The risks of moderate and extreme obesity for coronary artery bypass grafting outcomes: A study from the Society of Thoracic Surgeons' database

Background. Obesity is epidemic in the United States and afflicts 97 million adults. Prior single center studies have been contradictory as to obese patients having higher risks with coronary artery bypass operations. Our objective was to assess the independent effect of both moderate (body mass index [BMI], 35 to 39.9) and extreme (BMI : 40) obesity on bypass operation outcomes using the Society of Thoracic Surgeons National Cardiac Database. Methods. The study population consisted of 559,004 patients from the Society of Thoracic Surgeons database who underwent first-time, isolated coronary artery bypass grafting between January 1997 and December 2000. We compared 42,060 moderately obese patients (BMI, 35 to 39.9) and 18,735 extremely obese patients (BMI a: 40) with 498,209 normal or mildly obese patients (BMI, 18.5 to 34.9). Multivariable logistic regression was used to determine whether BMI subgroups were independent predictors of operative risk after adjusting for other preoperative factors. Results. Compared with normal or mildly obese patients (BMI, 18.5 to 34.9), moderate and severely obese patients were younger and more likely to be diabetic and hypertensive. After adjusting for these and other known preoperative risk factors, moderate obesity slightly elevated patients' operative risk (adjusted odds ratio, 1.21; confidence interval, 1.13 to 1.29). In contrast, extremely obese patients had marked higher risk for operative mortality (adjusted odds ratio, 1.58; confidence interval, 1.45 to 1.73). Major perioperative complications, particularly deep sternal wound infection, renal failure, and prolonged postoperative hospital stay also increased for extremely obese patients. Conclusions. Extreme obesity (body mass index 2:40) is a significant independent predictor for adverse outcomes and prolonged hospitalization after coronary artery bypass operation.