Effect of off-pump coronary artery bypass graft surgery on postoperative acute kidney injury and mortality*

Risk of mortality after cardiac surgery is associated with severity of acute kidney injury. The aim of this study is to examine the effect of off-pump coronary artery bypass surgery on the risk of postoperative acute kidney injury and its association with mortality.Observational cohort study.Tertiary care center.Some 10,061 patients underwent coronary artery bypass surgery (1998-2002), of which 1,365 patients underwent off-pump surgery.Acute kidney injury was defined as either requirement of dialysis or >/=50% decline in postoperative glomerular filtration rate but not requiring dialysis. We compared on- and off-pump surgeries and used propensity score matching to examine the effect of off-pump surgery on acute kidney injury and mortality.We found that 2.6% on-pump and 1.2% off-pump patients developed acute kidney injury requiring dialysis among the 2,370 matched subjects (relative risk, 2.06; 95% confidence interval [CI], 1.36-3.36); 5.0% of on-pump patients suffered a >/=50% decline in glomerular filtration rate compared with 2.5% in off-pump group (relative risk, 2.00; 95% CI, 1.48-2.82). The mortality rate in the matched cohort was 2.3% for on-pump group vs. 0.6% in off-pump group (relative risk, 3.88; 95% CI, 2.29-9.50). Among matched patients with acute kidney injury, the risk of mortality was 13.14 (95% CI, 8.43-30.50) in patients requiring dialysis and 9.33 (95% CI, 4.83-19.00) in those with >/=50% decline in glomerular filtration rate but not requiring dialysis.Off-pump surgery is associated with a lower risk of developing acute kidney injury (regardless of its definition). The risk of mortality is incremental with worsening degrees of acute kidney injury. Lower risk of acute kidney injury may be one of the factors that offer a survival advantage after off-pump surgery.