American Society of Anesthesiologists Classification and Risk Stratification

Approximately 27 million patients undergo surgery each year in the United States and 8 million or 30% have significant coronary artery disease or other cardiac comorbidities. Appropriately, the cardiovascular system is targeted during the preoperative assessment of patients. The ASA classification was first developed in 1961 and has been revised to categorize risk into six stratifications.

The goal of the classification system is to assess the overall physical status of the patient before surgery (not to assess surgical risk), and although quite subjective, it remains as a significant independent predictor of mortality (Davenport et al, 2006). Other tools to assess the preoperative risks were developed by multivariate statistical analysis of patient-related factors correlated with surgical outcomes. One such scoring system, Goldman’s criteria (Table 6–1), assigns points to easily reproducible characteristics. The points are then added to compute the perioperative risk of cardiac-related complication. Another system, the Cardiac Risk Index, simplified this concept employing only six predictors to estimate cardiac complication risk in noncardiac surgical patients (Table 6–2) (Akhtar and Silverman, 2004).

Table 6–1 Goldman’s Cardiac Risk Index

Table 6–2 Modified Cardiac Risk Index

Cardiac Evaluation

The preoperative cardiac evaluation, which consists of an initial history and physical examination and ECG, attempts to identify potential serious cardiac disorders such as coronary artery disease, heart failure, symptomatic arrhythmias, the presence of a pacemaker or implantable defibrillator, or a history of orthostatic hypotension (Eagle et al, 1996). Furthermore, it is essential to define the severity and stability of existing cardiac disease before surgery. Cardiac-specific risk is also altered by the patient’s functional capacity, age, and other comorbid conditions such as diabetes, peripheral vascular disease, renal dysfunction, and chronic obstructive pulmonary disease. The American College of Cardiology and American Heart Association recently collaborated to develop guidelines regarding perioperative cardiac evaluation before surgery (Fleisher et al, 2007a). The guidelines generally use three categories of clinical risk predictors: clinical markers, functional capacity, and type of surgical procedure (Eagle et al, 2002).

Clinical Markers

The major clinical predictors of increased perioperative cardiovascular risk are a documented acute myocardial infarction less than 7 days previously, a recent myocardial infarction (defined as >7 days but <1 month before surgery), unstable angina, evidence of any ischemic burden by clinical symptoms or noninvasive testing, decompensated heart failure, significant arrhythmias, and severe valvular disease. Intermediate predictors include mild angina, previous myocardial infarction by history or pathologic Q waves, compensated heart failure, diabetes, or renal insufficiency (creatinine >2 mg/dL). Minor predictors of risk are advanced age, abnormal electrocardiogram, rhythms other than sinus (i.e., atrial fibrillation), history of stroke, or uncontrolled systemic hypertension. The historical dictum of the timing of elective surgery after a myocardial infarction into a 3-month and 6-month interval is now currently avoided (Tarhan et al, 1972). The ACC cardiovascular database committee stratifies risk on the basis of the severity of the myocardial infarction and the likelihood of reinfarction based on a recent exercise stress test. However, in the absence of adequate clinical trials on which to base firm recommendations, it is reasonable to wait 4 to 6 weeks after myocardial infarction to perform elective surgery.

Functional Capacity

Functional capacity, or one’s ability to meet aerobic demands for a specific activity, is quantified as metabolic equivalents or METs. For example, a 4-MET demand is comparable with a patient’s ability to climb two flights of stairs. This simple measurement continues to be an easy and inexpensive method to determine a patient’s cardiopulmonary functional capacity (Biccard, 2005). The Duke Activity Status Index (Table 6–3) allows the physician to easily determine a patient’s functional capacity (Hlatky et al, 1989). Generally, a capacity of 4 METs indicates no further need for invasive cardiac evaluation.

Table 6–3 Duke Activity Status Index*

Duke activity status index (DASI) = SUM (values for all 12 questions).

Estimated Peak Oxygen Uptake (VO_2peak) in mL/min = (0.43 × [DASI]) + 9.6.

VO_2peak mL/kg/min × 0.286 (mL/kg/min)⁻¹ = METS.

* The most widely recognized measure of cardiorespiratory fitness is maximal oxygen consumption (VO_2peak) measured in mL/kg/min. The Index score correlates directly with VO_2peak and therefore is an indirect measure of maximal METS.

Surgery-Specific Cardiac Risk

Two important factors determine the surgery-specific cardiac risk: the type of surgery and the degree of hemodynamic stress. Surgery-specific risk is stratified into high-, intermediate-, and low-risk procedures. High-risk procedures include both major emergent surgery, particularly in the elderly, and surgery associated with increased operative time resulting in large fluid shifts or blood loss. Intermediate risk procedures include intraperitoneal surgery, laparoscopic procedures, and robotic-assisted laparoscopic surgeries. Low-risk procedures include endoscopic procedures or superficial surgeries (i.e., not involving entrance into a body cavity) (Eagle et al, 2002).

Pulmonary

Preoperative pulmonary evaluation is important in all urologic procedures but critical in those surgeries involving the thoracic or abdominal cavities. These later procedures, which include intra-abdominal, laparoscopic, or robotic surgeries, can decrease pulmonary function and predispose to pulmonary complications. Accordingly, it is wise to consider pulmonary functional assessment in patients who have significant underlying medical disease, significant smoking history, or overt pulmonary symptoms. Pulmonary function tests that include a forced expiratory volume in 1 second (FEV₁), forced vital capacity, and the diffusing capacity of carbon monoxide are quite easily obtainable and provide a preoperative baseline. Patients with an FEV₁ of less than 0.8 L/sec or 30% of predicted are at high risk for complications (Arozullah et al, 2003). Specific pulmonary risk factors include chronic obstructive pulmonary disease, smoking, preoperative sputum production, pneumonia, dyspnea, and obstructive sleep apnea. It has been shown that smokers have a fourfold increased risk for postoperative pulmonary morbidity and as high as a 10-fold higher mortality rate (Fowkes et al, 1982). In general, it is interesting to note that patients with restrictive pulmonary disease fare better than those with obstructive pulmonary disease because the former group maintains an adequate maximal expiratory flow rate, which allows for a more effective cough with less sputum production (Pearce and Jones, 1984). In addition to the specific pulmonary risk factors, general factors contribute to increased pulmonary complications such as increased age, lower serum albumin levels, obesity, impaired sensorium, previous stroke, immobility, acute renal failure, and chronic steroid use.

Specific preoperative interventions can decrease pulmonary complications. Smoking must be discontinued at least 8 weeks before surgery to achieve a risk reduction. Patients who discontinue smoking less than 8 weeks before surgery may actually have a higher risk of complication because the acute absence of the noxious effect of cigarette smoke decreases postoperative coughing and pulmonary toilet. However, patients who have stopped smoking at least 8 weeks preoperatively will significantly lower their complication rate, and patients who have ceased smoking for more than 6 months have a pulmonary morbidity comparable with nonsmokers (Warner et al, 1989). The use of preoperative bronchodilators in COPD patients can dramatically reduce postoperative pulmonary complications. Aggressive treatment of preexisting pulmonary infections with antibiotics, as well as the pretreatment of asthmatic patients with steroids, is essential in optimizing pulmonary performance. Likewise, the use of epidural and regional anesthetics, vigorous pulmonary toilet, rehabilitation, and continued bronchodilation therapy are all beneficial (Arozullah et al, 2003).

Hepatobiliary

Because the survival of patients with advanced liver disease has improved over the past decade, surgery is being performed more frequently in these patients. Furthermore, patients with mild to moderate hepatic disease are often asymptomatic. These patients need to be identified and evaluated before surgery. Patients are usually aware of a prior diagnosis of hepatitis, and they should be questioned regarding the timing of diagnosis and the precipitating factors. This history is particularly important in a situation when a member of the health care team is inadvertently stuck with a needle or scalpel during the surgical procedure. A review of systems should include questions regarding pruritus, excessive bleeding, abnormal abdominal distention, and weight gain. On physical examination, jaundice and scleral icterus may be evident with serum bilirubin levels higher than 3 mg/dL. Skin changes such as caput medusae, palmar erythema, spider angiomas, and clubbing all indicate hepatic dysfunction. Severe manifestations include abdominal distention, encephalopathy, asterixis, or cachexia. Again, identification of underlying hepatic illness is important in the preoperative risk assessment of the patient. Although the estimation of perioperative mortality is limited by the lack of high-quality clinical studies, the use of the Child classification and Model for End-Stage Liver Disease (MELD) score offers a reasonable estimation.

The Child classification assesses perioperative morbidity and mortality in patients with cirrhosis and is based on the patient’s serum markers (bilirubin, albumin, prothrombin time) and severity of clinical manifestations (i.e., encephalopathy and ascites). Mortality risk for patients undergoing surgery stratified by Child class is as follows: Child Class A—10%, Child Class B—30%, and Child Class C—76% to 82%. The Child classification also correlates with the frequency of complications such as liver failure, encephalopathy, bleeding, infection, renal failure, hypoxia, and intractable ascites. Independent risk factors other than the Child class that can increase the mortality rate in patients with liver disease include emergency surgery and chronic obstructive pulmonary disease (O’Leary et al, 2009; Pearce and Jones, 1984).

The MELD score is perhaps a more accurate assessment of perioperative mortality in patients with hepatic dysfunction. The score is derived from a linear regression model based on serum bilirubin, creatinine levels, and the international normalized ratio (INR). It is more accurate than the Child classification in that it is objective, gives weights to each variable, and does not rely on arbitrary cut-off values (Teh et al, 2007). Clinicians can use a website (http://mayoclinic.org/meld/mayomodel9.html) to calculate the 7-day, 30-day, 90-day, 1-year, and 5-year surgical mortality risk on the basis of the patient’s age, ASA class, INR, serum bilirubin, and creatinine levels. Taken together, the Child classification and the MELD score complement each other and provide an accurate assessment of the risk of surgery in cirrhotic patients (O’Leary and Friedman, 2007; O’Leary et al, 2009).

Elderly

In the next 20 years, the percentage of patients older than 85 years of age may reach 5% or 15 million people. This represents a rapidly growing segment of our aging population (Monson et al, 2003). Accordingly, octogenarians and nonagenarians are undergoing an increasing number of surgeries annually. Because of the elderly patients’ special physiologic, pharmacologic, and psychologic needs, a unique set of health care challenges are encountered. It is still unclear whether advanced age independently predicts surgical risk or whether it is coexisting medical conditions that adversely affect surgical outcomes. However, in a large study published by Turrentine, it was shown that increased age independently predicted morbidity and mortality (Turrentine et al, 2006). This confirmed the study by Vemuri, who also found increased age as an independent risk factor for morbidity and mortality in patients undergoing aneurysm surgery (Vemuri et al, 2004). The studies suggest that perhaps the elderly patient cannot meet the increased functional demand required during perioperative and postoperative period. Hypertension and dyspnea were the most frequently seen comorbid risk factors in patients older than 80 years, and preoperative transfusion history, emergency operation, and weight loss best predicted postoperative morbidity. Each 30-minute increment of operative time increased the odds of mortality by 17% in octogenarians (Turrentine et al, 2006). A unique and important factor in the perioperative care of the elderly is in the identification and prevention of delirium. Often overlooked as “sundowning,” delirium can be the first clinical sign of metabolic and infectious complications (Townsend et al, 2008).

Morbid Obesity

With the rising incidence of obesity, as well as the vast experience gathered from bariatric surgery, the care of the morbidly obese patient has been extensively studied. One must carefully weigh the risk of any surgical procedure with the natural history of the disease when deciding the optimal time of the surgery in the morbidly obese. It is estimated that patients with a body mass index (BMI) of greater than or equal to 45 kg/m² may lose anywhere from 8 to 13 years of life (Fontaine et al, 2003). The careful selection of the morbidly obese patient for elective surgery is of paramount importance. Cardiac symptoms such as exertional dyspnea and lower extremity edema are nonspecific in the morbidly obese patients, and many of these patients have poor functional capacity. The physical examination often underestimates cardiac dysfunction in the severely obese patient. Severely obese patients with greater than three coronary heart disease risk factors may require noninvasive cardiac evaluation (Poirier et al, 2009). Obesity is associated with a vast array of comorbidities. Morbidly obese patients often have atherosclerotic cardiovascular disease, heart failure, systemic hypertension, pulmonary hypertension related to sleep apnea and obesity, hypoventilation, cardiac arrhythmias, deep vein thrombosis, history of pulmonary embolism, and poor exercise capacity. There are also numerous pulmonary abnormalities that result in a ventilation perfusion mismatch and alveolar hypoventilation. Obesity is a risk factor for postoperative wound infections, and, when appropriate, laparoscopic surgery should be considered.

Pregnancy

Urologic surgery in the pregnant woman is generally related to the management of renal colic and urinary tract stones. In the asymptomatic woman, the stones can be discovered during the sonographic evaluation of the fetus or during the evaluation of the pregnant woman who is experiencing renal colic. The fetus is at the highest risk from radiation exposure from the preimplantation period to approximately 15 weeks’ gestation. Because the radiation dose that is associated with congenital malformations is 10 cGy, the evaluation of renal colic in a pregnant patient is performed usually with sonography (radiation dose with abdominal CT: 1 cGy, intravenous pyelogram: 0.3 cGy). The indications for operative intervention in the pregnant patient are discussed elsewhere in this book. Anesthetic risks during pregnancy concern both the mother and the fetus. During the first trimester, the fetus may be directly exposed to the teratogenic effects of certain anesthetic agents. Later in pregnancy, anesthesia places the mother at risk for preterm labor and the fetus at risk for hypoxemia secondary to changes in uterine blood flow and maternal acid base balance. These risks seem to be greatest during the first and third trimesters. For semielective procedures, an attempt should be made to delay surgery until after the first trimester. However, one must consider the continued exposure of the underlying condition in relation to the operative risks to both the mother and the fetus. The second trimester is the safest time to perform surgery because organ system differentiation has occurred and there is almost no risk for anesthetic-induced malformation or spontaneous abortion. When contemplating surgery on the pregnant female, consultation with the obstetrician, perinatologist, and anesthesiologist is essential. These specialists will help determine the optimum technique to monitor the status of the fetus in the pregnant mother. Fetal heart rate monitors and tocometer monitoring for uterine activity are used before and after the procedure. Postoperative pain is best managed with narcotic analgesics because they have not been shown to cause birth defects in humans when used in normal dosages. Nonsteroidal anti-inflammatory medication should be avoided because of the risk for premature closure of the ductus arteriosus. Chronic use of narcotics during pregnancy may cause fetal dependency, and it is recommended that the pregnant postsurgical patient be weaned off narcotic use as soon as possible (Mikami et al, 2008).

Nutritional Status

Malnutrition compromises host defenses and increases the risk of perioperative morbidity and mortality. Adequate nutritional status is essential for proper wound healing, management of infections, return of gastrointestinal activity, and maintenance of vital organ function (McDougal, 1983). The preoperative evaluation of the patient’s nutritional status consists of the assessment of any recent weight loss and the measurement of the lymphocyte count and serum albumin. A 20-pound weight loss in the preceding 3 months before surgery is considered to be a reflection of severe malnutrition. The lymphocyte count and serum albumin level reflect visceral protein status with lower levels indicating malnutrition (Reinhardt et al, 1980). There are two methods for nutritional support. Total parenteral nutrition (TPN) is used for patients who are severely malnourished and who have a nonfunctioning gastrointestinal tract. Several studies have shown that 7 to 10 days of preoperative parenteral nutrition improves postoperative outcome in undernourished patients (Von Meyenfeldt et al, 1992). On the contrary, its use in well-nourished or mildly undernourished patients is either of no benefit or even with increased risk of sepsis (Perioperative total parenteral nutrition in surgical patients, 1991). On the other hand, enteral nutrition has a fewer complications than TPN and can provide a more balanced physiologic diet. Elemental nutrition is accomplished via a feeding tube, a gastrostomy, or feeding jejunostomy. Enteral nutrition maintains the gut-associated lymphoid tissue, enhances mucosal blood flow, and maintains the mucosal barrier. There are hundreds of enteral products on the market, and most have a caloric density of 1 to 2 kcal/mL. These formulas are also lactose free and provide the recommended daily allowances of vitamins and minerals in less than 2 L per day. The patients on enteral feeds must be monitored for improvement in nutritional status, gastrointestinal intolerance, and fluid and electrolyte imbalance. Preoperative enteral feedings can decrease postoperative complication rates by 10% to 15% when used for 5 to 20 days before surgery (Guidelines, 2002). The guidelines recommend postoperative parenteral nutrition in patients who are unable to meet their caloric requirements within 7 to 10 days. Just as in the perioperative state, enteral feedings are preferred over parenteral nutrition when feasible. Moreover, the routine use of postoperative TPN has not proven useful in well-nourished patients or in those with adequate oral intake within 1 week after surgery (Byers and Hameed, 2008). Complications can occur with either enteral nutrition or parenteral nutrition. Dislodgement of nasoenteral tubes and percutaneous enteral catheters can result in pulmonary and peritoneal complications. Adynamic ileus may also occur because of decreased splanchnic perfusion, sympathetic tone, or opiate use. With regards to TPN, establishing central access is associated with a significant risk of complications. These include pneumothorax/hemothorax secondary to poor line placement and chylothorax secondary to thoracic duct injury. Line sepsis is the most common complication of indwelling central catheters and necessitates catheter removal. Venous thrombosis with associated thrombophlebitis and extremity edema has been reported. Catheter thrombosis has also been reported and can be treated with thrombolytic agents (Guidelines, 2002).

Antibiotic Prophylaxis

In 1999 the Centers for Disease Control (CDC) issued its third report on the prevention of surgical site infections (SSIs) highlighting the importance of standardization of prophylaxis treatment to prevent this universal surgical complication (Mangram et al, 1999). The report indicated that SSIs account for approximately 40% of nosocomial infections in surgical patients and potentially prolong hospital stay by 7 to 10 days. A study of national SSIs from the 2005 Healthcare Cost and Utilization Project National Inpatient Sample (HCUP NIS) calculated an increase in hospital stay of 9.7 days and in per-patient cost of $20,892 (de Lissovoy et al, 2009). This translated nationally into an additional 1 million inpatient hospital days and additional health care cost of $1.6 billion. Bowater and colleagues recently published a systematic review of meta-analyses (level 1 evidence) and concluded that there was substantial evidence that antibiotic prophylaxis was an effective prevention for SSI over a wide variety of surgical procedures (Bowater et al, 2009). Given both the ethical responsibility of the surgeon to decrease surgical morbidity and the recent policy shift by the Centers of Medicare and Medicaid Services to withhold reimbursement for hospital admissions secondary to specific SSI, it is mandatory for urologists to understand the principles behind and practice SSI prevention.

Along with antibiotic prophylaxis, proper hand washing/scrubbing and sterile preparation of the operative field have always been central to the prevention of SSI. For procedures involving the gastrointestinal tract, mechanical and oral antibiotic bowel preparation had been standard practice until more recent literature calling into question its usefulness (discussed later). Preoperative hair removal has not been associated with a decrease in SSI, but if performed, use of mechanical clippers or depilatory creams as opposed to razors are associated with a decrease risk of SSI (Wolf et al, 2008).

The risk of SSI and therefore the recommendation for antibiotic prophylaxis is composed of three risk factors: the patient’s susceptibility to and the ability to respond to localized and systemic infection, procedural risk of infection, and the potential morbidity of infection. Patient-related factors, listed in Table 6–4, increase risk by decreasing natural defenses, increasing the local bacterial concentration, and/or altering the spectrum of bacterial flora. Secondly, surgical procedure–specific factors can affect the route of entry, site of infection, and pathogen involved. This idea was first described in the landmark study from the National Research Council and later formalized by the CDC; specifically, surgical wounds are now classified by degree of contamination (i.e., the inoculum of potential pathogen) (Table 6–5; Hart et al, 1968). To predict the risk of SSI, several scoring systems have been developed incorporating patient-related factors with wound classification. Finally, the risk to the patient from SSI is an important consideration in determining the need for prophylaxis. For example, routine cystoscopy in the evaluation of microhematuria in an otherwise young, healthy patient may not warrant prophylaxis; however, the same procedure in an elderly, insulin-dependent diabetic (immunocompromised) does warrant prophylaxis given the high likelihood that a postprocedural urinary tract infection would result in a significant deterioration in the patient’s overall health. Understanding the three factors together then allows the urologist to make a rational decision as to the risk/benefit of antibiotic prophylaxis.

Table 6–4 Patient Factors That Increase the Risk of Infection

Table 6–5 Surgical Wound Classification

Once the decision for antibiotic prophylaxis is made, the keys to successful prevention are proper timing and administration of the antibiotic and the proper choice of antibiotic for the particular procedure. Since the pivotal study by Classen and colleagues, particular emphasis has been placed on the timing of prophylaxis to be given within 2 hours of incision (Classen et al, 1992

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