The most widely used classification of obesity is the body mass index (BMI).1 Between 1986 and 2000, the number of individuals with BMIs greater than 30, 40, and 50 kg/m2 were reported to have doubled, quadrupled, and quintupled, respectively, in the United States.2
Obesity has long been considered to be a risk factor for poor outcomes from a variety of surgical procedures, yet recent studies of critically and chronically ill patients suggested that overweight and obese patients may paradoxically have better outcomes than “normal”-weight patients.3 Mullen et al.3 demonstrated, in a prospective multi-institutional risk-adjusted study of 118,707 patients undergoing nonbariatric surgery, that the highest rates of death occurred in the underweight and morbidly obese, and the lowest rates were found in the overweight and moderately obese patients. This study revealed that there was a progressive increase in the likelihood of a complication with increasing BMI that was almost entirely due to increasing rates of infection. They hypothesized that metabolic regulation and immune response are highly integrated. Malnourished patients have protein calorie malnutrition, which impairs immunologic response mechanisms; obese patients are known to have a low-grade inflammatory response, which primes their immune system.3
PREOPERATIVE EVALUATION AND PREPARATION
Despite emerging evidence of the “obesity paradox,” there are recommendations for the preoperative evaluation and preparation of obese patients. The extent of the preoperative evaluation depends on the assessment of their surgical risk and the degree of surgery-specific risk.
Major surgery is accompanied by an increased demand for oxygen consumption. This places increased demands on the cardiorespiratory system.4 If patients are unable to increase their oxygen delivery to meet these requirements, they have increased mortality.5
Patient Preoperative Surgical Risk
Preoperative risk assessment always starts with an in-depth history and comprehensive physical examination. Will the patient be able to tolerate the physiological stresses of the planned surgery? The American College of Cardiology and American Heart Association (ACC/AHA) have established clinical predictors of cardiac risk. Patients can be categorized as having minor, intermediate, and major risks. However, a more important predictor of risk is the patient’s functional capacity. This assessment helps us understand how combined cardiopulmonary function will tolerate the stress of surgery. This can be readily ascertained using a simple set of questions adopted from the Duke Activity Status Index. This concept measures a patient’s physiologic response by determining the metabolic equivalent tasks (METs). One MET is 3.5 mL/min/kg average resting oxygen consumption in a 70-kg, 40-year-old man.4 The ACC/AHA guidelines state the patients with exercise tolerance of greater than 4 METs may proceed to major surgery without further investigation.4 Patients with poor exercise tolerance (<4 METs) have significantly greater cardiovascular and neurological complication (20.4% vs. 10.4%, p < 0.001).6