P-38 Linking post-gastric bypass surgery weight loss goals/success to initial bmi

Background: A widely accepted method for estimating weight loss following gastric bypass surgery is percent of excess body mass index (BMI) loss (%EBL). Because the amount of excess body weight is higher in patients with higher BMIs, the %EBL during the postoperative period is commonly lower despite the higher absolute weight loss (i.e., pounds lost); thus patients may be considered failures despite substantial weight loss. We developed a method to standardize weight loss following gastric bypass surgery that accounts for pre-operative BMI. Methods: Roux-en-Y gastric bypass patients with 12 months of post-operative follow-up were included (12 month follow-up rate is 90%). After stratifying by baseline BMI, the distribution of 18-month BMI measures was analyzed to calculate the 10th%tile within each group (i.e. the 10% of patients with the lowest BMI at 18-months). Linear regression was used to create a formula for post-operative BMI using baseline BMI as the independent variable. Results: A total of 1,349 patients (81% female) with a mean age of 46.6 years were studied. Baseline BMI was grouped as 35-39 (n 113), 40-44 (n 342), 45-49 (n 318), 50-54 (n 273), 55-59 (n 144), and 60 (n 159) kg/m. The 10th %tile for 18-month BMI highly correlated with baseline BMI (r-squared 0.9987, pvalue .0001; 18-month BMI 4.564 (0.558*baseline BMI). Conclusion: Establishing %EWL criteria based upon initial BMI as a goal/measure of success, after Roux-en-Y gastric bypass accounts for absolute differences in weight loss across BMI categories. This measure defines an achievable goal for new patients and provides a new standard of post-operative weight loss measurement. More research is needed to validate this measure with co-morbidity resolution and improvement in other health outcomes in a larger, more diverse cohort.