Obesity is associated with postoperative outcomes in patients undergoing cardiac surgery: a cohort study

Background The purpose of present study was to determine whether obesity was associated with increased adverse outcomes after cardiac surgery. Methods This is a retrospective cohort study from a large international database called the Medical Information Mart for Intensive Care III (MIMIC-III). Patients who underwent cardiac surgery and greater than 18 years old were divided into either nonobese (BMI < 30 kg/m(2)) or obese (BMI >= 30 kg/m(2)). The primary outcome of this study was 28-day mortality from the date of operation. Secondary outcomes included ICU mortality, 1-year mortality, incidence of postoperative atrial fibrillation (POAF), hospital length of stay (HOS_LOS) and ventilation-free days within 28 days (VFD_28). Results Multivariate logistic regression analysis revealed a negative effect of obesity on 28-day mortality, with an adjusted odds ratio (OR) of 1.57 (95% CI 1.14-2.16; p = 0.005). The association remained significant when PSM analysis and double robust analysis with all covariates were performed. In terms of 28-day mortality, the mediating effect of longer ventilation duration on obese patients was noticeable, and the proportion of the effect mediated was 8.2% (95% CI 2.1-25.5%; p = 0.012). Conclusions Among patients with cardiac surgery, obesity is associated with higher 28-day mortality. The longer ventilation duration may have mediated this effect. In future, considering the elevated incidence of the obese patients undergoing cardiac surgery, obesity stat should be included as one of the predictive variables for stratification of perioperative death risk.