The cornerstones of an effective preoperative evaluation are the medical history and physical examination, which should include a complete account of all medications taken by the patient in the recent past, all pertinent drug and contact allergies, and responses and reactions to previous anesthetics. Additionally, this evaluation should include any indicated diagnostic tests, imaging procedures, or consultations from other physicians. The preoperative evaluation guides the anesthetic plan: inadequate preoperative planning and incomplete patient preparation are commonly associated with anesthetic complications.
The preoperative evaluation serves multiple purposes. One purpose is to identify those few patients whose outcomes likely will be improved by implementation of a specific medical treatment (which in rare circumstances may require that the planned surgery be rescheduled). For example, a 60-year-old patient scheduled for elective total hip arthroplasty who also has unstable angina from left main coronary artery disease would more likely survive if coronary artery bypass grafting is performed before the elective procedure. Another purpose is to identify patients whose condition is so poor that the proposed surgery might only hasten death without improving the quality of life. For example, a patient with severe chronic lung disease, end-stage kidney failure, liver failure, and heart failure likely would not survive to derive benefit from an 8-hour, complex, multilevel spinal fusion with instrumentation.
The preoperative evaluation can identify patients with specific characteristics that likely will influence the proposed anesthetic plan (Table 18-1). For example, the anesthetic plan may need to be reassessed for a patient whose trachea appears difficult to intubate, one with a family history of malignant hyperthermia, or one with an infection near where a proposed regional anesthetic would be administered. Another purpose of the evaluation is to provide the patient with an estimate of anesthetic risk.
However, the anesthesiologist should not be expected to provide the risk-versus-benefit discussion for the proposed procedure; this is the responsibility and purview of the responsible surgeon or “proceduralist.” For example, a discussion of the risks and benefits of robotic prostatectomy versus radiation therapy versus “watchful waiting” requires knowledge of both the medical literature and the morbidity-mortality statistics of an individual surgeon, and it would be most unusual for an anesthesiologist to have access to the necessary data for this discussion. Finally, the preoperative evaluation is an opportunity for the anesthesiologist to describe the proposed anesthetic plan in the context of the overall surgical and postoperative plan, provide the patient with psychological support, and obtain informed consent for the proposed anesthetic plan from the surgical patient.
By convention, physicians in many countries use the American Society of Anesthesiologists’ (ASA) classification to define relative risk prior to conscious sedation and surgical anesthesia (Table 18-2). The ASA physical status classification has many advantages over all other risk classification tools: it is time honored, simple, reproducible, and, most importantly, it has been shown to be strongly associated with perioperative risk. But, many other risk assessment tools are available.
Elements of the Preoperative History
Patients presenting for elective surgery and anesthesia typically require a focused preoperative medical history emphasizing cardiac and pulmonary function, kidney disease, endocrine and metabolic diseases, musculoskeletal and anatomic issues relevant to airway management and regional anesthesia, and responses and reactions to previous anesthetics. The ASA publishes and periodically updates general guidelines for preoperative assessment (see Guidelines).
Guidelines for preoperative cardiac assessment are available from the American College of Cardiology/American Heart Association and from the European Society of Cardiology (see Guidelines). A more complete discussion of cardiovascular assessment is provided in Chapter 21. The focus of preoperative cardiac assessment should be on determining whether the patient’s condition can and must be improved prior to the scheduled procedure, and whether the patient meets criteria for further cardiac evaluation prior to the scheduled surgery. Clearly the criteria for what must be done before elective arthroplasty will differ from what must be done before an operation for resectable pancreatic cancer, given the benign results of a delay in the former procedure and the potential life-shortening effects of a delay in the latter procedure.
In general, the indications for cardiovascular investigations are the same in surgical patients as in any other patient. Put another way, the fact that a patient is scheduled to undergo surgery does not change the indications for such measures as noninvasive stress testing to diagnose coronary artery disease.
Perioperative pulmonary complications, most notably postoperative respiratory depression and respiratory failure, are vexing problems that have become seemingly more common as severe obesity and obstructive sleep apnea have increased in incidence. A recent guideline developed by the American College of Physicians takes an aggressive stance; it identifies patients 60 years of age or older, those with chronic obstructive lung disease, those with markedly reduced exercise tolerance and functional dependence, and those with heart failure as potentially requiring preoperative and postoperative interventions to avoid complications. The risk of postoperative pulmonary complications is closely associated with these factors, and with the following: ASA class (class 3 and 4 patients have a markedly increased risk of pulmonary complications relative to class 1 patients), cigarette smoking, longer surgeries (>4 h), certain types of surgery (abdominal, thoracic, aortic aneurysm, head and neck, and emergency surgery), and general anesthesia (compared with cases in which general anesthesia was not used).
Efforts at prevention of pulmonary complications should focus on cessation of cigarette smoking prior to surgery and on lung expansion techniques (eg, incentive spirometry) after surgery in patients at risk. Patients with asthma, particularly those receiving suboptimal medical management, have a greater risk for bronchospasm during airway manipulation. Appropriate use of analgesia and monitoring are key strategies for avoiding postoperative respiratory depression in patients with obstructive sleep apnea. Further discussion of this topic appears in Chapter 44.
Endocrine and Metabolic Issues
Appropriate targets for control of diabetes mellitus and of blood glucose in critically ill patients have been subjects of great debate over the past decade. “Tight” control of blood glucose, with a target level in the normal range, was shown in the Diabetes Control and Complications Trial to improve outcomes in ambulatory patients with type 1 diabetes mellitus. It has become the usual practice to obtain a blood glucose measurement on the morning of elective surgery. Unfortunately, many diabetic patients presenting for elective surgery do not maintain blood glucose within the desired range. Other patients, who may be unaware that they have type 2 diabetes, present with blood glucose measurements above the normal range.
Adequacy of long-term blood glucose control can be easily and rapidly assessed by measurement of hemoglobin A1c
. In patients with abnormally elevated hemoglobin A1c
, referral to a diabetology service for education about the disease and adjustment of diet and medications to improve metabolic control may be beneficial. Elective surgery should be delayed in patients presenting with marked hyperglycemia; this delay might consist only of rearranging the order of scheduled cases to allow insulin
infusion to bring the blood glucose concentration closer to the normal range before surgery begins. A more complete discussion of diabetes mellitus and other perioperative endocrine concerns is provided in Chapter 34.
Three important coagulation issues that must be addressed during the preoperative evaluation are (1) how to manage patients who are taking warfarin on a long-term basis; (2) how to manage patients who are taking clopidogrel and related agents; and (3) how to safely provide regional anesthesia to patients who either are receiving long-term anticoagulation therapy or who will receive anticoagulation perioperatively. In the first circumstance, most patients who undergoing anything more involved than minor surgery will require discontinuation of warfarin 5 days in advance of surgery to avoid excessive blood loss. The key question to be answered is whether the patient will require “bridging” therapy with another agent while warfarin is discontinued.
In patients deemed at high risk for thrombosis (eg, those with certain mechanical heart valve implants or with atrial fibrillation and a prior thromboembolic stroke), warfarin
should be replaced by intravenous heparin
or, more commonly, by intramuscular heparinoids to minimize the risk. In patients receiving bridging therapy for a high risk of thrombosis, the risk of death from excessive bleeding is an order of magnitude lower than the risk of death or disability from stroke if the bridging therapy is omitted. Patients at lower risk for thrombosis may have warfarin
discontinued and then reinitiated after successful surgery. Decisions regarding bridging therapy often require consultation with the physician who initiated the warfarin
Clopidogrel and related agents are most often administered with aspirin (so-called dual antiplatelet therapy) to patients with coronary artery disease who have received intracoronary stenting. Immediately after stenting, such patients are at increased risk of acute myocardial infarction if clopidogrel (or related agents) and aspirin are abruptly discontinued for a surgical procedure.
Therefore, current guidelines recommend postponing all but mandatory emergency surgery until at least 1 month after any coronary intervention and suggest that treatment options other
than a drug-eluting stent (which will require prolonged dual antiplatelet therapy) be used in patients expected to undergo a surgical procedure within 12 months after the intervention (eg, in a patient with colon cancer who requires treatment for coronary disease). As the available drugs, treatment options, and consensus guidelines are updated relatively frequently, we recommend consultation with a cardiologist regarding safe management of patients receiving these agents who require a surgical procedure.
The third circumstance—when it may be safe to perform regional (particularly neuraxial) anesthesia in patients who are or will be receiving anticoagulation therapy—has also been the subject of debate among hematologists and regional anesthetists. The American Society of Regional Anesthesia publishes a periodically updated consensus guideline on this topic, and other prominent societies (eg, the European Society of Anaesthesiologists) also provide guidance on this topic. This topic is considered in greater detail in Chapter 45.
Since Mendelson’s 1946 report, aspiration of gastric contents has been recognized as a potentially disastrous pulmonary complication of surgical anesthesia. It has also been long recognized that the risk of aspiration is increased in certain groups of patients: pregnant women in the second and third trimesters, those whose stomachs have not emptied after a recent meal, and those with serious gastroesophageal reflux disease (GERD).
Although there is a consensus that pregnant women and those who have recently (within 6 h) consumed a full meal should be treated as if they have “full” stomachs, there is less consensus as to the necessary period of time in which patients must fast before elective surgery. Proof of the lack of consensus is the fact that the ASA’s guideline on this topic was voted down by the ASA House of Delegates several years in a row before it was presented in a form that received majority approval. The guideline as approved is more permissive of fluid intake than many anesthesiologists would prefer, and many medical centers have policies that are more restrictive than the ASA guideline on this topic.
The truth is that there are no good outcomes data to support restricting fluid intake (of any kind or any amount) more than 2 h before induction of general anesthesia in healthy patients undergoing elective procedures; indeed, there is evidence that nondiabetic patients should be encouraged to drink glucose-containing fluids up to 2 h before induction of anesthesia.
Patients with a history of GERD present vexing problems. Some of these patients will clearly be at increased risk for aspiration; others may carry this “self-diagnosis” based on television advertisements or conversations with friends and family, or may have been given this diagnosis by a physician who did not follow the standard diagnostic criteria. Our approach is to treat patients who have only occasional symptoms like any other patient without GERD, and to treat patients with consistent symptoms (multiple times per week) with medications (eg, nonparticulate antacids such as sodium citrate) and techniques (eg, tracheal intubation rather than laryngeal mask airway) as if they were at increased risk for aspiration.
Elements of the Preoperative Physical Examination
The preoperative history and physical examination complement one another: The physical examination may detect abnormalities not apparent from the history, and the history helps focus the physical examination. Examination of healthy asymptomatic patients should include measurement of vital signs (blood pressure, heart rate, respiratory rate, and temperature) and examination of the airway, heart, lungs, and musculoskeletal system using standard techniques of inspection, auscultation, palpation, and percussion. Before procedures such as a nerve block, regional anesthesia, or invasive monitoring the relevant anatomy should be examined; evidence of infection near the site or of anatomic abnormalities may contraindicate the planned procedure (see Chapters 5, 45, and 46). An abbreviated neurological examination is important when regional anesthesia will likely be used. The preoperative neurological examination serves to document whether any neurological deficits may be present before the block is performed.
The anesthesiologist must examine the patient’s airway before every anesthetic procedure. The patient’s dentition should be inspected for loose or chipped teeth, caps, bridges, or dentures. Poor fit of the anesthesia mask should be expected in edentulous patients and those with significant facial abnormalities. Micrognathia (a short distance between the chin and the hyoid bone), prominent upper incisors, a large tongue, limited range of motion of the temporomandibular joint or cervical spine, or a short or thick neck suggest that difficulty may be encountered in direct laryngoscopy for tracheal intubation (see Chapter 19).
Preoperative Laboratory Testing
Routine laboratory testing when patients are fit and asymptomatic is not recommended. Testing should be guided by the history and physical examination. “Routine” testing is expensive and rarely alters perioperative management; moreover, abnormal values often are overlooked or if recognized may result in unnecessary delays. Nonetheless, despite the lack of evidence of benefit, many physicians order a hematocrit or hemoglobin concentration, urinalysis, serum electrolyte measurements, coagulation studies, an electrocardiogram, and a chest radiograph for all patients, perhaps in the misplaced hope of reducing their exposure to litigation.
To be valuable, preoperative testing must discriminate: there must be an increased perioperative risk when the results are abnormal (and unknown when the test is not performed), and there must be a reduced risk when the abnormality is not detected (or it has been corrected). This requires that the test have a very low rate of false-positive and false-negative results. The utility of a test depends on its sensitivity and specificity. Sensitive tests have a low rate of false-negative results and rarely fail to identify an abnormality when one is present, whereas specific tests have a low rate of false-positive results and rarely identify an abnormality when one is not present
. The prevalence of a disease or of an abnormal test result varies with the population tested. Testing is therefore most effective when sensitive and specific tests are used in patients in whom the abnormality will be detected frequently enough to justify the expense and inconvenience of the test procedure. Accordingly, laboratory testing should be based on the presence or absence of underlying diseases and drug therapy as detected by the history and physical examination. The nature of the proposed surgery or procedure should also be taken into consideration. Thus, a baseline hemoglobin or hematocrit measurement is desirable in any patient about to undergo a procedure that may result in extensive blood loss and require transfusion, particularly when there is sufficient time to correct anemia preoperatively (eg, with iron supplements).
Testing fertile women for an undiagnosed early pregnancy is controversial and should not be done without the permission of the patient; pregnancy testing involves detection of chorionic gonadotropin in urine or serum. Routine testing for HIV antibody is not indicated. Routine coagulation studies and urinalysis are not cost-effective in asymptomatic healthy patients; nevertheless, a preoperative urinalysis is required by state law in at least one U.S. jurisdiction.