Chapter 7. The Anesthetic Plan for Healthy Patients

1. The main objectives in anesthetizing healthy patients are safety and efficacy.

2. The purpose of the anesthetic history and physical examination in healthy patients is 4-fold:

   • To elucidate the nature of the surgical problem and the specific requirements of the planned operation
   • To ensure that the patient is, in fact, healthy
   • To identify patient features that could complicate the anesthetic
   • To ascertain and document patient expectations and preferences

3. A successful anesthetic plan must take into account the needs of the patient, the surgeon, and the anesthesiologist.

4. Healthy patients can undergo most of their preoperative evaluation and preparation immediately before surgery.

5. Extensive evaluation and testing are rarely necessary in healthy patients undergoing uncomplicated surgical procedures.

6. Anesthetic monitoring has evolved greatly and is believed to prevent complications and improve outcomes.

7. Healthy patients rarely require more than basic, noninvasive monitoring.

8. Healthy patients occasionally undergo complicated surgical procedures that require additional and more invasive monitoring.

Like their medically ill counterparts, healthy patients undergo a variety of surgical procedures. By virtue of their favorable physical status, however, healthy patients generally undergo shorter and simpler operations. This is fortunate because surgical complexity is one contributor to perioperative risk. Healthy patients, by definition, are free of medical comorbidity, which is another contributor to perioperative risk. For purposes of this chapter, "healthy" patients are defined as American Society of Anesthesiologists1 (ASA) class I or II. Despite the fact that perioperative risk is low in healthy patients, development of an anesthetic plan is largely the same as that for patients with serious comorbidities. Successful development of this plan consists of several important steps. The first is a thorough evaluation of the patient via history and physical examination. In healthy patients, a key component of this evaluation is the history of perioperative, and specifically anesthetic, problems and complications. A successful plan must also take into account any special considerations that may be associated with the proposed surgical procedure. Finally, expectations and needs of both patient and surgeon must be taken into consideration. Of these, safety and efficacy are of utmost importance. This chapter reviews the evaluative phase of the anesthetic plan, with special focus on recognition and avoidance of complications that can occur in healthy patients. Focus is then placed on the derivation of a safe and efficacious anesthetic plan that will meet the needs of both patient and surgeon. Finally, we review the use of routine and special monitors in healthy patients undergoing elective operations.

History

Formulating an anesthetic plan begins with a thorough evaluation of the patient. The starting point for this evaluation is the complete history and physical examination. In October 2001, the ASA published a Practice Advisory for Preanesthesia Evaluation.2 This advisory provides guidelines regarding minimum requirements for the history, physical examination, testing, and timing of the preoperative assessment. Throughout this chapter we invoke principles of this advisory when specific issues relate to the healthy patient.

In the context of the healthy patient, the purpose of the history and physical examination is 4-fold:

• To fully elucidate the nature of the proposed operation and the problem for which the operation is being performed
• To ascertain the presence or absence of comorbidities or conditions that can heighten perioperative risk (to verify that the patient is, in fact, healthy)
• To ascertain whether the patient has a history of perioperative complications
• To educate the patient and then devise a plan that takes into account his or her preferences

The preoperative history and physical examination is typically a joint effort between the surgeon and the anesthesiologist. Following are specific goals and methods for the conduct of such a preoperative history and physical examination, which are well summarized in the ASA Practice Advisory for Preoperative Evaluation.2

Type of Surgical Disease and Planned Surgical Procedure

In planning an anesthetic, the primary goals of the anesthesiologist are patient safety and satisfaction, and the provision of ideal operating conditions. The starting point for development of this plan is a thorough understanding of the surgical problem. The physical problem that necessitates operation can often have a significant impact on the provision of safe anesthesia. For example, patients presenting for surgical correction of temporomandibular joint disease may have significant issues with airway management. In addition, operations that achieve the same end point are often performed using different approaches and techniques. For example, otherwise healthy men may undergo prostatectomy using either a laparoscopic or an open approach. Surgical technique alone can alter the anesthetic choice.

Much information regarding the surgical condition and planned procedure is obtained from the surgical history and physical examination, which is performed by the surgeon or a clinical "extender" of the surgeon (physician assistant, resident, nurse practitioner). It is critical that effective communication be maintained between members of the surgical and anesthesia teams to develop an optimal anesthetic plan. Computerized medical records aid greatly in achieving this goal. Most healthy patients do not require an anesthetic evaluation in advance of their operation. However, the surgical team must recognize when an advance visit with an anesthesiologist is appropriate, ensuring that such visits occur when indicated. To this end, preoperative anesthesia assessment clinics have evolved, along with screening criteria to aid surgical teams in deciding who needs this consultation. Preoperative clinics are discussed in subsequent sections.

Defining "Healthy"

"Healthy" patients are considered to be ASA physical status classification I and II.3 By definition, these patients either have no disease or have minor disease processes that are well controlled and cause no physical limitation. Menke and colleagues demonstrated in 1993 that ASA classification independently predicted overall perioperative risk and that this risk was low in ASA I and II patients.4 Similar findings have been verified by other authors, and the classification is still in common use5 (Table 7-1).

After the surgical condition and the specifics of the operation have been clarified, the next goal of the anesthesia provider is verification that the patient is, in fact, free of disease. This constitutes the bulk of the preoperative history and physical in healthy patients, and it is a joint venture between surgical and anesthetic teams. A comprehensive review of systems is the method of choice for this purpose, which is generally obtained by a member of the surgical team. It is good practice for anesthesiologists to verify and further explore these findings when pertinent for provision of safe anesthesia. Assessment tools and guidelines are helpful for this purpose. The American College of Cardiology/American Heart Association guidelines are useful for patients with suspected cardiovascular disease.6 Similar guidelines exist for evaluation of the respiratory system. The review of systems is also a valuable tool for careful screening of other organ systems including the coagulation system.

Occasionally, findings from the review of systems (eg, history of gastroesophageal reflux disease, neuropsychiatric disorders, clotting abnormalities) can alter the anesthetic plan in otherwise "healthy" patients. In addition, medical disease (hypertension, diabetes, coronary artery disease, asthma, obstructive pulmonary disease, etc) is occasionally diagnosed in surgical patients previously assumed to be "healthy"; such patients may require further evaluation and treatment before operation. Communication with the referring surgeon is important because this evaluation and treatment can delay the planned procedure.

Identifying Potential Anesthetic Complications

Even patients who lack comorbidities may have a spectrum of potential anesthetic complications (Table 7-2).

In healthy patients, a primary determinant of the success of an anesthetic is avoidance of these complications. Hence a major focus of the anesthesiologist's medical history in healthy patients is identification of potential complications. Patients may have a personal or a family history of complications, and when such a history is elicited, the patient should always be asked to provide a thorough account of the events and their consequences. In addition, it is important to obtain the medical records if possible. Once the complication has been identified and elucidated, the anesthetic plan should be altered to minimize the risk of that complication recurring. This plan should be clearly documented and the patient informed that steps have been taken for prevention. Next is a discussion of common anesthetic complications and steps that can be taken to minimize or eliminate them.

Postoperative Nausea and Vomiting

The most common complication associated with anesthesia is postoperative nausea and vomiting (PONV). This complication is highly distressing yet amenable to prevention.7 Recognition of this problem, followed by alteration in the anesthetic plan, has resulted in marked improvements in patient outcome and satisfaction.8 Untreated nausea occurs in as many as 40% of patients undergoing general anesthesia.9 Golembiewski's excellent review of this subject outlines patient characteristics that heighten risk (Table 7-3).

When these characteristics, or a strong history of PONV, are encountered, the anesthetic plan should include use of anesthetics with less likelihood of causing the disorder (eg, total intravenous anesthesia [TIVA] with propofol).8 In addition, strong consideration should be given to prophylactic use of antiemetic drugs that are highly effective.8 The PONV algorithms used at the University of Michigan are illustrated in Figs. 7-1 and 7-2. Note that, after induction, droperidol (0.625 mg intravenously [IV]) is included as a primary prophylactic agent in high-risk patients. The US Food and Drug Administration (FDA) has placed a "black box" warning on droperidol, given its propensity to prolong the QT interval, which may be associated with serious cardiac rhythm disturbances.10 Subsequent investigations have challenged this measure, citing remarkable safety at typical dosages used in modern anesthetic practice.11 It is therefore controversial whether there should be a limit on the use of droperidol, given its track record of safety and efficacy.

Finally, anxiety as a possible causative factor can often be effectively addressed by a frank acknowledgment to the patient that the problem has been recognized and that steps are in place for prevention.

History of Difficult Airway

When difficult airway management is known or suspected, a thorough account of the findings and management must be sought from both patient and old medical records. "Difficult airway" usually means that airway anatomy was such that standard laryngoscopy was either difficult or impossible. When this is identified in the preoperative history, subsequent management via an awake technique should be considered. Patients with difficult airways are often otherwise healthy, but this alone presents significant anesthetic risk. The prospect of awake airway management usually provokes anxiety. The possibility of awake intubation is best communicated well in advance of the operative date. Explanation of the plan in a slow, reassuring fashion serves to inform and prepare the patient and thus minimize anxiety on the day of operation. A brief overview of airway assessment follows in the physical examination section, but a full review is considered in greater detail in Chapter 36.

Malignant Hyperthermia

A rare anesthetic complication that must be recognized and planned for is malignant hyperthermia (MH). Estimates of the incidence of this complication range from 1 in 20000 to 1 in 70000.17 Recognition, prevention, and treatment of MH have been a major success story in anesthesia. (See Chapter 87 for an in-depth review of MH; it is considered only briefly here, but detailed knowledge is required by all anesthesia practitioners.) Patients with potential MH risk must be seen well in advance of operation so that a complete clinical history is obtained and a plan of care can be devised and communicated to the patient and other providers.

Nearly uniformly fatal in the past, this disorder now has a mortality rate of less than 10%.19 When patients present with either a personal or family history of the disorder, the anesthesiologist is confronted with decisions regarding testing and perioperative management. Muscle biopsy testing for the disorder is available at a diminishing number of centers and is costly, time consuming, and not completely reliable.20 Although genetic testing appears promising, it is not widely available currently. Many anesthesiologists therefore proceed with the assumption that the patient is at risk and provide a nontriggering anesthetic. In some cases, regional anesthesia or conscious sedation may be appropriate. In others where these are not appropriate, a nontriggering general anesthetic is provided. Bryson et al demonstrated recently that even general anesthesia could be safely provided to MH susceptible outpatients, as long as "triggers" were avoided.21 "Nontriggering" in this sense means avoidance of the only 2 reliable MH triggers: succinylcholine and potent inhaled anesthetics. This is typically accomplished with TIVA (see Chapter 43), which includes propofol, nondepolarizing neuromuscular blocking agents, and opiates. A minimum of 4 hours of observation are recommended following an uneventful anesthetic.22

Pseudocholinesterase Deficiency

Pseudocholinesterase (butyrylcholinesterase) is a plasma enzyme with no known physiologic function. Deficiency of this enzyme is attributable to alterations in the gene that codes for it. In 2003 Yen and colleagues estimated the incidence of homozygous (affected) individuals to be approximately 1 in 1800.23 Deficiency is usually identified when an anesthetized patient has prolonged recovery from the depolarizing neuromuscular blocking agent succinylcholine. Suspicion of this deficiency first arose in 1953 when Nilsson gave a patient succinylcholine, who then failed to resume spontaneous ventilation after completion of a short operation,24 hence the colloquial name "suxamethonium apnea." Mivacurium, a short-acting nondepolarizing neuromuscular blocking agent, has also been shown to depend on this enzyme for elimination.25 Despite being far more common than its inherited counterpart MH, pseudocholinesterase deficiency poses far less danger to patients. In addition, testing for the disorder is far simpler and more widely available than that for MH. Once identified, safe management entails ventilatory support combined with sedation until the drug is eliminated via the kidney (after several hours in homozygous recessive patients). Identification of this condition in advance allows for alteration of the anesthetic plan so that use of these drugs can be avoided. (More extensive review of MH is provided in Chapter 87.)

Awareness

There has been growing public concern about intraoperative awareness and so-called awake paralysis, leading to increased anxiety in patients undergoing general anesthesia. Unfortunately, the true incidence of intraoperative awareness under general anesthesia, reported to range from 0.2% to 1.0%, is probably underestimated15 because not all patients who are aware in the operating room remember the fact afterward. This can be a particularly bothersome experience for many patients, and lasting adverse sequelae are common.26 Domino and colleagues, using analysis of litigation records, identified awareness as a common root cause for legal action against anesthesiologists.27

As with other complications, a thorough account of the events from both the patient and their records should be sought. Occasionally, patients misinterpret the goals of conscious sedation and label this as intraoperative awareness. It is important to clarify this distinction to patients preoperatively, so that expectations are realistic. In light of the recent focus on intraoperative awareness, the Bispectral Index Sensor (BIS) monitor has evolved.28 Although use of BIS monitoring may reduce the incidence of awareness, recent reports by Mychaskiw and Rampersad cast doubt on this technology. Both demonstrated awareness despite BIS values that were maintained in the "anesthetized" (low value) range.29,30 Use of this device is reviewed more thoroughly in the monitoring section that follows. Whenever strong suspicion of awareness under general anesthesia exists, plans must be made to alter the anesthetic to prevent recurrence. In his concise review, Kazanjian outlines several methods to reduce the incidence of awareness and provides steps to respond to this complication31 (Table 7-4).

Recent ASA guidelines on intraoperative awareness and brain function monitoring also provide clinicians with useful information for evaluation and treatment plans to prevent this worrisome complication.32 These include careful preoperative evaluation because certain patient features such as drug resistance may be predictive.27 In addition, various types of surgery (cardiac, obstetric, trauma) as well as anesthetic techniques may place patients at particular risk.33 The ASA recognizes that processed electroencephalogram (EEG) devices, which assign a numeric value to a patient's level of sedation, are marketed to minimize the risk of intraoperative awareness, and they state, "We are interested in following their continued evolution and in conducting further research in this area." Hence the ASA concludes, "Brain function monitors are an option to be used when the anesthesiologist deems it appropriate, just as he or she makes choices about specific drugs, dosages, warming devices, and other types of monitors depending on the individual patient."

Additional Complications

Additional perioperative complications exist, and recognition of these complications is critical in preventing their reoccurrence. In a 2004 review, Mertes and Laxenaire found that serious drug reactions are surprisingly common in anesthetic practice,34 and in many cases alternative drugs can be selected (antibiotics, local anesthetics, opiates, others) or avoided altogether (succinylcholine in the case of pseudocholinesterase deficiency). Pulmonary aspiration of acidic gastric contents has the potential to complicate any anesthetic, even in otherwise healthy patients. Gastroesophageal reflux disease (GERD) and a full stomach are potential risk factors in healthy patients. If general anesthesia is being contemplated when aspiration risk exists, the anesthetic plan is altered in two ways:

1. Prophylactic antiaspiration measures should be taken (gastric motility drugs, pharmacologic stomach acid reduction, and rapid sequence induction).

2. Laryngeal mask airway should not be used.

Finally, even in the absence of anticipated risks or complications, many patients simply have high anxiety levels. It is appropriate for these patients to visit with an anesthesiologist in advance of their operative date to address and ameliorate this anxiety. There is even evidence to suggest that nonpharmacologic strategies, such as psychological support or soothing music, may play a significant role in treating both pain and anxiety.35

Medication Review

A thorough drug history must be obtained from all patients undergoing elective surgery. Even healthy patients may take a variety of prescription and nonprescription medications. All medications must be recorded, and reasons for their use must be assessed. Patients must also be questioned carefully about drug allergies and intolerances, and clear a distinction between the two must be documented in the medical record. When obtaining a drug history, it is important to ask that all regularly ingested exogenous compounds, including over-the-counter medications, herbal preparations, and vitamin supplements, be reported. Several of these compounds have been associated with serious perioperative complications and drug interactions.36 Planning for a safe anesthetic usually entails discontinuation of many of these preparations well in advance of the planned procedure, which the ASA recommends.37 Table 7-5 contains a list of common herbal preparations and adverse interactions that have been associated with them.

Finally, it is important to determine whether patients are using illicit drugs because many of these drugs have also been associated with anesthetic complications.38 Patients must be advised to abstain from all forms of illicit drugs well in advance of an elective procedure.

Physical Examination

The purpose of the physical examination in healthy surgical patients is to corroborate and augment findings from the medical history. Thus the first goal of the physical examination is to rule out disease. The second goal is to identify physical features that may make provision of anesthesia difficult or potentially lead to complications. In actuality, the physical examination begins while the history is being obtained. This direct interaction is a good time to observe the gross physical appearance and mental status of the patient. It is also a good time to look for obvious skin (jaundice, cyanosis, signs of dehydration, rashes) or musculoskeletal abnormalities (especially spine deformities) that may give clues to underlying pathologic conditions. This examination begins with a set of vital signs, including room-air oxygen saturation. Even if previously documented from the surgical history and physical examination, it is important for anesthesiologists to perform baseline examinations of both the cardiovascular and respiratory systems before elective surgery. Finally, a meticulous examination of the airway must be performed to assess for features that predict difficult airway management if the need for general anesthesia should arise.

Vital Signs

Even in the presence of a negative medical history, abnormal vital signs can be an important first clue to the presence of underlying disease. In fact, potential medical risks such as hypertension and thyroid disease are occasionally diagnosed during the preoperative history and physical examination. The so-called white coat phenomenon is responsible for hypertension in many preoperative patients.39 Significant elevations in blood pressure or heart rate, however, especially on repeated measures, warrant further investigation and possible therapy. Rather than simply asking, height and weight should be accurately measured. Arterial blood pressure should be determined either via sphygmomanometry or oscillometry, using an appropriate-size cuff. It is desirable to obtain blood pressure in both arms. We feel strongly that baseline room-air oxygen saturation should be measured via pulse oximetry in every patient.

Cardiorespiratory Examination

Examination of cardiovascular and respiratory systems also begins with observation of the patient, which is conveniently accomplished while obtaining the history. Findings such as labored breathing, wheezing, coughing, clubbing of the nails, jugular venous distention, and cyanosis are typically identified while simply conversing with a patient. Obviously, these are signs of potentially serious pathologic conditions and should be investigated further by more in-depth examination. Physical examination of the cardiovascular system aids in ruling out hypertension, valvular heart disease, and heart failure. Palpation and auscultation of the heart should be performed to identify heaves, rubs, extra heart sounds, and murmurs. Peripheral pulses should be assessed for both quality and magnitude. The chest should be examined for wheezes, rales, and rhonchi.

Airway Evaluation

Regardless of the anesthetic chosen for a particular operation, it is important that careful examination of the airway be performed in every patient. Although much of the remainder of the physical examination represents a combined or even redundant effort between anesthesiologists, surgeons, and internists, a complete airway evaluation is generally not the purview of other medical specialists. The anesthesiologist is solely responsible for securing the airway and establishing ventilation. Difficulty with these processes may place the patient in great peril. This is borne out by the fact that airway management problems account for a relatively large proportion of anesthesia-related morbidity and mortality. In ASA closed claims analyses, both Caplan et al and Domino et al demonstrated that loss of the airway is a frequent cause of litigation associated with severe injury or death.40,41 If a patient is known to have a difficult airway, alternative management plans are available (eg, awake fiberoptic intubation). Identifying patients with difficult airways, followed by these alternative induction techniques, should eliminate the "unconscious patient, can't intubate, can't ventilate" scenario. It is therefore a major goal of anesthesiologists to predict the potentially difficult airway in advance of anesthetic induction.

Tests to Predict Difficult Laryngoscopy

Preoperative airway assessment, with the aim of detecting and thus anticipating the difficult airway, has evolved over the years. Currently, a number of strategies exist for systematic evaluation of the airway, and various guidelines endorse the use of such strategies.48 Key elements of the airway examination include neck anatomy, neck flexion and extension, thyromental distance, mouth opening, Mallampati score, and, more recently, jaw protrusion and the presence of a beard. Excellent reviews are available on the various tests and strategies commonly used by anesthesiologists to assess physical and symptomatic features that may predict difficult laryngoscopy49 (Table 7-6).

Mandibular displacement (upper lip bite test) was correlated with the difficulty of laryngoscopy and may have clinical utility.43 Although these various tests and maneuvers are simple to perform, they have questionable sensitivity and specificity, and hence unreliable predictive value.14 This explains the occasional finding of the "unanticipated difficult airway" after seemingly reliable testing preoperatively predicted otherwise.14 Typically, the goal of these tests is to correlate symptomatic (eg, sleep apnea) and anatomic patient features with difficult laryngoscopy.49

Difficult Mask Ventilation

Although successful laryngoscopy followed by endotracheal intubation constitutes definitive management for an unconscious and apneic patient, ventilation by mask can be a lifesaving maneuver. Despite this fact, the historical precedent for investigators with an interest in predicting the difficult airway has been to focus on laryngoscopy alone. Given the potentially lifesaving importance of mask ventilation, however, investigators have begun to stress both laryngoscopy and mask ventilation in their predictive strategies. Langeron and colleagues, in 2000, estimated the incidence of difficult mask ventilation and identified several predictive physical features: history of snoring, body mass index (BMI) higher than 26, lack of teeth, age older than 55 years, and beard.42 In 2004 Han et al devised a scale for categorizing the difficulty of mask ventilation. This 4-point scale elaborates on the work by Langeron, who only noted difficult and impossible ventilation. In contrast, the Han scale describes four degrees of assessment of ventilation, similar to scales used for laryngoscopy (Table 7-7).

Han et al found an incidence of difficult mask ventilation of 1.5% in the 3000 patients they studied.50 More recently, a study of more than 41,000 patients confirmed the incidence of difficult ventilation to be approximately 1.5% and that the incidence of impossible ventilation was 0.5%.51 This large study by Kheterpal et al found 6 independent predictors (4 of Langeron's) of difficult mask ventilation: history of snoring, age older than 58 years, BMI higher than 30, Mallampati class III or IV, limited jaw protrusion, and the presence of a beard (Table 7-8).

Of these, the only modifiable risk factor is the presence of a beard. This suggests that anesthesiologists should consider recommending that patients shave prior to elective procedures if they possess other risk factors for difficult mask ventilation. Table 7-9 illustrates the standard preoperative airway features that we assess and record via electronic data entry at the University of Michigan.

Anticipated Difficult Airway Strategy

When a potential difficult airway is identified, it is the anesthesiologist's responsibility to develop a management strategy, in the event that general anesthesia becomes necessary. When a truly difficult airway is known or strongly suspected, and general anesthesia is necessary, the usual management plan entails placement of an oral or nasal endotracheal tube while the patient is awake and spontaneously breathing. Techniques for awake endotracheal intubation are reviewed in Chapter 36. Several important steps in planning and patient preparation, however, are worth mentioning.

The very thought of a potential airway problem can be anxiety provoking. The source of this anxiety often stems from patients' perception that theirs is a rare problem that places them in danger. To allay this anxiety, it is helpful to have a frank discussion with patients to fully inform them about the nature of the problem, and the rationale and plan for safely dealing with it. Patients are reassured knowing that the difficult airway is relatively common and that appropriate management poses no untoward danger. Careful anxiolytic sedation is appropriate preoperatively, to the extent that airway compromise is avoided. Antisialagogue premedication (typically glycopyrrolate 0.4-0.6 mg IV) aids greatly in the ability to anesthetize airway mucosa (typically with 2%-4% lidocaine). Profound topical anesthesias of upper airway mucosa, combined with judicious sedation, are the key elements in conducting a safe, effective, and comfortable awake intubation.

Special Preoperative Considerations

Preoperative Anesthesia Assessment Clinics

Currently, the vast majority of patients presenting for elective surgery present to the hospital on the day of their procedure. Fortunately, most healthy patients can be seen and assessed by the anesthesia team immediately before their operation. The ASA Practice Advisory on Preanesthesia Evaluation recommends that timing of the preoperative evaluation be based not only on the health of the patient but also the invasiveness of the surgical procedure.52 They recommend that all patients undergoing highly invasive surgical procedures be seen before the day of surgery. These patients require evaluation, counseling, and possibly therapy in advance of their surgical date. An appropriate and convenient place to coordinate this workup is the preoperative anesthesia assessment clinic (PAC). To derive the most benefit from PACs, surgeons need to use them discriminately. We find it helpful to provide screening criteria to our surgeons in the form of a patient self-assessment sheet.53 This screening questionnaire is filled out by the patient using a series of checkboxes. The boxes are aligned to a back page such that positive answers will check (via carbon copy) the recommended preoperative laboratories and whether a PAC consultation is suggested. For example, if an affirmative answer is recorded for the question "Do you have heart disease?" an electrocardiogram is ordered (if not recently done) and the patient may be referred for further evaluation (Table 7-10).

Obesity and Obstructive Sleep Apnea

Obesity is a well-established public health problem in developed countries. More specifically, obesity presents a major problem for practitioners who care for patients in the perioperative period. Obese patients have alterations in physiology at baseline that result in major lifestyle limitations, but they also have a well-documented increase in perioperative risk.54 This would seem to justify an ASA Physical Status classification of at least II, and perhaps III. Multiple physiologic comorbidities exist in obese patients (diabetes mellitus, obstructive sleep apnea [OSA], cardiovascular disease, osteoarthritis, and others).55 In addition, anatomic alterations of the airway also place these patients at increased risk for difficult mask ventilation and laryngoscopy.53 IV access can be extremely difficult in obese patients, and in some cases central access must be considered. Some consider obesity a risk factor for gastric aspiration, and preventive measures should be considered. Obesity clearly heightens risk for adverse perioperative respiratory outcomes.56 Blum et al reviewed the quality assurance events recorded from 25767 anesthetics. They found a statistically significant increase in failed intubation, reintubation, dental injury, and airway obstruction associated with increasing BMI.54

Short of substantial weight loss prior to elective surgery (which has a dismal success rate), the perioperative risks just listed generally are not modifiable. Hence a key element for practitioners to consider in preparation for elective operation in obese patients is counseling, specifically with regard to weight loss (if time permits) and full disclosure of significantly heightened perioperative risks.57

It may also be beneficial to prepare obese patients for practical issues such as difficult IV access and the possible need for awake intubation. OSA is a syndrome commonly associated with obesity and is characterized by periodic, partial, or complete airway obstruction during sleep. It is estimated that approximately 9% of women and 24% of men have some degree of OSA; severe symptomatic disease is present in approximately 2% of women and 4% of men.58 In October 2005 the ASA published a practice guideline, "Perioperative Management of Patients With Obstructive Sleep Apnea." This practice guideline comprehensively reviews the preoperative and postoperative management of patients with this disorder.59 On occasion, patients who are considered to be healthy may have undiagnosed OSA, and therefore it is important to get a complete history, specifically as it relates to snoring and daytime somnolence. If the patient is indeed suspected of having the syndrome, then they should be evaluated before an elective procedure as recommended by the practice guideline.

Old Age

The US population is aging rapidly, and an increasing proportion of surgical procedures are performed in the elderly. In 1986 Tiret et al provided evidence that the elderly have higher perioperative complication rates and higher risk than their younger counterparts, even in the absence of comorbidities.60 The issue of perioperative risk, as it relates solely to advancing age, however, is far from settled.61 Some would therefore assert that anesthetizing "healthy" elderly patients poses no significant elevation in perioperative risk. But even "healthy" elderly patients may have marked diminution in the function of major organ systems.62 This would cause some to assign the ASA classification of II or even III to all such patients. Aside from the universal physiologic changes seen in all elderly patients ("aging"), elderly patients definitely tend to accumulate coexisting disease. Importantly, Kim and colleagues clearly demonstrated that coexisting disease in the elderly is a strong predictor of complications.63 Elderly patients often have additional and unique perioperative challenges. Many have poor hearing and eyesight, and some suffer from cognitive impairment. This can make communication difficult. Simple issues like transportation home after conscious sedation can become logistical problems in the elderly. Another important effect of aging is altered drug disposition. Elderly patients have diminished volumes of distribution, decreased clearance, and heightened sensitivity to nearly all medications. This explains why elderly patients are more sensitive to the therapeutic actions of most drugs and markedly more susceptible to side effects. In summary, despite changes attributable to normal aging, there is no strong association between age itself and perioperative risk. Thus chronologic age per se should not be a contraindication to surgery. Finally, to avoid complications and dissatisfaction in the elderly, anesthesia providers need to understand the altered pharmacology, physiology, and special needs that accompany the normal aging process.

Smoking

Approximately one in five adult Americans currently smoke, and millions of elective surgical procedures are performed each year on these individuals. This is unfortunate because cigarette smoking is independently responsible for an alarming increase in the rate of perioperative pulmonary complications.64 Cigarette smoking is an addictive disease that adversely alters the lifestyle of those affected. This fact, coupled with the well-known perioperative risks that smoking confers,65 should result in otherwise healthy smokers being classified as at least ASA II and, in many cases, ASA III. A 2000 US Public Health Service guideline advised all physicians to "strongly advise every patient who smokes to quit because evidence shows that physician advice to quit smoking increases abstinence rates."66 Further, anesthesiologists are uniquely positioned to give such advice. The preoperative interaction has been described by Warner as a "teachable moment" that not only lowers immediate perioperative risk but is also of great benefit to the long-term health of smokers.67 Quitting smoking immediately before surgery has not been shown to heighten risk, produce untoward anxiety, or consistently precipitate nicotine withdrawl.68 Hence patients who smoke should not be considered "healthy." These patients should be advised of the elevation in perioperative risk that is attributable to their habit and be encouraged to quit as soon as possible before their elective surgical procedure.

Preoperative Testing in Healthy Patients

Billions of dollars are wasted in the United States each year on unnecessary preoperative testing.69 In the case of healthy patients, this testing is almost always unnecessary.70 It is generally accepted that healthy patients undergoing low-risk surgical procedures require no specific laboratory testing unless clinically indicated.71 Little evidence exists regarding the propriety of such routine testing in healthy patients undergoing more complicated procedures with the potential for major blood loss (eg, major corrective orthopedic procedures, brain aneurysm clipping). Many recommend obtaining a preoperative hematocrit level in menstruating women, but there is little evidence to support this.72 Women of childbearing age should be given pregnancy tests if it cannot be ascertained for certain whether or not they are pregnant. It is our institutional policy that women 18 years of age and older be asked, "Is it possible that you could be pregnant?" If they answer "no," they are not tested. This is in general agreement with the ASA stance on this issue: "The task force believes that the literature is inadequate to inform patients or physicians on whether anesthesia causes harmful effects on early pregnancy. Pregnancy testing may be offered to female patients of childbearing age and for whom the result would alter the patient's management."54

The indiscriminate ordering of batteries of routine tests, even in patients with serious comorbidity, has been the subject of intense recent review and been found to be excessively expensive and ineffective.31 In fact, batteries of routine tests and their subsequent interpretations were found to predict morbidity more poorly than simple use of either the ASA physical status classification or the ACC/AHA6 guidelines. The ASA Practice Advisory recommends that "specific tests and their timing should be individualized and based upon information obtained from sources such as the patient's medical record, interview, physical examination, and the types and invasiveness of the planned procedure."54 These concepts were well summarized by Halaszynski et al, in their 2004 article addressing this issue31 (see Table 7-11).

They suggest that age be used as a basic criterion for testing, with the additional components of surgical complexity and medical illness allowing for layers of flexibility. According to this paradigm, healthy patients younger than 45 years having uncomplicated operations require no testing. As patients deviate from this healthy/uncomplicated baseline, testing may be indicated but in a directed and temporally related fashion (if a test has been done recently, it does not generally need to be repeated). Thus if it can be ascertained from a history and physical examination that a patient is healthy, "routine" testing is rarely indicated in patients having uncomplicated surgical procedures. Age-based thresholds (men >45 years, women >55 years) for obtaining preoperative ECGs were recently called into question due to their arbitrary nature and unsatisfactory yield.73

Type of Anesthesia: General, Regional, Monitored Anesthesia Care

Once the goals of medical evaluation and preoperative preparation have been accomplished, the anesthesiologist and patient must devise an anesthetic plan. This is where surgeon requirements and patient preference directly interface. Surgeon requirements vary widely, but most patients simply want their surgical experience to be safe and comfortable. Surgeons want the best conditions possible to perform their operations. It is advisable that surgeons and anesthesiologists communicate in advance to express their requirements and limitations. Anesthesiologists have direct control over many variables that surgeons require to carry out their operations safely and swiftly: degree of consciousness, blood pressure control, ventilatory control, level of consciousness at the conclusion of surgery, and so on. If other factors are equal (patient has no particular preference, perceived safety is equal), surgeon preference must be taken into consideration. Patient safety is always of paramount importance. At times this issue may outweigh surgeon preference (eg, providing a regional anesthetic for lower extremity surgery in a patient with severe pulmonary disease).

Keeping safety in mind, the anesthetic choice is often influenced by two key patient features: coexisting disease and aging. A completely acceptable technique for a particular operation (eg, a subarachnoid block for a total knee arthroplasty) may be contraindicated in patients presenting with certain disease states (aortic stenosis). Whereas general anesthesia is performed rather indiscriminately in young healthy patients, regional or even local anesthesia with sedation may be the safest option in patients with severe respiratory disease. The same holds true for the elderly patient. Even "healthy" elderly patients have well-documented diminutions in the function of renal, hepatic, cardiorespiratory, and drug-metabolizing systems,62 and these changes are progressive. Drugs and doses that are innocuous in young healthy patients can have lasting and debilitating effects in the elderly. It is therefore desirable, whenever possible, to consider regional or even local anesthetics with minimal sedation in the elderly.

Type and location of surgery play an important role in planning for anesthesia, but patient preference and the destination of the patient in the postoperative phase also must be considered. Newer, more rapidly eliminated anesthetics have made postoperative destination less of an issue than in times past but one that still must be considered. For example, long-lasting regional blocks and long-acting IV medications may be inappropriate for patients scheduled on an outpatient basis. Following is an overview of common surgical operations and factors that influence the anesthetic plan.

Head and Neck Procedures

Head and neck procedures range from minor, superficial operations to complex resections and reconstructions involving nerve monitoring, fluid shifts, and major blood loss. Many simple superficial operations are performed for skin cancer excision, followed by closure of the defect. Unless these lesions are deep or large, the cases can usually be safely and comfortably managed with conscious sedation combined with local anesthetic applied by the surgeon. Unless brief and superficial, ear surgery usually necessitates general anesthesia to achieve suitable patient comfort. It is common for these procedures to be performed on an outpatient basis. Cosmetic facial surgery is often performed with conscious sedation combined with local anesthesia to preserve awake muscle tone. Complex head and neck operations are often performed for invasive (mouth, throat, neck) cancers. These operations can be very complex and involve much fluid shifting and blood loss. In addition, these lesions can compromise the airway, necessitating nonstandard (awake) airway management techniques. Presence of a tracheostomy is common at completion of these operations. Due to the duration and complexity of these procedures, invasive monitoring (eg, intra-arterial catheter) is common. Communication with the patient and family is important in achieving realistic expectations.

On occasion, intracranial neurosurgery is performed in the awake patient, but most craniotomies are performed under general endotracheal anesthesia. Anesthesia for awake craniotomy is beyond the scope of this chapter. Success in these cases depends on an intimate surgeon-patient-anesthesiologist interaction with much preoperative communication. Because operating conditions for intracranial operations depend on, and conversely, can have an impact on vasomotor control, invasive (particularly arterial) monitoring is common. Neurologic function (somatosensory evoked potentials) monitoring is common, and the anesthesiologist must be knowledgeable in the interactions of anesthetic agents and these monitors. Additionally, neurosurgeons often request (if feasible) that a rapid wakeup be accomplished at the conclusion of surgery so that early assessment of neurologic function can be carried out.

Thoracic Procedures

Thoracic surgical procedures range from outpatient thoracoscopic procedures (minor pulmonary resections and biopsies, sympathectomy) to major pulmonary and upper gastrointestinal tract procedures involving major body cavity and cardiovascular trespass, blood loss, and fluid shifting. Many of these procedures require single lung ventilation, which must be planned for. Open thoracic procedures are typically associated with a high degree of postoperative pain that is best controlled with epidural analgesia. Because of their proximity to major vascular structures and potential for adverse ventilatory interactions, these procedures often necessitate invasive intravascular lines and monitors that must be discussed with the patient as part of the preoperative plan.

Abdominal Procedures

Increasingly, abdominal procedures are being performed laparoscopically. General anesthesia with endotracheal intubation must be used for patients to tolerate this approach safely and comfortably. Regional techniques can be used successfully for open intra-abdominal procedures, but these operations are frequently long and complex, so general anesthesia is often favored. When general anesthesia is used, endotracheal intubation is indicated to provide abdominal muscle relaxation and to protect against gastric aspiration. Epidural is an excellent option for postoperative analgesia in open abdominal operations but is usually not necessary when procedures are performed laparoscopically. Because of the potential for vascular involvement, major blood loss, and fluid shifting, invasive monitors are sometimes indicated, even in otherwise healthy patients.

Urologic Procedures

Many urologic procedures are performed through a cystoscope and are of relatively short duration. In these cases, either short-acting regional or general anesthesia is an equally safe and effective option. Patient preference can play a major role in devising a plan for these cases. Both nephrectomy and prostatectomy have typically been performed via large open approaches, but they are increasingly being performed laparoscopically. Open prostatectomy has been performed successfully under both general and regional anesthesia, but the laparoscopic approaches for these procedures necessitate general anesthesia with endotracheal intubation.

Gynecologic Procedures

As with abdominal and urologic procedures, gynecologic procedures are being performed increasingly via the laparoscopic approach. The same principles previously mentioned for abdominal and urologic procedures apply. When performed via an open abdominal approach, gynecologic procedures generally require general anesthesia with endotracheal intubation to allow profound muscle relaxation. Vaginal, cervical, and hysteroscopic procedures can be completed safely and comfortably using either general or regional anesthesia. Thus patient preference combined with anesthetist experience must be taken into account when planning for these cases.

Orthopedic Procedures

At one extreme, orthopedic operations can be brief and minor peripheral extremity procedures amenable to either regional or local anesthesia with sedation. At the other end of the spectrum are long, complicated procedures involving blood loss, fluid shifting, and intraoperative nerve monitoring. Total knee and hip joint replacement operations are very common and can be carried out with either general or regional anesthesia. Epidural anesthesia is an effective choice and can be continued into the postoperative period to provide excellent analgesia. Some patients are extremely anxious about the prospect of being awake during orthopedic procedures. Consideration must be given to general anesthesia in these patients. Major spine surgery, operations for orthopedic malignancies, and revision hip operations can be long and complex, so general anesthesia with endotracheal intubation and invasive monitoring should be considered. Upper extremity nerve blocks are increasingly common for procedures on the shoulder and arm. Interscalene blocks and catheters are useful for shoulder surgery. Infraclavicular blocks and/or catheters are useful for procedures on the forearm and hand. Use of these techniques is discussed in Chapter 49. Because of the significant pain associated with shoulder reconstructive surgery and the need for postoperative manipulation for rehabilitation, interscalene catheters have become popular. These blocks have proven efficacy in the successful treatment of immediate postoperative pain.74

Ocular Procedures

Many surgical procedures on the eye can be carried out safely and comfortably using local anesthesia. When formulating the preoperative anesthetic plan, this technique must be fully explained so that the patient has realistic expectations. Some ocular procedures can be very long in duration and hence necessitate use of general anesthesia to provide optimal operating conditions. In these cases plans may need to be devised for "deep" extubation to avoid coughing and elevation of intraocular pressure upon emergence from anesthesia.

Regional Anesthesia versus General Anesthesia

The superiority of general anesthesia versus regional anesthesia for major surgical operations is controversial. Both techniques have advocates and detractors from both a safety and efficacy standpoint (see Chapter 46).

Although there is no convincing evidence that morbidity and mortality are decreased with either technique, there is a suggestion of improvement in specific outcomes with use of regional anesthesia.75 Despite the common perception that regional anesthesia is generally safer than general anesthesia, its principal advantage is in providing analgesia postoperatively. For certain operations, regional anesthesia offers distinct advantages compared with general anesthesia,76 but some of the perceived benefits of regional anesthesia have recently been called into question.77 For regional techniques to be successful, the patient must be accepting of the technique, a skilled clinician must be available to perform it, and the block must be effective. If long-lasting blocks or indwelling catheters are to be used, educational efforts must be made regarding the special care that these techniques require. Lastly, patients must be informed of the potential complications that can result from the use of regional anesthesia.

Monitored Anesthesia Care: Potential Pitfalls

Superficial operations and "noninvasive" (eg, cardiac electrophysiologic, endoscopic) procedures are commonly performed in healthy patients using the "monitored anesthesia care" (MAC) technique. This entails use of anxiolytic, sedating, and analgesic medications administered by anesthesia personnel, combined with local anesthesia administered by the surgeon. In a recent editorial, Hug describes the attitude of anesthesia providers regarding such cases as "routine, simple, and low-risk."78,79 In addition these operations are often performed hastily, in remote locations, and involve positioning that provides anesthetists poor access to the airway. This can result in a situation where "diligence is less by both the anesthetist and the surgeon."78 This, combined with liberal use of sedating respiratory depressant medications, has the potential to result in life-threatening anesthetic-related complications.

Complications attributable to MAC anesthesia have been reported in the literature, and a recent closed claims analysis by Bhanaker et al sheds new light on this devastating, yet uncommon problem. In this study, MAC anesthesia represented a "liability profile similar to claims associated with general anesthesia." This led the author to conclude that "oversedation leading to respiratory depression was an important mechanism of patient injury during MAC. Appropriate use of monitoring, vigilance and early resuscitation could have prevented many of these injuries."79 Hence anesthesia providers need to be cognizant of the potential for serious complications associated with MAC anesthesia and avoid the pitfall of trivializing this technique to the extent of compromised vigilance and potential serious complications.

Preoperative Instructions

A clear, concise set of preoperative instructions can contribute greatly to patient safety and operating room efficiency. Provision of these instructions can be carried out in a variety of ways, but we believe a combination of both verbal and written communication is most likely to achieve the desired result. At our institution the verbal communication is carried out in either the preoperative clinic or via a combination of surgical and nursing preoperative "teaching." Our written preoperative instructions are in the form of a folder or packet that is periodically reviewed by perioperative surgical, anesthesia, and nursing teams. The most important elements of preoperative instruction that relate to the provision of safe anesthesia are dietary (nothing by mouth [NPO]) and medication instructions. Fasting guidelines for elective surgery are clearly delineated by the ASA,80 and we tend to instruct patients conservatively (eg, interpreting "clear liquids" to mean "water").

ASA I and II patients may be taking a variety of prescription and nonprescription medications. To avoid potential complications, clear instructions must be given regarding continuation and avoidance of various medications before elective surgery. Medications that are typically continued include antireflux medications, cardiovascular and antihypertensive medications (with the possible exception of angiotensin-converting enzyme inhibitors and angiotensin receptor blockers),81 pain medications (with the possible exception of aspirin and nonsteroidal anti-inflammatory medications), psychotropic medications (with the exception of monoamine oxidase inhibitors), asthma medications, and antiseizure medications. Medications taken on the day of surgery should be consumed with as little water as possible. Alternative medications and herbal preparations deserve special consideration. Many patients do not consider these to be medications and hence must be specifically asked about their use. These products are poorly regulated and often contain unknown quantities of substances that can lead to serious perioperative drug interactions and complications.82 Because of the lack of data on many of these preparations, the ASA recommends that practitioners continually familiarize themselves with alternative medications, and it advises the discontinuation of all such products for at least 2 weeks before elective surgery.83

Premedication

It is difficult to find consensus on what constitutes the best plan for pharmacologic premedication before anesthesia. What is important is that each agent be administered only if there is a clear and specific indication for its use. The most common indications for preoperative administration of medications are anxiolysis, analgesia, gastric aspiration prophylaxis, surgical wound infection prophylaxis, and thromboembolic prophylaxis. None of these classes of medications should be administered on a purely routine basis. Each of these medications has a unique set of potentially dangerous side effects, including allergic reactions, drug–drug interactions, prolonged effects, and added cost. Hence in the absence of clear indications, healthy patients undergoing elective operations should receive little or no pharmacologic premedication.

Anxiety is common in patients undergoing even minor surgery, and it tends to heighten as the surgical event approaches. It is difficult to discern which patients will be anxious before surgery by any other means than a direct interview. Treating preoperative anxiety not only improves patient satisfaction84 but may have more far-reaching effects such as reduction in surgical stress response and lowering the incidence of PONV.85 Although the most commonly used agents used for this purpose are benzodiazepines, and particularly midazolam, other agents such as melatonin have proven to be safe and efficacious.86

Preoperative analgesia may be considered when painful conditions such as orthopedic fractures are present. If opiates are chosen for this purpose, patients must be monitored for sedative and respiratory depressant side effects. Some studies even support use of "preemptive analgesia" with agents such as ketorolac as a means to lower anesthetic requirements and their attendant side effects. Evaluation for the risk of nausea and vomiting were discussed previously. When this risk is identified, consideration should be given to single, or in select cases, multimodal therapy to prevent this complication. Healthy patients occasionally require thromboembolism prophylaxis in the perioperative period. This is most commonly accomplished with use of either low-dose or low-molecular-weight heparin preparations.

Postoperative Destination

The anesthetic plan must take into account the postoperative destination of the patient. Pre- and intraoperative planning must be flexible, so that safe and appropriate medical care is available if ongoing needs of the patient change. For example, many airway procedures can be accomplished on an outpatient basis. There is a relatively high risk with this type of surgery, however, that complications could require admission or even mechanical ventilation in an intensive care unit. This sort of eventuality must be taken into account for two reasons. First, operations with a relatively high likelihood of admission or intensive care unit management (even in otherwise healthy patients) should not be scheduled in facilities that lack the means to provide this care. Second, patients and their families must be advised beforehand of this possibility. Patients and family members must be aware that intraoperative events can change the postoperative destination of the patient, even if the initial plan was for same-day discharge.

Patients have three ultimate postoperative destinations: home, a hospital "floor" or "ward" bed, or the intensive care unit. A stay in the postanesthesia care unit (PACU, or "recovery room") may precede any one of these final destinations. Planning for the eventuality of any of these destinations must occur in both the pre- and intraoperative phases of an anesthetic. In the case of both the PACU and the intensive care unit, advance planning must be carried out so that a bed is available and the unit is appropriately staffed. Both patients and family members need to be made aware of the destination that was initially planned and of any changes that may have been made based on intraoperative (or PACU events). Fortunately, many procedures that are planned on an outpatient basis and are free of complications may entail very short PACU stays or (as is becoming increasingly common) bypass a recovery room altogether. This is generally safe, cost effective, and well received by patients but requires simple but crucial advance planning. For example, it is mandatory that patients who have received sedating medications have safe transportation home, usually in the person of a caregiver who can also assist with medication, surgical dressing issues, and other forms of assistance.

Postoperative Pain

Postoperative pain resulting from surgical procedures performed in healthy patients ranges from none to severe and relatively long lasting. As such, treatment of postoperative pain ranges from no treatment at one extreme (noninvasive endoscopic procedures) to invasive techniques including epidural analgesia and indwelling nerve plexus catheters. This section serves as a simple overview of available pain control options in healthy patients. See the comprehensive section on postoperative pain management in Chapter 72 for a more in-depth review of this subject. It is the anesthesiologist's responsibility to couple analgesia with hypnosis in the intraoperative phase and then continue some form of analgesia postoperatively while minimizing additional drug effects such as sedation and respiratory depression. A key feature in the success of this plan is education and physician-caregiver rapport in the preoperative phase. Although it is important for patients to wake up as pain free as possible, it is also critical that they be informed that they will likely experience some degree of postoperative pain. Realistic expectations regarding postoperative pain are a vital component in patient satisfaction and avoidance of complications related to pharmacologic control of pain.

As stated previously, healthy patients generally undergo short, simple surgical procedures. Occasionally, however, complicated operations are performed that result in severe postoperative pain. Thus the entire array of pain control modalities at the anesthesiologist's disposal must be available in this population. Despite controversy over its efficacy,87 preemptive analgesia with agents such as acetaminophen and nonsteroidal anti-inflammatory drug (NSAID) compounds should be considered. Use of these compounds is also typically the first line of therapy in patients having minor operations such as carpal tunnel repair or vasectomy. These compounds are generally devoid of side effects, but patients must be cautioned regarding overdose with resultant liver and kidney damage.

Opiates are indicated for moderate to severe pain via either oral or intravenous routes of administration. Patient-controlled analgesia (PCA) represents a major advance in the use of opiates for postoperative analgesia, but success with the technique depends on proper planning and patient instruction. Grass has recently reviewed this subject, including its history, safety, efficacy, and current practice guidelines.88 Major nerve conduction blockade (nerve blocks, plexus blocks) and epidural analgesia are occasionally necessary in healthy patients undergoing surgical procedures that will result in severe pain (eg, orthopedic procedures, intra-abdominal and pelvic procedures). Liu published an excellent practical review of indwelling catheters for postoperative pain relief.89 Although highly successful, both techniques are associated with potentially serious complications, and proper planning and consent requires disclosure of both aspects of these techniques. Finally, the issues of aging, opiate dependence, and abuse all have important implications for the successful planning and management of postoperative pain (see Chapter 72).

The medical community, the anesthesia community, and patients, to some extent, assume that monitoring during anesthesia and surgery results in fewer preventable mishaps and improved outcomes. Fortunately, since its introduction into modern medicine, anesthesia has become an increasingly safe proposition.90 As Domino and others continue to point out, however, rare anesthesia mishaps continue to have catastrophic outcomes (death, major morbidity) that are very costly to society.41 Every year, thousands of cases of death and serious morbidity are attributed solely to the provision of anesthesia.91 In a large proportion of these cases, the cause of the morbidity or mortality is believed to be preventable.92 Failure to prevent anesthetic catastrophes usually results from lapses in vigilance or simple human error. Anesthetic monitors are therefore intended to aid in the maintenance of vigilance and to alert providers to the possibility of human error. Following is an overview of monitors commonly used in healthy patients and the rationale for their use in various clinical scenarios. (See Chapters 30, 31, 32, 33, 34, and 35 for an in-depth review of monitoring.)

Despite the assumption that there is a correlation between monitoring and outcome, there is little in the way of scientific validation to support this assumption. Eichhorn and colleagues, in 1986, suggested that intraoperative monitors may reduce adverse events and therefore improve outcomes.93 From this body of work arose the ASA guidelines for intraoperative monitoring,94 which were recently amended (Table 7-12).

The assumption that monitoring improves outcome, coupled with anesthesia providers' zeal to gather information, can lead to practitioners erring on the side of more, rather than less monitoring devices. This would be ideal if monitors were cheap, completely accurate, and completely safe. Some modern monitoring devices, however, are expensive and do not always bring value. Some forms of monitoring have the potential to mislead anesthesia providers; others are even capable of causing serious physical harm.95,96 Therefore, in planning for an anesthetic, anesthesiologists must weigh the perceived advantages with the known potential for complications when choosing a monitoring strategy (Table 7-13).

Healthy patients having uncomplicated surgical procedures rarely need more than the ASA basic intraoperative monitors. Before considering machines that monitor the human body, however, it is vital that anesthesiologists maintain basic physical examination skills. These skills can give vital information about patients quickly and reliably. For example, failure of the chest to rise combined with a bubbling sound emanating from the patient's throat may indicate cuff failure or improper placement of an endotracheal tube. Tactile sensation of a bounding pulse, in the presence of a low machine reading, may indicate a problem with mechanical blood pressure measurement. Discoloration of a patient's skin combined with a feeling of warmth could be an early indicator of MH. Smelling a potent anesthetic vapor could be a sign of an airway leak or disconnect. Although it would be crude and unwise to rely solely on sense perception to assess patients, clinicians must maintain vital physical examination skills in addition to their knowledge and skills in the use of mechanical monitoring devices. Analysis of anesthetic mishaps leading to serious morbidity and mortality41 has consistently revealed one common mechanism as a root cause for catastrophe: failure to deliver oxygen to vital organs. The most common cause of critical end-organ hypoxia is failure to ventilate the lungs, hence the ASA recommendation for continuous evaluation of oxygenation and ventilation, even in healthy patients. The goal of this monitoring is early recognition of ventilatory inadequacy that can be rectified before end-organ damage ensues. Observation is still a vital skill in assessing tissue oxygenation, especially in the case of the awake patient. Signs of hypoxemia in an awake patient include decreased level of consciousness and loss of judgment and disorientation, but these signs are not specific and occur in many other conditions. Cyanosis may be an indicator of hypoxemia, but it occurs late and is generally unreliable. Given the devastating consequences of arterial hypoxemia, however, this cause must be at the top of any differential diagnosis when these physical signs are encountered.

Measurement of Oxygenation

Three methods of assessing oxygen delivery are widely available: arterial blood gas analysis, pulse oximetry, and measurement of inspired oxygen concentration. The need for blood gas analysis in healthy surgical patients is relatively rare. This test is invasive (and therefore has potential complications), relatively expensive, and can only be performed intermittently. Its use in healthy patients should be considered when complex surgical procedures are being performed or when perioperative complications necessitate in-depth analysis of ventilation and acid-base status. Pulse oximetry is completely noninvasive, well accepted (despite being a continuous monitor), and is relatively inexpensive. Extensive reviews of the development, theory, and applications of pulse oximetry are available. Pulse oximetry and inspired oxygen analysis should be used in every patient undergoing general anesthesia. Pulse oximetry should be used in all patients anesthetized with sedating IV medications. What follows is a summary of its technical aspects, perioperative uses, and limitations.

Pulse oximetry relies on two principles to continuously measure the degree of arterial blood oxygenation: differential light absorption of oxy- and deoxyhemoglobin, and pulsation of arterial blood. The pulse oximeter displays a number that corresponds to the arterial saturation obtained from an in vivo cooximeter. Also displayed on most units is a plethysmograph, or pulse waveform. Some advantages of pulse oximetry can also be viewed as limitations. First, the pulse oximeter is quite accurate when compared with in vivo oximetry but only under ideal conditions and within a fixed range of arterial saturation. Artifacts that create less than ideal conditions include shivering, cold extremity, intravascular dyes, venous congestion, and electrocautery. In addition, the processor algorithms built in to the device are unable to give meaningful output for oxygen saturations below 70%. Second, users must be familiar with limitations of the plethysmograph feature. It should not be assumed that the plethysmograph accurately reflects the magnitude of the arterial pulsation and hence the adequacy of perfusion. This signal is variably (and sometimes highly) amplified, however, to aid in the measurement of oxygen saturation.97 Hence the plethysmograph magnitude should not be used to infer information about the adequacy of blood perfusion.

Hemodynamic Monitors

Hemodynamic monitors are those intended to assess the adequacy of circulatory function. All anesthetized patients must have at least intermittent blood pressure monitoring. For healthy patients having uncomplicated surgical procedures, intermittent cuff measurement is usually sufficient. Cuff measurement of blood pressure can be achieved via either sphygmomanometry or oscillometry. Both methods are accurate, noninvasive, and well tolerated. Clinicians using either of these methods must understand a few guidelines to ensure accurate measurement. First, cuff size must be appropriate for the patient. Too large or too small cuff size can underestimate or overestimate blood pressure, respectively. This is most common in obese patients where cuff size is too small. Second, this method of blood pressure measurement is subject to motion artifact.

Direct intra-arterial blood pressure monitoring involves insertion of a catheter into an artery followed by connection to a pressure transduction system. Arterial cannulae are occasionally necessary in healthy patients, due to procedural length or complexity. This technique is invasive, and serious complications can result from its use. When correctly performed, this method provides continuous measurement of blood pressure that is very accurate. The data obtained from this measurement technique can even be used as an accurate measure of intravascular volume status.98

In patients who are intubated and mechanically ventilated, variation in the peak systolic pressure with ventilation has been used as a method to estimate intravascular volume status.99 This measurement, known as systolic pressure variation (SPV), has been compared with central venous pressure measurements, pulmonary artery occlusion pressure measurements, and transesophageal echocardiographic measurement of left ventricular volume, and it has been found to be more accurate than other pressure measurements for determining adequacy of volume resuscitation.99 Normal values of SPV are between 5 and 10 mm Hg, with greater values representing possible underresuscitation (hypovolemia) and lesser values implying that the patient may be overresuscitated.99 This SPV has been described as a "dynamic variable of volume responsiveness."99,100

Clinicians must not forget basic physical examination skills that can be valuable when specifically assessing circulatory status. The two most useful of these skills are palpation and auscultation. These tests can be immediately performed and require no mechanical devices. These methods are not sufficient to completely monitor the circulatory status in healthy patients. Regular use of these techniques, however (especially when baseline assessments were performed for comparison), can give anesthesia providers accurate and early information that may guide therapy or aid in selection of more complex assessment techniques. Palpation of a peripheral pulse can give valuable information about the circulatory status of the patient. Two properties of the pulse must be ascertained: magnitude and character. The pulse of a healthy patient at baseline should be strong and regular. Performing a baseline examination is mandatory so that later comparison can be made.

Auscultation is another physical examination skill with usefulness in the modern operating room. Auscultation is simple to perform, even on a continuous basis, and is an excellent qualitative measure of ventilation. Auscultation is most valuable to the clinician when a baseline examination is performed and used for later comparison. Baseline auscultation of heart and lungs should be performed in every anesthetized patient. As with palpation, both the quality and the magnitude of the sounds must be ascertained. Auscultation is never sufficient on its own to make definitive diagnoses or guide therapy, but it can be performed easily, immediately, and without harm and may guide the clinician in planning additional diagnostic steps. An example is development of a third heart sound, combined with new pulmonary rales, raising suspicion of fluid overload and pulmonary edema.

The heart is not only a pump, but a vital end organ, susceptible to hypoxic insult. In addition, even healthy anesthetized patients may be susceptible to cardiac rhythm abnormalities that can compromise circulatory adequacy. Therefore, anesthesiologists routinely monitor the integrity of the heart muscle and heart rhythm during anesthesia. This is accomplished mainly via ECG and, when possible, feedback from an awake patient (angina or anginal equivalent). ECG monitoring is considered the standard of care in modern anesthesia. ECG monitoring is completely noninvasive, relatively inexpensive, and can be assessed continuously. ECG is a crude representation of the heart's electrical activity, but critical information can be inferred from the trace regarding the integrity of the myocardium. Specific patterns of abnormality on ECG tracings can represent cardiac dysrhythmias, cardiac ischemia, and electrolyte imbalances that can compromise the integrity of the heart muscle and its function as a pump.

The most common ECG abnormality found in healthy anesthetized patients is dysrhythmia. Therefore, when using ECG to monitor in healthy patients, it is wise to monitor leads that are best suited for rhythm identification such as lead II or V1. Common causes of perioperative dysrhythmias are autonomic nervous system overactivity, ventilatory abnormalities such as hypoxemia and hypercarbia, and cardiac effects of anesthetic medications and adjuvants. Perioperative dysrhythmias in otherwise healthy patients are often well tolerated and self-limited. Some, such as severe bradycardia and junctional rhythms, can compromise circulatory status and require intervention. On occasion, the perioperative ECG will identify myocardial ischemia in patients who were previously thought to be healthy.

By definition, healthy patients are free of coronary artery disease. Use of perioperative ECG monitoring, however, will identify possible coronary ischemia in patients who were previously thought to be free of ischemic heart disease. The relationship between perioperative ECG evidence of coronary ischemia and the diagnosis of ischemic heart disease remains unclear. For ECG to function well as a monitor for myocardial ischemia, the correct combinations of leads must be used. Highest sensitivity can be achieved when these combinations include lead V5. Changes in ST segments and in T-wave configurations are the most universally accepted ECG findings representative of coronary ischemia, but specificity of these findings is far from perfect.101 Newer monitors use computer-assisted ST segment analysis to assist in early detection of coronary ischemia. Most monitors allow printing or "freezing" of a short ECG trace to compare with later findings. When these are not performed, clinicians should closely observe a preinduction ECG tracing so that comparisons can be made later, if necessary.

Capnography

Measurement of respiratory carbon dioxide is useful and strongly encouraged in all anesthetized patients. The methodology most commonly used is end-tidal carbon dioxide measurement, or capnography, to measure the carbon dioxide concentration in respiratory gas. Portable colorimetric devices are also available for use at the bedside or in the emergency department and are used to confirm proper placement of an endotracheal tube. Capnographic samples can be obtained from closed or open (eg, near the nose of a patient who is spontaneously breathing room air) breathing circuits. Capnography gives clinicians vital information regarding the pattern and the magnitude of ventilation. It gives useful information regarding cardiopulmonary function. To produce a normal capnogram, the patient must be producing carbon dioxide at the normal rate, blood must be returning it to the pulmonary circulation, and the lungs must be ventilated. Therefore, a continuous capnogram ensures, on a breath-to-breath basis, that all of the following are functioning normally: metabolism, blood flow, and ventilation.

A sudden decrease in end-tidal carbon dioxide may be an early and reliable indicator of pulmonary embolism.102 Capnography is useful in confirming proper placement of endotracheal tubes, but it is not useful in ruling out endobronchial intubation. End-tidal carbon dioxide concentration can be monitored continuously, the machinery is relatively inexpensive, and the technique is noninvasive.

Mental Status and Depth of Anesthesia

The best monitor of cerebral function in healthy patients requiring anesthesia is interaction with a conscious patient. This is the rationale for using awake anesthetic techniques in certain settings where feedback regarding brain integrity is critical (carotid endarterectomy, prostatic resection with use of nonionic irrigants). In many surgical settings, however, awake anesthetic techniques are not suitable. A concept intimately related to perioperative cerebral function is the ability of anesthesia providers to assess the efficacy, or "depth" of anesthesia accurately in unconscious patients. The ideal general anesthetic renders a patient unconscious and pain free, facilitates ideal surgical working conditions, is rapidly reversible at the conclusion of surgery, and has no lasting side effects. During anesthesia-induced unconsciousness, however, there is no completely reliable method of assessing whether a patient is aware and possibly perceiving intraoperative events. Anesthesia providers undergo rigorous training in pharmacology and physiology to dose medications and interpret physiologic data correctly so that they can provide assurance on these grounds that patients are adequately anesthetized. Unfortunately, correct drug dosing and "normal" physiologic values do not ensure that all patients are unconscious and free from pain.

EEG is used only occasionally for monitoring brain function (and presumably, consciousness). This monitoring technique is cumbersome, expensive, and requires highly trained personnel to interpret the complex data that it generates. Currently, unprocessed EEG is rare in intraoperative settings. A variation of EEG that has gained attention in both the medical community and with the lay media is BIS or "entropy" monitoring. These devices use only select EEG leads and then filter and transform the signals into a single digitized value.103 BIS or entropy values correlate inversely with depth of anesthesia.103 Use of the device has been advocated for two reasons: reducing the incidence of intraoperative awareness during general anesthesia and reducing anesthetic drug costs.104 Although intraoperative awareness is a real problem, the issue has been somewhat sensationalized by the public media, which has led to much public interest in BIS. The ability of BIS to eliminate awareness, however, remains controversial,105 and some even argue that BIS could actually cause anesthesiologists to underdose their medications, leading to a higher incidence of awareness.106 This issue remains unsettled and requires further investigation.

Temperature Monitoring

Temperature must be monitored in some way in all anesthetized patients, especially when general anesthesia is chosen or when MH-triggering agents are used. Multiple investigators have shown improved outcome with maintenance of normothermia during major operations.107 Hypothermia slows metabolism, inhibits coagulation, can cause cardiovascular lability, and is very uncomfortable in awake patients. Hypothermia is easily and commonly achieved in the operating room, but the best treatment strategy is prevention. Several methods of temperature monitoring are available to anesthesia providers. The simplest and least invasive method is use of a skin temperature probe. These probes are somewhat accurate, but it must be kept in mind that skin temperature is not truly representative of core, or internal, temperature. In addition, skin probes are easily rendered inaccurate by ambient conditions such as warming and cooling mattresses and forced air blowers. Several semi-invasive methods of temperature monitoring are available such as tympanic, nasopharyngeal, esophageal, and rectal. Although these methods are quite safe, accurate, and more reflective of core temperature, complications are possible (ruptured tympanic membrane, nosebleed, irretrievable probe wires). The most accurate monitors of core body temperature are also the most invasive. Temperature probes are present on the tips of pulmonary artery and urinary catheters, but these are generally reserved for major operations in medically ill patients.

Safety and efficacy are the primary determinants of a successful anesthetic. Safety in anesthesia is mainly achieved through the avoidance of complications. A main source of complications is patient comorbidity. Healthy patients, by definition, lack comorbidity but may still experience anesthetic complications. The main goals of the anesthetic plan in healthy patients are ensuring the absence of comorbidity and the identification of potential complicating factors. The primary method of accomplishing these goals is the careful performance of a preoperative history and physical examination, which is typically a joint effort between the surgeon and anesthesiologist. In most cases, the anesthetic portion of this evaluation can be performed on the same day as surgery. Once the evaluation of the healthy surgical patient is complete, the plan is formulated, taking into account the needs of both the patient and the surgeon. The patient must be fully informed of the nature of the operation and type of anesthesia involved. Patient instructions and use of premedications are also important steps leading to safe and successful anesthesia. Finally, monitoring devices are believed to be a major contributor to avoidance of complications and overall patient safety. Generally, healthy patients only need basic ASA intraoperative monitoring, but, on occasion, the extent of surgery may dictate a more invasive monitoring scheme.

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