BMI*VFA/SFA: a new measure for obesity as risk factor for postoperative complications in colorectal surgery.

Purpose: Colorectal cancer is a common malignancy in the Netherlands, with 12.000 new cases annually. In recent years safety and risks of colorectal surgery have been studied extensively. Obesity is considered an important risk factor, but most studies fail to find significant relations between obesity and postoperative complications. The majority of these studies use BMI as measure of obesity. BMI does not discriminate between subcutaneous and visceral fat. Only the latter is related to the metabolic syndrome, which identifies the centrally obese patient with increased risk for cardiovascular disease and diabetes mellitus. Our aim is to investigate whether BMI multiplied by visceral fat area / subcutaneous fat area ratio (VFA/SFA) is a valuable new measure for obesity, better related to postoperative complications. Secondarily we investigated whether a higher BMI*VFA/SFA was also related to prolonged operation time and lower survival. Methods: A retrospective chart review was conducted in 85 patients who were surgically treated for colorectal cancer. VFA/SFA was determined using 20 consecutive CT-slices of 1 mm cranial to the iliac crest. Severe complications were defined as IIIa or higher according to Clavien-Dindo classification. BMI, VFA/SFA and BMI*VFA/SFA were used as obesity measures and related to severe complications and survival and correlated to operation time. Results: The only variables significantly related to severe postoperative complications were hypertension and BMI*VFA/SFA. In multivariate analysis only BMI*VFA/SFA continued to be a significant explaining factor (OR 1,06; 95% CI: 1,01-1,12). Operation time was not significantly correlated to any of the obesity measures. Obese patients eighter defined as BMI >30 and BMI*VFA/SFA > 50th percentile showed significant lower 3-year cumulative disease-free-survival, respectively P = 0,012 and P = 0,030. Overall survival showed HR of 3,85 (95% CI: 1,18-12,53) for BMI > 30 and HR = 2,75 (95% CI: 0,96-7,73) for BMI*VFA/SFA > 50th percentile. Conclusion: BMI*VFA/SFA is the best explaining variable for severe postoperative complications in surgery in patients for colorectal cancer. There was no correlation between operation time and the different obesity measures. Patients who were obese according to BMI and BMI*VFA/SFA showed a significant lower 3-year cumulative disease-free-survival. Prognostic significance of BMI*VFA/SFA as new measure for obesity should be further determined in a prospective study with a larger population.