Distribution of surgical case start times.

BackgroundSurgical start time (SST) has demonstrated conflicting effects on perioperative outcomes due to confounding factors, such as increased acuity in later SST cases. This study investigated the effect of SST on blood transfusion after gastric bypass surgery, a complication-prone elective surgical procedure.MethodsThis retrospective cohort study included all patients undergoing gastric bypass surgery at a single academic medical center from 2016 through 2021 (n = 299). The primary independent variable was SST (before vs. after 15:00). The primary outcome was blood transfusion. Secondary outcomes included postoperative respiratory failure, length of stay, acute kidney injury, and mortality. The associations between SST and outcomes were investigated with univariate analyses. Multivariate and receiver operating characteristic (ROC) analyses were applied to the primary outcome, adjusting for demographic and operative characteristics.ResultsOn univariate analysis, 15:00–18:43 SST was associated with an increased risk of blood transfusion (relative risk 4.32, 95% confidence interval 1.27 to 14.63, p = 0.032), but not postoperative respiratory failure, acute kidney injury, length of stay, or mortality. On multivariate analysis, the only independent predictor of postoperative blood transfusion was a 15:00–18:43 SST (adjusted odds ratio 4.32, 95% confidence interval 1.06 to 15.96, c-statistic = 0.638). ROC analysis demonstrated that compared to the 15:00 threshold, a 14:34 threshold predicted postoperative blood transfusion with better accuracy (sensitivity = 70.0%, specificity = 83.0%).ConclusionsDespite having similar demographic and operative characteristics, gastric bypass patients in the late SST cohort had a greater incidence of postoperative blood transfusion in this single-center study.