Obesity: an independent predictor of in-hospital postoperative renal insufficiency among patients undergoing cardiac surgery?

Abstract

We sought to determine, retrospectively, whether obesity was associated with adverse renal outcomes in 17,630 patients who underwent cardiac surgery from January 1995 through December 2006. Obesity was defined as a body mass index > or = 30 kg/m2. The primary outcome was any episode of postoperative renal insufficiency (requiring or not requiring dialysis) before hospital discharge. Outcomes were evaluated in the entire cohort and in subgroups undergoing isolated coronary artery bypass grafting (CABG), isolated valve surgery, and combined CABG and valve surgery. The final analysis included 16,429 patients, 5,124 (31%) of whom were obese. In the entire cohort, obesity was associated both with increased risk of any postoperative renal insufficiency (odds ratio [OR], 1.37; 95% confidence interval [CI], 1.21-1.55) and with increased risk of renal insufficiency not requiring dialysis (OR, 1.41; 95% CI, 1.23-1.62). Obesity was associated with an increased risk of postoperative renal insufficiency in patients undergoing isolated CABG (OR, 1.38; 95% CI, 1.18-1.61), isolated valve surgeries (OR, 1.39; 95% CI, 1.05-1.85), and combined CABG and valve surgeries (OR, 1.35; 95% CI, 0.99-1.83; statistically nonsignificant). Development of postoperative renal insufficiency was associated with a significantly higher mortality rate (P <0.0001) and with a significantly longer hospital stay (23 vs 10.5 days; P <0.0001). We conclude that obesity is associated with a significant increase in postoperative renal insufficiency in cardiac surgery patients, an effect that we attribute to an increase in postoperative renal failure that does not require dialysis.

Keywords: Body mass index; cardiac surgical procedures/adverse effects; cardiopulmonary bypass/adverse effects; inflammation/complications; kidney failure/etiology; obesity/complications; oxidative stress; postoperative complications; retrospective studies; risk factors; systemic inflammatory response syndrome; treatment outcome.

Fig. 1. Characteristics independently associated with postoperative renal insufficiency during hospitalization after cardiac surgery in our entire study population of 16,429 patients.^* CABG = coronary artery bypass grafting; CI = confidence interval; CVA = cerebrovascular accident; IABP = intra-aortic balloon pump; PVD = peripheral vascular disease ^*Includes variables significantly associated with postoperative renal insufficiency after multivariate regression analysis.

Fig. 2. Characteristics independently associated with postoperative renal insufficiency after propensity-score matching in 6,866 patients (3,433 obese and 3,433 nonobese).^* CABG = coronary artery bypass grafting; CI = confidence interval; IABP = intra-aortic balloon pump; PVD = peripheral vascular disease ^*Results obtained by multivariate regression analysis after propensity-score matching (n = 6,866 patients). Please see text in Methods section as well as Table I for list of variables matched for propensity-score analyses.