Anesthetic risk is difficult to ascertain precisely in most cases. Perioperative complications and deaths are frequently caused by a combination of factors, including concurrent disease, complexity of the operation, and adverse effects of anesthesia. A few complications are due entirely to anesthesia, such as aspiration pneumonitis and hypoxemia due to failure to maintain a patent airway. While many classifications exist, the patient’s physical status according to the criteria is the most widely known. This classification system was not specifically designed to estimate anesthetic risk but does provide a “common language” of evaluation for use by different institutions.
Method and Site of Preoperative Evaluations
Historically, patients were evaluated the night before surgery in the hospital. That approach has mostly been abandoned because most patients (even for complicated surgery) enter the hospital the morning of surgery. Although low-risk patients are interviewed by telephone, higher-risk patients should be evaluated in a preoperative evaluation clinic (or its equivalent) one or more days preoperatively. Preoperative clinics not only prepare patients for anesthesia and surgery but also enhance the efficiency and economics of the perioperative experience (eg, decreased surgical cancellations). They also follow protocols, which can ensure that only proper and necessary laboratory and radiologic tests are performed. However, the logistics dictate that the person performing the preoperative evaluation will not be the anesthesiologist who will be delivering the anesthetic. Nevertheless, all the preoperative information will be ready for the anesthesia team actually giving the anesthetic. The team will actually meet the patient in person for the first time 1 hour or less before surgery. This places tremendous emphasis on the adequacy of the telephone and clinic visits to make certain that patients are adequately prepared for anesthesia and surgery.
History and Physical Examination
The history should include a review of previous experiences with anesthesia, and data should be elicited regarding any allergic reactions, delayed awakening, prolonged paralysis from neuromuscular blocking drugs, and jaundice. Knowledge of exercise tolerance, history of the present illness, and the last visit with the patient’s primary care doctor is helpful. The presence and severity of any concurrent diseases (eg, hepatitis), coagulopathies, endocrine abnormalities (eg, diabetes mellitus), or cardiorespiratory dysfunction should be noted. The patient’s social history (ie, drug, alcohol, and tobacco use, and family history) should be sought.
The physical examination should focus on the cardiovascular system, lungs, and upper airway. It should include measurements of heart rate and of arterial blood pressure obtained in both the supine and standing positions and auscultation for cardiac murmurs, carotid artery bruits, or abnormal breathing. If abnormalities are found, additional tests (electrocardiography, pulmonary function tests) may be indicated. The airway, head, and neck should be examined for factors that could make endotracheal intubation difficult, eg, fat or short neck, limited temporomandibular mobility. Since over 50% of all anesthetic-induced morbidity and mortality is related to inability to maintain the airway, examination of the airway demands special emphasis. The most common scoring of the airway as an assessment of a possible difficult endotracheal intubation is the “Mallampati classification.” When the patient’s uvula is visible with the mouth open, the score is grade I (easy intubation); in contrast, grade IV exists when the hard palate is visible but not the soft palate. Grade IV suggests a technically difficult endotracheal intubation.
Peripheral venous sites, including the external jugular vein, should also be checked. If regional anesthesia is planned, the proposed site of injection should be examined for abnormalities, signs of infection, and a limited neurologic examination should be performed.
Evaluation of Concurrent Drug Therapy
Concurrent drug therapy must be reviewed. Although many drugs can interact with anesthetic drugs, the influence of concurrent drug therapy on overall or perioperative care is substantial. Smoking and alcohol are well-known factors influencing anesthetic requirement and the postoperative outcome. Tricyclic antidepressants exaggerate the sympathomimetic response of many vasopressors, but antihypertensive and antiarrhythmic drugs can decrease peripheral sympathetic activity and augment the depressant effect of anesthetics. Patients whose hypertension is being treated with angiotensin receptor antagonists seem to have more trouble with hypotension intraoperatively. Certainly, drug therapy associated with concurrent diseases must be individually considered and continued as guided by specific disease-designated protocols (eg, hypertension, diabetes, ischemic heart disease). Lastly, patients are increasingly taking complementing and alternative medications about which little is known but that have the potential for serious interactions with other drugs and anesthesia. Herbal medicines and dietary supplements are of special concern. Increasing amounts of information are becoming available. Obviously, the safety of continuing drug therapy depends on awareness of potential drug interactions.
Mechanisms by Which Drugs May Influence Effects of Anesthesia.
Anesthetic requirements may be increased or decreased.
Neuromuscular blockade from muscle relaxants may be enhanced.
Cardiovascular response to sympathomimetics and anesthetics may be exaggerated.
Peripheral sympathetic nervous system activity may be reduced, and cardiovascular depressant reactions to anesthetics may be augmented.
Metabolism may be enhanced or impaired.
Certain drugs probably should be started preoperatively, especially for moderately or extensively invasive procedures. These include beta-adrenergic receptor blockade and statins for 2 weeks preoperatively. Small-dose aspirin, unless surgically contraindicated, a physical activity regimen, and smoking cessation are all helpful.
Preoperative Laboratory Tests
In the past, hospital rules mandated that a large battery of screening laboratory tests be given prior to anesthesia; however, many of these tests have been found to be unnecessary, and the advisability of others has been questioned. For example, one common rule is that elective surgery should not be performed if the hemoglobin concentration is less than 10 g/dL. There is no evidence, however, that correction of normovolemic anemia decreases perioperative morbidity and mortality rates. More important is the need to determine why the patient is anemic.
The history, physical examination are the most valuable guides for determining which laboratory tests are necessary (eg, a long history of smoking dictates a thorough examination of pulmonary status by means of pulmonary function tests). Men aged 40 years or younger with no history of problems with anesthesia and normal findings on physical examination usually require no laboratory tests; women of this age and health status usually require only hemoglobin measurements. Recently, the American Society of Anesthesiologists produced a preoperative testing advisory in which it divided surgical procedures into three classes: minimally or moderately invasive procedures and those that disrupt normal physiology.
For the last, most invasive category, a complete blood count, platelet count, measurement of electrolytes and creatinine are usually recommended. An electrocardiogram is indicated for the last two categories. Other tests are based on comorbid conditions. A creatinine level measurement is usually indicated when the patient is to receive contrast dye.
Questionnaires, some via computers, are a useful means of identifying patients likely to have complications who would therefore benefit from preoperative laboratory testing. This is especially important with increasing emphasis on same-day surgery. Because increasing numbers of medical centers have integrated computerized systems, the results from preoperative and preprocedure assessment clinics will be a prominent part of these systems. Excessive testing can even be hazardous, because borderline abnormalities may lead to additional—sometimes invasive—tests or therapy. An example is potassium treatment for borderline low potassium levels.
Anesthesia Preoperative Evaluation: Summary
The three major goals of preoperative evaluation can be briefly stated as follows:
to make certain that the patient is in optimal condition for anesthesia (eg, antibiotic therapy for respiratory infection in a patient with emphysema);
to understand the patient’s concurrent diseases and drug therapy;
to ensure that all of the patient’s questions and concerns are adequately addressed.