Normalized Lactate Load Is Associated with Development of Acute Kidney Injury in Patients Who Underwent Cardiopulmonary Bypass Surgery

Background and Objective Cardiac surgery associated acute kidney injury is a major postoperative complication and has long been associated with adverse outcomes. However, the association of lactate and AKI has not been well established. The study aimed to explore the association of normalized lactate load with AKI in patients undergoing cardiac surgery. Methods This was a prospective observational cohort study conducted in a 47-bed ICU of a tertiary academic teaching hospital from July 2012 to January 2014. All patients undergoing cardiopulmonary bypass surgery were included. Normalized lactate load (L) was calculated by the equation: L = 1/2x(t(n)-t(0)) Sigma(n)(i=0)(v(i) + v(i+1)) x (t(i+1)-t(i)), where t(i) was time point for lactate measurement and v(i) was the value of lactate. L was transformed by natural log (L-ln) to improve its normality. Logistic regression model was fitted by using stepwise method. Scale of L-ln was examined by using fractional polynomial approach and potential interaction terms were explored. Results A total of 117 patients were included during study period, including 17 AKI patients and 100 non-AKI patients. In univariate analysis L-ln was significantly higher in AKI as compared with non-AKI group (1.43 +/- 0.38 vs 1.01 +/- 0.45, p = 0.0005). After stepwise selection of covariates, the main effect logistic model contained variables of L-ln (odds ratio: 11.1, 95% CI: 1.22-101.6), gender, age, baseline serum creatinine and fluid balance on day 0. Although the two-term fractional polynomial model was the best-fitted model, it was not significantly different from the linear model (Deviance difference = 6.09, p = 0.107). There was no significant interaction term between L-ln and other variables in the main effect model. Conclusions Our study demonstrates that L-ln is independently associated with postoperative AKI in patients undergoing CPB. There is no significant interaction with early postoperative fluid balance.