort of immobilization. This approach may be combined with local infiltration analgesia provided by the surgeon.29 Monitored anesthesia care requires monitoring of vital signs and the presence of an anesthesiologist who is prepared to convert to general anesthesia if necessary. Its benefits are substantially similar to those of regional anesthesia. These benefits are lost when attempts are made to overcome surgical pain with excessive doses of sedatives and analgesics. Patient Monitoring Patient monitoring is central to the practice of anesthesia. A trained, experienced physician is the only truly indispensable monitor; mechanical and electronic monitors, although useful, are, at most, aids to vigilance. Wherever anesthesia is administered, the proper equipment for pulse oximetry, blood pressure measurement, electrocardiography, and capnography should be available. At each anesthesia workstation, equipment for measuring temperature, a peripheral nerve stimulator, a stethoscope, and appropriate lighting must be immediately available. A spirometer must be available without undue delay. Additional monitoring may be indicated, depending on the patient’s health, the type of procedure to be performed, and the characteristics of the practice setting. Cardiovascular monitoring, including measurement of systemic arterial, central venous, pulmonary arterial, and wedge pressures; cardiac output; and continuous arterial and mixed venous oximetry, is covered in detail elsewhere [see 8:3 Shock]. Additional information about the cardiovascular system may be obtained by transesophageal echocardiography.30 Practice guidelines for this technique have been developed.31 It may be particularly useful in patients who are undergoing valve repair or who have persistent severe hypotension of unknown etiology. The effects of anesthesia on the CNS may be assessed by monitoring electroencephalographic (EEG) activity that is either spontaneous (raw or processed) or evoked (e.g., somatosensory, auditory, or visual). Commercially available devices that employ spectral analysis of spontaneous EEG activity (e.g., bispectral index) are relatively easy to use and 11/08 ACS Surgery: Principles and Practice 3 PERIOPERATIVE CONSIDERATIONS FOR ANESTHESIA — 6 are advocated by some as measures of hypnosis to guide the administration of anesthetics.32,33 However, their effectiveness in preventing intraoperative awareness remains controversial, particularly when anesthesia is maintained by inhalational drugs.34 CNS function may also be assessed by measurement of cerebral blood flow, using transcranial Doppler, jugular bulb venous oxygen saturation, and cerebral oximetry monitoring techniques. Although there is growing clinical experience with these noninvasive intraoperative neurologic monitors, randomized, prospective, and adequately powered studies to support and guide their use are currently lacking. General Anesthesia Techniques An ever-expanding armamentarium of drugs is available for premedication and for induction and maintenance of anesthesia. Selection of one agent over another is influenced by the patient’s baseline condition, procedure, local standard of practice, and predicted duration of hospitalization. premedication Preoperative medications are given primarily to decrease anxiety, to reduce the incidence of nausea and vomiting, and to prevent aspiration. Other benefits include sedation, amnesia, analgesia, drying of oral secretions, and blunting of undesirable autonomic reflexes. Sedatives and Analgesics Benzodiazepines produce anxiolysis, sedation, hypnosis, amnesia, and muscle relaxation; they do not produce analgesia. They may be classified as short acting (midazolam), intermediate acting (lorazepam), or long acting (diazepam). Adverse effects [see Table 5] may be marked in debilitated patients. Their central effects may be antagonized with flumazenil. Muscarinic antagonists (e.g., scopolamine and atropine) were commonly administered at one time; this practice is not as popular today. They produce, to varying degrees, sedation, amnesia, lowered anesthetic requirements, diminished nausea and vomiting, reduced oral secretions, and decreased gastric hydrogen ion secretion. They blunt the cardiac parasympathetic reflex responses that may occur during certain procedures (e.g., ocular surgery, traction on the mesentery, and manipulation of the carotid body). Adverse effects include Table 5 Benzodiazepines: Doses and Duration of Action85 Benzodiazepine Dose (for Sedation) Elimination Half-Life Comments Midazolam 0.5–1.0 mg, repeated 1.7–2.6 hr Respiratory depression, excessive sedation, hypotension, bradycardia, anticonvulsant activity (withdrawal) Lorazepam 0.25 mg, repeated 11–22 hr See midazolam Venous thrombosis Diazepam 2.0 mg, repeated 20–50 hr See midazolam and lorazepam © 2008 BC Decker Inc 1 BASIC SURGICAL AND PERIOPERATIVE CONSIDERATIONS tachycardia, heat intolerance, inhibition of gastrointestinal (GI) motility and micturition, and mydriasis. Opioids are used when analgesia, in addition to sedation and anxiolysis, is required. With morphine and meperidine, the time of onset of action and the peak effect are unpredictable. Synthetic opioids (e.g., fentanyl) have a more rapid onset and a predictable time course, which make them more suitable for premedication immediately before surgery. Adverse effects [see Table 6] can be reversed with full (naloxone) or partial (nalbuphine) antagonists. The alpha2-adrenergic agonists clonidine and dexmedetomidine are sympatholytic drugs that also exert sedative, anxiolytic, and analgesic effects. They reduce intraoperative anesthetic requirements, thus allowing faster recovery, and attenuate sympathetic activation secondary to intubation and surgery, thus improving intraoperative hemodynamic stability. Major drawbacks are hypotension and bradycardia; rebound hypertensive crises may be precipitated by their discontinuance.35,36 Prevention of Aspiration Aspiration of gastric contents is an extremely serious complication that is associated with significant morbidity and mortality. Fasting helps reduce the risk of this complication [see Table 3]. When the likelihood of aspiration is high, ACS Surgery: Principles and Practice 3 PERIOPERATIVE CONSIDERATIONS FOR ANESTHESIA — 7 pharmacologic treatment may be helpful [see Table 7]. H2 receptor antagonists (e.g., cimetidine, ranitidine, and famotidine) and proton pump inhibitors (e.g., omeprazole) reduce gastric acid secretion, thereby raising gastric pH without affecting gastric volume or emptying time. Nonparticulate antacids (e.g., sodium citrate) neutralize the acidity of gastric contents. Metoclopramide promotes gastric emptying (by stimulating propulsive GI motility) and decreases reflux (by increasing the tone of the esophagogastric sphincter); it may also possess antiemetic properties. In all patients at risk for aspiration who require general anesthesia, a rapid sequence induction is traditionally considered a standard of practice, although this has been recently questioned.37 A rapid sequence induction is achieved through adequate preoxygenation, administration of drugs to produce rapid loss of consciousness and paralysis, and exertion of pressure on the cricoid cartilage (the Sellick maneuver) as loss of consciousness occurs to occlude the esophagus and so limit reflux of gastric contents into the pharynx. An alternative is the so-called modified rapid sequence induction, which permits gentle mask ventilation during the application of cricoid pressure (thereby potentially reducing or abolishing insufflation of gas into the stomach). The advantages of the modified approach are that there is less risk of hypoxia and more time to treat cardiovascular responses to induction Table 6 Opioids: Doses and Duration of Action86 Agent Induction Relative Analgesic Potency Maintenance Dose Induction or Loading Maintenance Time to Peak Effect Duration of Action 2–7 hr Comments Morphine 1 1 mg/kg For perioperative analgesia: 0.1 mg/kg IV, IM 0.05–0.2 mg/kg/hr 5–20 min Respiratory depression, nausea, vomiting, pruritus, constipation, urinary retention, biliary spasm, neuroexcitation Pseizure, tolerance Cough suppression, relief of dyspnea-induced anxiety (common to all opioids) Histamine release, orthostatic hypotension, prolonged emergence Meperidine 0.1 For perioperative analgesia: 0.5–1.5 mg/kg IV, IM, SC NA 2 hr (oral); 2–4 hr 1 hr (SC, IM) See morphine Orthostatic hypotension, myocardial depression, dry mouth, mild tachycardia, mydriasis, histamine release Attenuates shivering; to be avoided with MAOIs Local anesthetic–like effect Remifentanil 250–300 1 µg/kg 0.25–0.4 µg/kg/min 3–5 min 5–10 min See morphine Awareness, bradycardia, muscle rigidity Ideal for infusion; fast recovery, no postoperative analgesia Alfentanil 7.5–25 50–300 µg/kg 1.25–8.0 µg/kg/min 1–2 min 10–15 min See morphine Awareness, bradycardia, muscle rigidity Fentanyl 75–125 5–30 µg/kg 0.25–0.5 µg/kg/min 5–15 min 30–60 min See morphine and alfentanil Sufentanil 525–625 2–20 µg/kg 0.05–0.1 µg/kg/min 3–5 min 20–45 min See morphine and alfentanil Ideal for prolonged infusion IM = intramuscular; IV = intravenous; MAOI = monoamine oxidase inhibitor; NA = not applicable; SC = subcutaneous. 11/08 © 2008 BC Decker Inc 1 BASIC SURGICAL AND PERIOPERATIVE CONSIDERATIONS ACS Surgery: Principles and Practice 3 PERIOPERATIVE CONSIDERATIONS FOR ANESTHESIA — 8 Table 7 Pharmacologic Prevention of Aspiration87,88 Agent Dose H2 receptor antagonists Cimetidine Ranitidine Famotidine 300 mg, PO 50 mg IV 20 mg IV Sodium citrate Timing of Administration before Operation Comments 1–3 hr Hypotension, bradycardia, heart block, increased airway resistance, CNS dysfunction, reduced hepatic metabolism of certain drugs Bradycardia Rare CNS dysfunction 30 mL PO 20–30 min Increased gastric fluid volume Omeprazole 40 mg IV 40 min Possible alteration of GI drug absorption, hepatic metabolism Metoclopramide 10 mg IV 15–30 min Extrapyramidal reactions, agitation, restlessness (large doses); to be avoided with MAOIs, pheochromocytoma, bowel obstruction CNS = central nervous system; GI = gastrointestinal; IV = intravenous; MAOI = monoamine oxidase inhibitor; PO = oral. agents before intubation. Regardless of which technique is used, consideration should be given to emptying the stomach via an orogastric or nasogastric tube before induction. induction Induction of general anesthesia is achieved by administering drugs to produce unconsciousness. It is one of the most crucial and potentially dangerous moments for the patient during general anesthesia because of the precipitous depression of the cardiorespiratory systems and airway protective mechanisms. Various agents can be used for this purpose; the choice depends on the patient’s baseline medical condition and fasting status, the state of the airway, the surgical procedure, and the expected length of the hospital stay. The agents most commonly employed for induction are propofol, sodium thiopental, ketamine, and etomidate [see Table 8]. The opioids alfentanil, fentanyl, sufentanil, and remifentanil may also be used for this purpose; they are associated with a very stable hemodynamic profile during induction and surgery but only invariably produce unconsciousness [see Table 6]. Volatile agents [see Table 9] may be employed for induction of general anesthesia when maintenance of spontaneous ventilation is of paramount importance (e.g., with a difficult airway) or when bronchodilation is required (e.g., with severe Table 8 Agent hyperreactive airway disease). Inhalation induction is also popular for ambulatory surgery when paralysis is not required. Sevoflurane is well suited for this application because it is not irritating on inhalation, as are most other volatile agents, and it produces rapid loss of consciousness. Sevoflurane has mostly replaced halothane as the agent of choice for inhalation induction because it is less likely to cause dysrhythmias and is not hepatotoxic. maintenance Balanced general anesthesia is produced with a variety of drugs to maintain unconsciousness, prevent recall, and provide analgesia. Various combinations of volatile and IV agents may be employed to achieve these goals. The volatile agents isoflurane, desflurane, and sevoflurane are commonly used for maintenance [see Table 9]. Nitrous oxide is a strong analgesic and a weak anesthetic agent that possesses favorable pharmacokinetic properties (fast onset, fast offset). Because of its relatively high blood:gas partition coefficient compared with nitrogen, nitrous oxide rapidly difuses into and expands air-filled cavities. Thus, it should be avoided in situations in which expansion of such cavities is undesirable (e.g., pneumothorax, air embolism, bowel obstruction, and middle ear surgery). It cannot be used as the sole anesthetic agent unless Induction Agents: Doses and Duration of Action85 Induction Dose (mg/kg) Time to Peak Effect (s) Duration of Action (min) Comments Propofol 1.0–2.5 90–100 5–10 Hypotension, apnea, antiemetic (low dose), sexual fantasies and hallucinations, convulsions Pseizures (rare), pain on injection, thrombophlebitis Thiopental 2.5–4.5 60 5–8 Hypotension, apnea, emergence delirium, prolonged somnolence, anaphylactoid reaction, injection pain, hyperalgesia Anticonvulsant effect Contraindicated with porphyria Ketamine 0.5–2 30 10–15 Analgesia; increased BP, HR, CO; lacrimation and salivation; bronchial dilatation; elevated ICP Dreaming, illusions, excitement Preservation of respiration (apnea possible with high doses) Etomidate 0.2–0.6 60 4–10 Minor effects on BP, HR, CO Adrenocortical suppression, injection pain and thrombophlebitis, myoclonus, nausea and vomiting BP = blood pressure; CO = cardiac output; HR = heart rate; ICP = intracranial pressure. 11/08 © 2008 BC Decker Inc 1 BASIC SURGICAL AND PERIOPERATIVE CONSIDERATIONS Table 9 Volatile Drugs89,90 Agent Halothane Oil/Gas Coefficient* 224 † MAC (atm) Blood/Gas Coefficient‡ Rank Order (FA/FI)§ 0.0074 2.5 6 Enflurane 96.5 0.0168 1.8 5 Isoflurane 90.8 0.0115 1.4 4 ACS Surgery: Principles and Practice 3 PERIOPERATIVE CONSIDERATIONS FOR ANESTHESIA — 9 hydrolysis of remifentanil, its administration may be labor intensive, necessitating frequent administration of boluses and constant vigilance. Its short half-life also limits its usefulness as an analgesic in the postoperative period and may even contribute to acute opioid intolerance. To help circumvent these problems, various dosing regimens have been proposed in which the patient is switched from remifentanil to a longer-acting narcotic. Desflurane 18.7 0.060 0.45 2 neuromuscular blockade Sevoflurane 47.2 0.0236 0.65 3 1.04 0.47 1 The reversible paralysis produced by neuromuscular blockade improves conditions for endotracheal intubation and facilitates surgery. Neuromuscular blocking agents are classified as either depolarizing (succinylcholine) or nondepolarizing (pancuronium, rocuronium, vecuronium, atracurium, cisatracurium, and mivacurium) and may be further differentiated on the basis of chemical structure and duration of action [see Table 10]. The blocking effect of nondepolarizing muscle relaxants is enhanced by volatile drugs, hypothermia, acidosis, certain antibiotics, magnesium sulfate, and local anesthetics and is reduced by phenytoin and carbamazepine. Patients with weakness secondary to neuromuscular disorders (e.g., myasthenia gravis and Eaton-Lambert syndrome) may be particularly sensitive to nondepolarizing muscle relaxants. Nitrous oxide 1.4 FA/FI = alveolar concentration of gas/inspired concentration; MAC = minimum alveolar concentration to abolish purposeful movement in response to noxious stimulation in 50% of patients. *Lipid solubility correlates closely with anesthetic potency (Meyer-Overton rule). † Correlates closely with lipid solubility. ‡ Relative affinity of an anesthetic for blood compared to gas at equilibrium. The larger the coefficient, the greater the affinity of the drug for blood and hence the greater the quantity of drug contained in the blood. § Rise in alveolar anesthetic concentration toward the inspired concentration is most rapid with the least soluble drugs and slowest with the most soluble. it is administered in a hyperbaric chamber; it is usually administered with at least 30% oxygen to prevent hypoxia. Nitrous oxide is commonly used in combination with other volatile agents. Potent volatile agents can trigger malignant hyperthermia in susceptible patients. The IV drugs currently used to maintain general anesthesia, whether partially or entirely, feature a short, contextsensitive elimination half-life; thus, pharmacologically significant drug accumulation during prolonged infusion is avoided. Such agents (including propofol, midazolam, sufentanil, and remifentanil) are typically administered via computercontrolled infusion pumps that use population-based pharmacokinetic data to establish stable plasma (and CNS effector site) concentrations. Because of the extremely rapid emergence General anesthesia is terminated by cessation of drug administration, reversal of muscle paralysis, and extubation (or removal of an upper airway device). During this potentially dangerous period, close scrutiny of the patient is essential, and all OR personnel must coordinate their efforts to help ensure a smooth and safe emergence from general anesthesia. In this phase, patients may demonstrate hemodynamic instability, retching and vomiting, respiratory compromise (including laryngospasm), and, occasionally, uncooperative or aggressive behavior.38 Table 10 Neuromuscular Blocking Agents: Doses and Duration of Action91 Agent Dose (mg/kg) Duration of Action (min) Metabolism Elimination Comments Succinylcholine chloride 0.7–2.5 5–10 Plasma cholinesterase Renal < 2%, hepatic 0% Fasciculations, elevation of serum potassium, increased ICP, bradycardia, MH trigger; prolonged effect in presence of atypical pseudocholinesterase Pancuronium 0.04–0.1 60–120 Hepatic 10–20% Renal 85%, hepatic 15% Muscarinic antagonist (vagolytic), prolonged paralysis (long-term use) Rocuronium 0.6–1.2 35–75 None Renal < 10%, hepatic > 70% Minimal histamine release Vecuronium 0.08–0.1 45–90 Hepatic 30–40% Renal 40%, hepatic 60% Prolonged paralysis (long-term use) Atracurium 0.3–0.5 30–45 Hoffman elimination, nonspecific ester hydrolysis Renal 10–40%, hepatic 0% Histamine release; laudanosine metabolite (a CNS stimulant) Cisatracurium 0.15–0.2 40–75 Hoffman elimination Renal 16%, hepatic 0% Negligible histamine release; laudanosine metabolite Mivacurium 0.15–0.2 15–20 Plasma cholinesterase Renal < 5%, hepatic 0% Histamine release; prolonged effect in presence of atypical pseudocholinesterase CNS = central nervous system; ICP = intracranial pressure; MH = malignant hyperthermia. 11/08 © 2008 BC Decker Inc 1 BASIC SURGICAL AND PERIOPERATIVE CONSIDERATIONS Reversal of neuromuscular blockade is achieved by administering anticholinesterases such as neostigmine or edrophonium. These drugs should be given in conjunction with a muscarinic antagonist (atropine or glycopyrrolate) to block their unwanted parasympathomimetic side effects. Neostigmine is more potent than edrophonium in reversing profound neuromuscular blockade. It is imperative that paralysis be sufficiently reversed before extubation to ensure that spontaneous respiration is adequate and that the airway can be protected. Reversal can be clinically verified by confirming the patient’s ability to lift the head for 5 seconds. Reversal can also be assessed by muscle contraction response to electrical nerve stimulation. Causes of failure to emerge from anesthesia include residual neuromuscular blockade, a benzodiazepine or opioid overdose, the central anticholinergic syndrome, an intraoperative cerebrovascular accident, preexisting pathophysiologic conditions (e.g., CNS disorders, hepatic insufficiency, and drug or alcohol ingestion), electrolyte abnormalities, acidosis, hypercarbia, hypoxia, hypothermia, and hypothyroidism. As noted, the effects of narcotics and benzodiazepines can be reversed with naloxone and flumazenil, respectively. Physostigmine may be given to reverse the reduction in consciousness level produced by general anesthetics. Electrolyte, glucose, blood urea nitrogen, and creatinine levels should be measured; liver and thyroid function tests should be performed; and arterial blood gas values should be obtained. Patients should be normothermic. Unexplained failure to emerge from general anesthesia warrants immediate consultation with a neurologist. ACS Surgery: Principles and Practice 3 PERIOPERATIVE CONSIDERATIONS FOR ANESTHESIA — 10 the headrest used in the prone position.41 The relationship between postoperative cognitive dysfunction (POCD) and anesthesia per se remains unclear and may occur in patients who receive general (intravenous or inhalational) or regional anesthesia. POCD does not seem to be associated with intraoperative hypoxemia, hypotension, or acid-base disturbances. Certain procedures, such as cardiac and orthopedic surgery, have been associated with this disorder, and a common etiology (air, particulate, or fat microemboli) is implicated. There is a growing appreciation that even with other types of surgery, POCD can occur, with elderly patients (more than 60 years) being at particular risk during the first week after the procedure. Presently, there is little evidence that POCD persists longer than 6 months.42 Regional Anesthesia Techniques Neuraxial (central) anesthesia techniques involve continuous or intermittent injection of drugs into the epidural or intrathecal space to produce sensory analgesia, motor blockade, and inhibition of sympathetic outflow. Peripheral nerve blockade involves inhibition of conduction in fibers of a single peripheral nerve or plexus (cervical, brachial, or lumbar) in the periphery. Intravenous regional anesthesia involves IV administration of a local anesthetic into a tourniquet-occluded extremity. Perioperative pain control may be facilitated by administering local anesthetics, either infiltrated into the wound or sprayed into the wound cavity. Procedures performed solely under infiltration may be associated with patient dissatisfaction caused by intraoperative anxiety and pain.43,44 contraindications Risk and General Anesthesia Determining the risk(s) attributed solely to anesthesia is difficult because of the confounding variables of patient characteristics, concurrent medications, and the surgical procedure itself, including context (e.g., elective versus emergency). Prospective, unbiased studies sufficiently powered to reveal the frequency of rare events are lacking, and reliance on self-reporting of negative outcomes likely results in an underestimation of risk. Given these limitations, attempts have been made to define the risks associated with anesthesia, based on extensive and critical literature reviews [see Table 11].39 Perioperative mortality associated with anesthesia increases with age, ASA status, and emergency procedures. Factors contributing to anesthesia-related mortality include inadequate assessment, preparation and resuscitation, inappropriate anesthetic technique, inadequate perioperative monitoring, lack of supervision, and poor postoperative care. Morbidity ranges from major permanent disability to relatively minor events without long-term consequence. Peripheral nerve injury, although rare, may have serious disability. The etiology includes direct injury from needles, instruments, suturing, injection of toxic substances, and thermal insults. Less obvious but more frequent events involve mechanical factors such as nerve compression or stretch. Ischemia associated with a low cardiac output state is often implicated.40 Great caution must be used during patient positioning, with careful attention to proper padding. Loss of vision is a rare but catastrophic event that may be associated with compression of the eye by a facemask or by padding of 11/08 Strong contraindications to regional (particularly neuraxial) anesthesia include patient refusal or inability to cooperate during the procedure, elevated intracranial pressure, anticoagulation, vascular malformation or infection at the needle insertion site, severe hemodynamic instability, and sepsis. Preexisting neurologic disease is a relative contraindication. anticoagulation and bleeding risk Although hemorrhagic complications can occur after any regional technique, bleeding associated with neuraxial blockade is the most serious possibility because of its devastating consequences. Spinal hematoma may occur as a result of vascular trauma from placement of a needle or catheter into the subarachnoid or epidural space. Spinal hematoma may also occur spontaneously, even in the absence of antiplatelet or anticoagulant therapy. The actual incidence of spinal cord injury resulting from hemorrhagic complications is unknown; the reported incidence is estimated to be less than 1 in 150,000 for epidural anesthesia and 1 in 200,000 for spinal anesthesia [see Table 12].45 With such low incidences, it is difficult to determine whether any increased risk can be attributed to anticoagulant use [see Table 13] without data from millions of patients, which are not currently available. Much of our clinical practice is based on small surveys and expert opinion. Antiplatelet Agents There is no universally accepted test that can guide antiplatelet therapy. Antiplatelet agents can be divided into © 2008 BC Decker Inc 1 BASIC SURGICAL AND PERIOPERATIVE CONSIDERATIONS ACS Surgery: Principles and Practice 3 PERIOPERATIVE CONSIDERATIONS FOR ANESTHESIA — 11 Table 11 Predicted Incidence of Complications of Anesthesia39 Mortality and Morbidity Approximate Incidence Rate per 10,000 Population Remarks Total perioperative deaths (within 30 days) 1:200 (elective surgery) 1:40 (emergency surgery) x2 (60–79 yr) x5 (80–89 yr) x7 (> 90 yr) 50 250 Death related to anesthesia 1:50,000 (anesthesia related) 1:100,000 (ASA physical status I and II) 0.2 0.1 Cardiac arrest 1:10,000–1:20,000 (general anesthesia) 1:3,000 (local anesthesia) 1:1,500 (spinal: 25% fatal) Myocardial reinfarction 1:20 (0–3 mo after myocardial infarction 1:40 (4–6 mo after myocardial infarction) 500 Aspiration during general anesthesia 1:3,000 1:60,000 (death) 3 0.16 Difficult intubation 1:50 200 Failure to intubate 1:500 20 Failure to intubate and ventilate 1:5,000 2 Postoperative cognitive dysfunction (> 60 yr) 1:4 at 1 wk 1:10 at 3 mo 1:100 permanent 2,500 1,000 100 Regional anesthesia General anesthesia Postoperative delirium 1:7 (general surgery) Up to 1:2 for elderly fractures of neck or femur 1,400 5,000 x3 >75 yr x3 if requiring intensive care Drowsiness 1:2 5,000 Day surgery Dizziness 1:5 2,000 Day surgery Headache 1:5 2,000 Cerebrovascular accident (CVA) 1:50 if previous stroke 1:100 general surgery 200 100 Carotid endarterectomy (CVA + death) 1:15 if symptomatic 1:25 if asymptomatic 700 400 0.5–1.0 3 7 Mortality ≈ 1:15,000–1:150,000 250 Respiratory complications x4 in emergencies x3 in obstetrics Obstetrics ≈ 1:250 46% mortality 60% mortality if previous CVA (≈ 1:700 in the nonsurgical population) Disabling CVA + death Awareness With pain 1:3,000 3 2/3 with neuromuscular blockade Without pain 1:300 30 1/3 without neuromuscular blockade Total intravenous anesthesia 1:500 1:10,000 20 1 1:10,000 1 “Idiopathic” (general anesthesia) 1:10,000 1 Transient after spinal anesthesia 1:7 1,500 Loss of vision 1:125,000 1:100 (cardiac surgery) 0.08 100 Pain ~1:3 (moderate) 3,000 1:10 (severe) 1,000 Anaphylaxis Deafness After major surgery Day surgery Postoperative nausea and vomiting 1:2 5,000 1:4 2,500 ≈ 1:1,000 cardiac surgery 2/3 nausea and 1/3 vomiting Female:male 3:1 11/08 © 2008 BC Decker Inc 1 BASIC SURGICAL AND PERIOPERATIVE CONSIDERATIONS ACS Surgery: Principles and Practice 3 PERIOPERATIVE CONSIDERATIONS FOR ANESTHESIA — 12 Table 11 Continued Mortality and Morbidity Sore throat Approximate Incidence 1:2 (if tracheal tube) 1:5 (if laryngeal mask) 1:10 (if facemask only) Rate per 10,000 Population Remarks 5,000 2,000 1,000 Dental damage Requiring intervention 1:5,000 All dental damage 1:100 All oral trauma after tracheal 1:20 intubation 2 100 500 Peripheral nerve injury 1:300 ulnar neuropathy 30 General anesthesia 1:1,000 (other nerves) 10 Thrombophlebitis 1–2:20 (water-soluble drugs) 1:4 (propylene glycol based) Arterial cannulation complication <1:100 (permanent) Pulmonary artery perforation 1:2,000 500–1,000 2,500 < 100 5 Arterial puncture (during central venous cannulation) Internal jugular vein cannulation 1:35 350 Subclavian vein cannulation 1:200 50 ASA = American Society of Anesthesiologists. four major classes: (1) aspirin and related cyclooxygenase inhibitors (NSAIDs); (2) ticlopidine and selective adenosine diphosphate antagonists; (3) direct thrombin inhibitors (e.g., hirudin); and (4) glycoprotein IIb/IIIa inhibitors. Only with aspirin is there sufficient experience to suggest that it does not increase the risk of spinal hematoma when given at clinical dosages.46 Caution should, however, be exercised when aspirin is used in conjunction with other anticoagulants.47 Oral Anticoagulants Therapeutic anticoagulation with warfarin is a contraindication to regional anesthesia.48 If regional anesthesia is planned, oral warfarin can be replaced with IV heparin (see below). Heparin There does not seem to be an increased risk of spinal bleeding in patients receiving subcutaneous low-dose (5,000 U) unfractionated heparin [see 6:6 Venous Thromboembolism] if the interval between administration of the drug and initiation of the procedure is greater than 4 hours.49 Higher doses, however, are associated with increased risk. If neuraxial anesthesia or epidural catheter removal is planned, heparin infusion must be discontinued for at least 6 hours, and the partial thromboplastin time should be measured. Recommendations for standard heparin cannot be extrapolated to low-molecular-weight heparin (LMWH), because the biologic actions of LMWH are different and the effects cannot be monitored by conventional coagulation measurements. After the release of LMWH for general use in the United States in 1993, more than 40 spinal hematomas were reported 11/08 during a 5-year period. LMWH should be stopped at least 24 hours before regional blockade, and the first postoperative dose should be given no sooner than 24 hours afterward.47 complications Drug Toxicity Systemic toxic reactions to local anesthetics primarily involve the CNS and the cardiovascular system [see Table 14]. The initial symptoms are light-headedness and dizziness, followed by visual and auditory disturbances. Convulsions and respiratory arrest may ensue and necessitate treatment and resuscitation. The use of neuraxial analgesic adjuncts (e.g., opioids, clonidine, epinephrine, and neostigmine) decreases the dose of local anesthetic required, speeds recovery, and improves the quality of analgesia. The side effects of such adjuncts include respiratory depression (opiods), urinary retention (opiods), tachycardia (epinephrine), hypotension (clonidine), and nausea and vomiting (neostigmine, opioids). Neurologic Complications The incidence of neurologic complications ranges from 2 in 10,000 to 12 in 10,000 with epidural anesthesia and from 0.3 in 10,000 to 70 in 10,000 with spinal anesthesia.49,50 The most common serious complication is neuropathy, followed by cranial nerve palsy, epidural abscess, epidural hematoma, anterior spinal artery syndrome, and cranial subdural hematoma [see Table 12]. Vigilance and routine neurologic testing of sensory and motor function are of paramount importance for early detection and treatment of these potentially disastrous complications. © 2008 BC Decker Inc 1 BASIC SURGICAL AND PERIOPERATIVE CONSIDERATIONS ACS Surgery: Principles and Practice 3 PERIOPERATIVE CONSIDERATIONS FOR ANESTHESIA — 13 Table 12 Predicted Incidence of Complications of Regional Anesthesia39 Complication Paraplegia Incidence Rate per 10,000 Population ≈ 1:100,000 0.1 1–3:10,000 1–3 Remarks Permanent nerve injury Spinal Epidural 0.3–10:10,000 Peripheral nerve block ≈ 1:5,000 Epidural hematoma Epidural abscess Transient neural complications 0.07 ≈ 1:200,000 (spinal) 0.05 1:2,000–1:7,500 1:1,000–1:10,000 (epidural) Transient radicular irritation (spinal) Up to 1:3 (heavy lidocaine and mepivacaine) Cardiac arrest ≈ 1:1,500 (spinal) ≈ 1:3,000 (local anesthesia) Backache 2 ≈ 1:150,000 (epidural) 1:125–1:2,500 (spinal) Post–dural puncture headache 0.03–10 1:1,000,000 (spontaneous) 1:14,000 (USA) 1:2,250,000 (Europe) 1:10,000 (spontaneous) 1–10 (epidural) 4-80 (spinal) 3,000 5 (spinal) 3 (local anesthesia) 1 (epidural) ≈ 1:10,000 (regional blocks) 1 (regional) 100 80% following inadvertent dural tap ≈ 1:10 (day surgery) 1,000 Blood patch 70–100% Immediate success, but headaches recur in 30–50% < 1 hr surgery ≈ 20% 2,000 GA = LA > 4 hr surgery ≈ 50% 5,000 Urinary dysfunction ≈ 1:50 200 Pneumothorax ≈ 1:20 (supraclavicular blocks) 500 Systemic LA toxicity ≈ 1:10,000 (epidural) ≈ 1:1,500 (regional blocks) Cerebral seizures ≈ ≈ ≈ ≈ 0.7–5.0 ≈ 1:10,000 (epidural) ≈ 1:100 2% brachial plexus neuropraxia lasting > 3 mo 1 7 ≈ 1:4,000 (intravenous regional anesthesia) 2.5 Axillary ≈ 1:1,000 ≈ 1:500 (brachial plexus) 20 Supraclavicular ≈ 1:125 Eye blocks Retrobulbar hemorrhage 1:250–1:20,000 0.5–40 Brainstem anesthesia ≈ 1:700 15 Globe perforation ≈ 1:10,000 1 Ptosis—transient after eye block ≈ 1:2 at 24 hr 5,000 ≈ 1:5 at 1 mo 2,000 Diplopia—transient after eye block 8–70% 800–7,000 GA = general anesthesia; LA = local anesthesia. Transient Neurologic Symptoms The term transient neurologic symptoms (TNSs) refers to backache with pain radiating into the buttocks or the lower extremities after spinal anesthesia. It occurs in 4 to 33% of patients, typically 12 to 36 hours after the resolution of spinal anesthesia, and lasts for 2 to 3 days.51 TNSs have been described after intrathecal use of all local anesthetics but are most commonly noted after administration of lidocaine, in the ambulatory surgical setting, and with the patient in the lithotomy position during operation. Discomfort from TNSs is self-limited and can be effectively treated with NSAIDs. 11/08 © 2008 BC Decker Inc 1 BASIC SURGICAL AND PERIOPERATIVE CONSIDERATIONS Table 13 Pharmacology of Anticoagulant Agents Drug Coagulation Tests INR PTT IV < (( SC Time to Peak Effect Time to Normal Hemostasis after Discontinuance min 4–6 hr Heparin < ( 1 hr 4–6 hr LMWH < < 2–4 hr 12 hr Warfarin (( < 2–6 days 4–6 days Aspirin < < hr 5–8 days Thrombolytic agents (t-PA, streptokinase) < (( min 1–2 days Post–Dural Puncture Headache Use of small-gauge pencil-point needles for spinal anesthesia is associated with a 1% incidence of PDPH. The incidence of PDPH after epidural analgesia varies substantially because the risk of inadvertent dural puncture with a Tuohy needle is directly dependent on the anesthesiologist’s training. PDPH is characteristically aggravated by upright posture and may be associated with photophobia, neck stiffness, nausea, diplopia, and tinnitus. Meningitis should be considered in the differential diagnosis. Although PDPH is not life-threatening, it carries substantial morbidity in the form of restricted activity. Medical treatment with bed rest, IV fluids, NSAIDs, and caffeine is only moderately effective. An epidural blood patch is the treatment of choice: the success rate is approximately 70%. Admission to the postanesthetic care unit (PACU) is appropriate for patients whose vital signs are stable and whose pain is adequately controlled after emergence from Table 14 Local Anesthetics for Infiltration Anesthesia: Maximum Doses* and Duration of Action Without Epinephrine Airway management is a pivotal component of patient care because failure to maintain airway patency and ventilation can lead to permanent disability, brain injury, or death. The difficult airway should be managed in accordance with contemporary airway guidelines, such as the protocols established by the ASA, to reduce the risk of adverse outcomes during attempts at ventilation and intubation. (The ASA protocols may be accessed on the organization’s Web site: http://www.asahq.org/Newsletters/2005/11-05/2003Trauma Algorithm.html). The emphasis on preserving spontaneous ventilation and the focus on awake intubation options are central themes whose importance cannot be overemphasized. It is crucial that all patients who are undergoing difficult or prolonged airway instrumentation be appropriately treated with topical anesthesia, sedation, and monitoring so as to ensure adequate ventilation and to attenuate, detect, and treat harmful neuroendocrine responses that can cause Table 15 Pharmacologic Treatment of Postoperative Nausea and Vomiting8 Duration Duration Maximum Maximum of Action of Action Dose (mg) Dose (mg) (min) (min) 800 300 300 500 175 300 15–30 30–60 45–90 30–90 120–240 120–180 Dose 1,000 500 500 600 225 400 3–90 120–360 120–360 120–360 180–420 180–420 Comments Propofol 10 mg IV, repeated dose [See Table 8] Ondansetron 4.0–8.0 mg IV Highly effective, costly; headache, constipation, transiently increased LFTs Dexamethasone 4.0–8.0 mg IV Adrenocortical suppression, delayed wound healing, fluid retention, electrolyte disturbances, psychosis, osteoporosis Droperidol 0.5–1.0 mg IV Sedation, restlessness, dysphoria, dysrhythmia (?) Metoclopramide 10–20 mg IV Avoid in bowel obstruction, extrapyramidal reactions Scopolamine 0.1–0.6 mg SC, IM, IV Muscarinic side effects, somnolence Dimenhydrinate 25–50 mg IV Drowsiness, dizziness With Epinephrine (1:200,000) *Recommended maximum dose can be given to healthy, middle-aged, normalsized adults without toxicity. Subsequent doses should not be given for at least 4 hours. Doses should be reduced during pregnancy. 11/08 Special Scenarios Agent Recovery Chloroprocaine Lidocaine Mepivacaine Prilocaine Bupivacaine Etidocaine anesthesia. Patients requiring hemodynamic or respiratory support may be admitted to the PACU if rapid improvement is expected and appropriate monitoring and personnel are available. Hemodynamic instability, the need for prolonged respiratory support, and poor baseline condition mandate admission to the ICU. Common complications encountered in the PACU include postoperative pulmonary insufficiency, cardiovascular instability, acute pain, and nausea and vomiting [see Table 15]. These complications are discussed in greater detail elsewhere [see 8:5 Pulmonary Insufficiency, 8:2 Acute Cardiac Dysrhythmia, 1:6 Postoperative Pain, and ECP:5 Patient Safety in Surgical Care: A Systems Approach]. difficult airway ((= clinically significant increase; ( = possibly clinically significant increase; < = clinically insignificant increase or no effect; INR = international normalized ratio; LMWH = low-molecular-weight heparin; PTT = partial thromboplastin time; t-PA = tissue plasminogen activator. Drug ACS Surgery: Principles and Practice 3 PERIOPERATIVE CONSIDERATIONS FOR ANESTHESIA — 14 IM = intramuscular; IV = intravenous; LFT = liver function test; SC = subcutaneous. © 2008 BC Decker Inc 1 BASIC SURGICAL AND PERIOPERATIVE CONSIDERATIONS myocardial ischemia, bronchospasm, and intracranial hypertension. Extubation is stressful as well and may be associated with intense mucosal stimulation and exaggerated glottic closure reflexes, resulting in laryngospasm and, possibly, pulmonary edema secondary to vigorous inspiratory efforts against an obstructed airway. Laryngeal incompetence and aspiration can also occur after extubation. Removal of an endotracheal tube from a known or suspected difficult airway should ideally be performed over a tube exchanger so as to facilitate emergency reintubation. Alternatives to standard oral airways, masks, introducers, exchangers, laryngoscopes, and endotracheal tubes now exist that offer more options, greater safety, and better outcomes. It would be naive to believe that any single practitioner could master every new airway protocol and device. To keep up with technical and procedural advances, university hospital program directors should consider incorporating technical skill laboratories and simulator training sessions into their curricula. morbid obesity Morbid obesity represents the extreme end of the overweight spectrum and is usually defined as a body mass index higher than 40 kg/m2 [see 5:7 Surgical Treatment of Morbid Obesity].52 It poses a formidable challenge to health care providers in the OR, the postoperative recovery unit, and the ICU. The major concerns in the surgical setting are the possibility of a difficult airway, the increased risk of known or occult cardiorespiratory compromise, and various serious technical problems related to positioning, monitoring, vascular access, and transport. Additional concerns are the potential for underlying hepatic and endocrine disease and the effects of altered drug pharmacokinetics and pharmacodynamics. For the morbidly obese patient, there is no such thing as minor surgery. Initial management should be based on the assumptions that (1) a difficult airway is likely; (2) the patient will be predisposed to hiatal hernia, reflux, and aspiration; and (3) rapid arterial desaturation will occur with induction of anesthesia as a consequence of decreased functional residual capacity and high basal oxygen consumption. Often the safest option is an awake fiberoptic intubation with appropriate topical anesthesia and light sedation. In expert hands, this technique is extremely well tolerated and can usually be performed in less than 10 minutes.53 Morbidly obese patients often are hypoxemic at rest and have an abnormal alveolar-arterial oxygen gradient caused by ventilation-perfusion mismatching. The combination of general anesthesia and the supine position exacerbates alveolar collapse and airway closure. Mechanical ventilation, weaning, and extubation may be difficult and dangerous, especially in the presence of significant obstructive sleep apnea. Postoperative pulmonary complications (e.g., pneumonia, aspiration, atelectasis, and emboli) are common.54 Morbid obesity imposes unusual loading conditions on both sides of the heart and the circulation, leading to the progressive development of insulin resistance, atherogenic dyslipidemias, systemic and pulmonary hypertension, ventricular hypertrophy, and a high risk of premature coronary artery disease and biventricular heart failure. Perioperative cardiac morbidity and mortality are therefore significant problems. Untoward events can happen suddenly, ACS Surgery: Principles and Practice 3 PERIOPERATIVE CONSIDERATIONS FOR ANESTHESIA — 15 and resuscitation is extremely difficult. Cardiorespiratory compromise may be attenuated by effective postoperative pain control that permits early ambulation and effective ventilation. Surgical site infection and dehiscence may result in difficult reoperation and prolonged hospitalization. malignant hyperthermia MH is a rare but potentially fatal genetic condition characterized by life-threatening hypermetabolic reactions in susceptible individuals after the administration of volatile anesthetics or depolarizing muscle relaxants.55 Abnormal function of the sarcoplasmic reticulum calcium release channel in skeletal muscle has been identified as a possible underlying cause. In making the diagnosis of MH, it is important to consider other possible causes of postoperative temperature elevation. Such causes include inadequate anesthesia, equipment problems (e.g., misuse or malfunction of heating devices, ventilators, or breathing circuits), local or systemic inflammatory responses (either related or unrelated to infection), transfusion reaction, hypermetabolic endocrinopathy (e.g., thyroid storm or pheochromocytoma), neurologic catastrophe (e.g., intracranial hemorrhage), and reaction to or abuse of a drug. Immediate recognition and treatment of a fulminant MH episode are essential for preventing morbidity and mortality. Therapy consists of discontinuing all triggers, instituting aggressive cooling measures, giving dantrolene in an initial dose of 2.5 mg/kg, and administering 100% oxygen to compensate for the tremendous increase in oxygen use and carbon dioxide production. An indwelling arterial line, central venous access, and bladder catheterization are indispensable for monitoring and resuscitation. Acidosis, hyperkalemia, and malignant dysrhythmias must be rapidly treated, with the caveat that calcium channel blockers are contraindicated in this setting. Maintenance of adequate urine output is of paramount importance and may be facilitated by the clinically significant amounts of mannitol contained in commercial dantrolene preparations. When the patient is stable and the surgical procedure is complete, monitoring and support are continued in the ICU, where repeat doses of dantrolene may be needed to prevent or treat recrudescence of the disease.55 massive transfusion Massive blood transfusion, defined as the replacement of a patient’s entire circulating blood volume in less than 24 hours, is associated with significant morbidity and mortality. Management of massive transfusion requires an organized multidisciplinary team approach and a thorough understanding of associated hematologic and biochemical abnormalities and subsequent treatment options. Patients suffering from shock as a result of massive blood loss often require transfusions of packed red blood cells, platelets, fresh frozen plasma, and cryoprecipitate to optimize oxygen-carrying capacity and address dilutional and consumptive loss of platelets and clotting factors [see 8:3 Shock and 1:4 Bleeding and Transfusion]. Transfusion of large amounts of blood products into a critically ill patient can lead to coagulopathies, hyperkalemia, acidosis, citrate intoxication, fluid overload, and hypothermia.56 Therapy should be guided by vital signs, urine output, pulse oximetry, electrocardiography, capnography, invasive hemodynamic 11/08 © 2008 BC Decker Inc 1 BASIC SURGICAL AND PERIOPERATIVE CONSIDERATIONS monitoring, serial arterial blood gases, biochemical profiles, and bedside coagulation screens. Fluids should be administered through large-bore cannulas connected to modern countercurrent warming devices. Shed blood should be salvaged and returned to the patient whenever possible. In refractory cases, transcatheter angiographic embolization techniques should be considered for control of bleeding. Hemostatic agents, such as procoagulants (desmopressin, recombinant factor VIIa) and antifibrinolytics (aprotnin, tranexamic acid, e-aminocaproic acid), have been used extensively in surgical procedures associated with considerable blood loss (e.g., solid organ transplantation, cardiac and orthopedic surgery [see 1:4 Bleeding and Transfusion].57 Although they are effective at reducing blood loss, a serious concern is the increased risk for thrombosis. Aprotinin, a serine protease inhibitor with unique antifibrinolytic and hemostatic properties, very effectively decreases blood loss and transfusion requirements, as well as attenuates potentially harmful inflammatory responses and minimizes reperfusion injury. However, recent evidence indicates that it may be associated with increased morbidity58 (renal failure) and mortality,59 so its availability has been suspended.60 Recombinant factor VIIa was originally approved for hemophiliacs who developed antibodies against either factor VIII or factor IX. It may prove useful for managing hemorrhage deriving from trauma or surgery when standard interventions have failed.61 hypothermia Significant decreases in core temperature are common during anesthesia and surgery as a consequence of exposure to a cold OR environment and of disturbances in normal protective thermoregulatory responses. Patients lose heat through conduction, convection, radiation, and evaporation, especially from large wounds and during major intracavitary procedures. Moreover, effective vasoconstrictive reflexes and both shivering and nonshivering thermogenesis are severely blunted by anesthetics.62 Neonates and the elderly are particularly vulnerable. Hypothermia may confer some degree of organ preservation during ischemia and reperfusion. For example, in cardiac surgery, hypothermic cardiopulmonary bypass is a common strategy for protecting the myocardium and the CNS. Intentional hypothermia has also been shown to improve neurologic outcome and survival in comatose victims of cardiac arrest. Perioperative hypothermia can have significant deleterious effects as well, however, including myocardial ischemia, surgical site infection, increased blood loss and transfusion requirements, and prolonged anesthetic recovery and hospital stay. The sensation of cold is highly uncomfortable for the patient, and shivering impedes monitoring, raises plasma catecholamine levels, and exacerbates imbalances between oxygen supply and demand by consuming valuable energy for involuntary muscular activity. It is therefore extremely important to measure the patient’s temperature and maintain thermoneutrality. Increasing the ambient temperature of the OR and applying modern forced-air warming systems are the most effective techniques available. In addition, all IV and irrigation fluids should be heated. After the patient has been transferred from the OR, aggressive treatment of 11/08 ACS Surgery: Principles and Practice 3 PERIOPERATIVE CONSIDERATIONS FOR ANESTHESIA — 16 hypothermia with these techniques should be continued as necessary. Shivering may also be reduced by means of drugs such as meperidine, nefopam, tramadol, physostigmine, ketamine, methylphenidate, and doxapram.63 intraoperative awareness One of the goals of anesthesia is to produce a state of unconsciousness during which the patient neither perceives nor recalls noxious surgical stimuli. When this objective is not met, awareness occurs, and the patient will have explicit or implicit memory of intraoperative events. In some instances, intraoperative awareness develops because human error, machine malfunction, or technical problems result in an inappropriately light level of anesthesia. In others (e.g., when the patient is severely hemodynamically unstable or efforts are being made to avoid fetal depression during cesarean section), the light level of anesthesia may have been intentionally chosen. Regardless of the cause, intraoperative awareness is a terrifying experience for the patient and has been associated with serious long-term psychological sequelae.64 Prevention of awareness depends on regular equipment maintenance, meticulous anesthetic technique, and close observation of the patient’s movements and hemodynamic responses during operation. CNS monitoring may reduce the risk of intraoperative awareness, particularly when anesthesia is maintained exclusively by intravenous drugs (total intravenous anesthesia).34 anaphylaxis Allergic reactions range in severity from mild pruritus and urticaria to anaphylactic shock and death. Inciting agents include, but are not limited to, antibiotics, contrast agents, blood products, volume expanders, protamine, aprotinin, narcotics, induction agents, muscle relaxants, latex,65 and, rarely, local anesthetic solutions. Many drug additives and preservatives have also been implicated. True anaphylaxis presents shortly after exposure to an allergen and is mediated by chemicals released from degranulated mast cells and basophils. Manifestations usually include dramatic hypotension, tachycardia, bronchospasm, arterial oxygen desaturation, and cutaneous changes. Laryngeal edema can occur within minutes, in which case, the airway should be secured immediately. Anaphylaxis can mimic heart failure, asthma, pulmonary embolism, and tension pneumothorax. Treatment involves withdrawing the offending substance and administering oxygen, fluids, and epinephrine, followed by IV steroids, bronchodilators, and histamine antagonists. Prolonged intubation and ICU monitoring may be required until symptoms resolve. Appropriate skin and blood testing should be done to identify the causative agent. perioperative dysrhythmias In 2005, current scientific developments in the acute treatment of cerebrovascular, cardiac, and pulmonary disease were merged with the evolving discipline of evidence-based medicine to produce the most comprehensive set of resuscitation standards ever created: a 14-part document from the American Heart Association entitled “2005 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care.”66 This document addresses a wide array of key issues in both in-hospital and out-of-hospital resuscitation, including a recommendation for © 2008 BC Decker Inc 1 BASIC SURGICAL AND PERIOPERATIVE CONSIDERATIONS confirmation of tube position after endotracheal intubation and a warning about the danger associated with unintentional massive auto–positive end-expiratory pressure. As regards the impact the new guidelines have on the management of cardiopulmonary resuscitation, an increase in ratios of compression to ventilation ratios (to 30:2) and an emphasis on effective chest compressions (“push hard, push fast”) are suggested. In addition, early chest compressions before defibrillation, a one-shock sequence for defibrillation as opposed to a three-shock sequence, and avoidance of prolonged interruption of chest compressions are recommended. For wide QRS dysrhythmias, amiodarone continues to be the drug of choice. It may also be administered for ventricular fibrillation or for pulseless ventricular tachycardia that does not respond to cardiopulmonary resuscitation, cardioversion, and a vasopressor. Amiodarone is a complex, powerful, and broad-spectrum agent that inhibits almost all of the drug receptors and ion channels conceivably responsible for the initiation and propagation of cardiac ectopy, irrespective of underlying ejection fraction, accessory pathway conduction, or anatomic substrate. It does, however, have potential drawbacks, such as its relatively long half-life, its toxicity to multiple organs, and its complicated administration scheme. Furthermore, amiodarone is a potent noncompetitive alpha and beta blocker, which has important implications for anesthetized, mechanically ventilated patients who may be debilitated and experiencing volume depletion, abnormal vasodilation, myocardial depression, and fluid, electrolyte, and acid-base abnormalities. That said, no other drug in its class has ever demonstrated a significant benefit in randomized trials addressing cardiac arrest in humans. Amiodarone is effective in both children and adults, and it can be used for prophylaxis and treatment. The recommended cardiac arrest dose is a 300 mg IV bolus. In less acute situations (e.g., wide-complex tachycardia), an initial 150 mg dose should be administered slowly over 10 minutes, and one or two additional boluses may be given similarly. A loading regimen is then initiated, first at 1 mg/min for 6 hours and then at 0.5 mg/min for 18 hours. Vasopressin (antidiuretic hormone) continues to be listed as an alternative to epinephrine in the ventricular tachycardia/ventricular fibrillation protocol. Vasopressin is an integral component of the hypothalamic-pituitary-adrenal axis and the neuroendocrine stress response. The recommended dose for an adult in fibrillatory arrest is 40 units in a single bolus. For vasodilatory shock states associated with sepsis, hepatic failure, or vasomotor paralysis after cardiopulmonary bypass, infusion at a rate of 0.01 to 0.04 units/min may be particularly useful. Vasopressin is neither recommended nor forbidden in cases of pulseless electrical activity or asystolic arrest, and it may be substituted for epinephrine. ACS Surgery: Principles and Practice 3 PERIOPERATIVE CONSIDERATIONS FOR ANESTHESIA — 17 Table 16 Cardiac Conditions Associated with Risk of Adverse Outcome from Endocarditis for Which Prophylaxis Is Reasonable67 Prosthetic cardiac valve or prosthetic material used for cardiac valve repair Previous infective endocarditis Congenital heart disease (CHD)* Unrepaired cyanotic CHD, including palliative shunts and conduits Completely repaired congenital heart defect with prosthetic material or device, whether placed by surgery or by catheter intervention, during the first 6 months after the procedure† Repaired CHD with residual defects at the site or adjacent to the site of a prosthetic patch or prosthetic device (which inhibit endothelialization) Cardiac transplant recipients who develop cardiac valvulopathy *Except for the conditions listed above, antibiotic prophylaxis is no longer recommended for any other form of CHD. † Prophylaxis is reasonable because endothelialization of prosthetic material occurs within 6 months after the procedure. antibiotic prophylaxis Recently, the Americal Heart Association has revised the guidelines for administration of antiobiotic drugs prophylactically to prevent infective endocarditis.67 Infective endocarditis prophylaxis is no longer recommended for mitral valve prolapse or for the stenotic or regurgitant cardiac lesions associated with rheumatic heart disease [see Table 16]. A suggested antibiotic regimen is provided in Table 17. Table 17 Antibiotic Protocol67 Situation Agent Regimen: Single Dose 30–60 min before Procedure Adults Children Oral Amoxicillin 2g 50 mg/kg Unable to take oral medication Ampicillin or cefazolin or ceftriaxone 2 g IM or IV 50 mg/kg IM or IV 1 g IM or IV 50 mg/kg IM or IV Allergic to Cephalexin*† or clindamycin or penicillins or azithromycin or ampicillin clarithromycin oral 2g 600 mg 500 mg Allergic to Cefazolin or penicillins or ceftriaxone† or ampicillin clindamycin and unable to take oral medication 1 g IM or IV 50 mg/kg IM or IV 600 mg IM 20 mg/kg or IV IM or IV 50 mg/kg 20 mg/kg 15 mg/kg IM = intramuscular; IV = intravenous. *Or other first- or second-generation oral cephalosporin in equivalent adult or pediatric dosage. † Cephalosporins should not be used in a person with a history of anaphylaxis, angioedema, or urticaria with penicillins or ampicillin. References 1. Barash PG, Cullen BF, Stoelting RK, editors. 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Philadelphia: Lippincott Williams & Wilkins; 1999. p. 385. 88. Canadian Pharmacists Association. Compendium of pharmaceuticals and specialties. Toronto: Webcom Limited; 2007. 89. Koblin DD. Mechanisms of action. In: Miller RD, editor. Miller’s anesthesia. 6th ed. Philadelphia: Elsevier Churchill Livingstone; 2005. p. 105. 90. Eger EE II. Uptake and distribution. In: Miller RD, editor. Miller’s anesthesia. 6th ed. Philadelphia: Elsevier Churchill Livingstone; 2005. p. 131. 91. Naguib M, Lien CA. Pharmacology of muscle relaxants and their antagonists. In: Miller RD, editor. Miller’s anesthesia. 6th ed. Philadelphia: Elsevier Churchill Livingstone; 2005. p. 481. Acknowledgment Financial disclosure: none reported. 11/08
