The association of body mass index to postoperative outcomes in elderly vascular surgery patients: a reverse J-curve phenomenon.

BACKGROUND: The purpose of this investigation was to determine whether there is a relation between body mass index (BMI) classes and early postoperative outcomes in elderly patients undergoing vascular surgery. We hypothesized that being overweight or obese increases the risks of surgery.
METHODS: Data from the American College of Surgeons' National Surgical Quality Improvement Program Participant Use Data File was used to identify the BMI (kg/m(2)) and 30-day outcomes of 25,337 patients aged ≥ 65 years undergoing vascular surgery from 2005 to 2007. Patients were stratified into 6 BMI classes: (1) underweight (BMI ≤ 18.5 kg/m(2)), (2) normal (BMI = 18.6-24.9 kg/m(2)), (3) overweight (BMI = 25-29.9 kg/m(2)), (4) obese class I (BMI = 30-34.9 kg/m(2)), (5) obese class II (BMI = 35-39.9 kg/m(2)), and (6) obese class III (BMI ≥ 40 kg/m(2)). Morbidity and mortality rates across all BMI classes were subjected to univariate and multiple logistic regression analyses.
RESULTS: Mortality rates varied among the BMI classes: 9.4% underweight, 4.0% normal, 3.0 overweight and obese I, 3.3% obese II, and 4.6% obese III (P < 0.001). Major postoperative morbidity paralleled the risk of death. Independent preoperative factors associated with mortality included diabetes mellitus, chronic obstructive pulmonary disease, active congestive heart failure, recent weight loss, disseminated cancer, and an inability to function independently. Each of these factors was statistically more important than the BMI alone in defining an increased risk of surgery.
CONCLUSION: Increased BMI alone was not a major factor predicting perioperative 30-day mortality in this cohort of elderly surgical patients; the effect was a nonlinear one with a reversed J-curve response documenting the poorest outcomes in underweight, normal, and a slight increase in excessively obese patients.