Body Mass Index: Surgical Site Infections and Mortality after Lower Extremity Bypass from the National Surgical Quality Improvement Program 2005-2007

Background: Patients undergoing lower extremity bypass are at high risk for surgical site infections (SSI). We examined lower extremity bypasses by graft origin and body mass index (BMI) classification to analyze differences in postoperative mortality and SSI occurrence. Methods: The 2005-2007 National Surgical Quality Improvement Program (NSQIP), a multi-institutional risk-adjusted database, was queried to compare perioperative mortality (30-day), overall morbidity, and SSIs after lower extremity arterial bypass for peripheral arterial disease. Bypass was stratified by graft origin as aortoiliac, femoral, or popliteal. Patient demographics, comorbidities, operative, and postoperative occurrences were analyzed. Results: There were 7,595 bypasses performed (1,596 aortoiliac, 5,483 femoral, and 516 popliteal). Mortality was similar regardless of bypass origin (2.8%, 2.4%, and 2.7%; p = 0.57). SSIs occurred in 11% of overall cases (10%, 11%, and 11%; p = 0.47). Graft failure was significantly associated with postoperative SSI occurrence (odds ratio [OR] 2.4, 95% confidence interval [CI] 1.9-3.1, p < 0.001), as was postoperative sepsis (OR = 6.5, 95% CI 5.1-8.3, p < 0.001). Independent predictors of mortality were age, aortoiliac bypass origin, underweight, normal weight, morbid obesity (compared to overweight and obese), end-stage renal disease, poor preoperative functional status, preoperative sepsis, chronic obstructive pulmonary disease, hypoalbuminemia, and cardiac disease. Independent predictors of SSI were obesity, diabetes, poor preoperative functional status, a history of smoking, and female gender. Conclusion: SSIs occur frequently after lower extremity bypass regardless of bypass origin and are associated with early graft failure and sepsis. Obesity predicts postoperative SSI. Mortality risk was greatest in the underweight, followed by morbidly obese and normal-weight patients, while overweight and mild to moderate obesity were associated with the lowest mortality.