Assessing the relative contribution of individual risk factors on surgical outcome for gastric bypass surgery: a baseline probability analysis

Abstract

Background: Multiple regression is the best technique for the simultaneous analysis of the contributions of multiple risk factors to a surgical outcome. A probability analysis is used to determine the relative contribution of individual factors to the overall outcome being assessed. We used these techniques to determine which of the potential risk factors had the greatest impact on adverse outcomes following gastric bypass surgery.

Methods: Records from 1067 consecutive patients undergoing Roux-Y gastric bypass at the UCLA Medical Center from December 1993 until June 2000 were reviewed. Major complications were used as the dependent variable in a multivariate logistic regression analysis, and 10 risk factors served as the independent variables. Based on the analysis, an average (i.e., baseline) patient was defined. Variations in the preoperative risk factors were then analyzed individually and in various combinations and their effect on the predicted probability for complication development was assessed.

Results: The overall major complication rate in this series was 5.8%. The average patient was defined as a 334-pound woman who was 42.3 years of age. For this patient, the predicted complication rate by probability analysis was 3.9%. The greatest increase in the anticipated complication rate was attributable to revisional procedures that increased the rate to 6.5%. Many patients have a combination of risk factors; to this end, a 62-year-old, male patient with a 2SD increase in weight (i.e., 464 pounds) who was undergoing a revision operation and had a history of smoking, hypertension, diabetes, and sleep apnea had a predicted complication rate of 33.7%.

Conclusion: Probability analysis is a useful tool for determining the relative contribution of individual and combinations of risk factors for predicting the outcomes for surgical procedures. The four most influential factors for predicting a complication after gastric bypass surgery were; (1) male gender, (2) revisional surgery, (3) increasing age, and (4) increasing weight. These factors increased the predicted complication rate by 56, 67, 28 and 28%, respectively.