Hyperthermic perfusion during cardiopulmonary bypass and postoperative temperature are independent predictors of acute kidney injury following cardiac surgery

Acute kidney injury (AKI) following cardiopulmonary bypass (CPB) is associated with increased mortality, requirement for dialysis, and longer intensive care unit (ICU) and hospital length of stay. Rewarming during CPB and poor oxygen delivery have been associated with AKI; however, the role of temperature management on AKI has not been clearly defined. This study aims to evaluate the role of hyperthermia during CPB and the temperature upon admission to the ICU on AKI following cardiac surgery, using the RIFLE (renal Risk, Injury, Failure, Loss of renal function and End-stage renal disease) criteria. To determine whether CPB hyperthermia (measured as the cumulative time the arterial outlet temperature >37°C) and ICU admission temperature were independent risk factors for AKI, data from 1393 consecutive adult patients undergoing isolated on-pump coronary artery bypass graft (CABG), valve repair and/or replacement and valve/CABG procedures was analysed using a logistic multivariate model. After testing for interaction, we incorporated covariates having a p-value <0.1. AKI was defined according to the RIFLE criteria as an increase in serum creatinine >50% from baseline to peak value postoperatively. Overall, 12.3% of patients developed AKI with a 4.5-fold increase in in-hospital mortality. Variables found to be independent predictors of AKI included CPB hyperthermia (Odds ratio [OR] 1.03 per minute increase [95% confidence interval (CI) 1.01-1.05]; p = 0.01), ICU admission temperature ([OR] 1.44 per degree increase [(CI) 1.13-1.85]; p<0.001), minimum CPB haemoglobin ([OR] 0.83 per g/dL increase [(CI) 0.71-0.97]; p = 0.02), use of intra-aortic balloon pump ([OR] 2.69 [(CI) 1.24-5.82]; p = 0.01) and ICU readmission ([OR] 3.13 [(CI) 1.73-5.64]; p<0.001). Avoiding arterial outlet hyperthermia may help decrease AKI following cardiac surgery using CPB. Both intraoperative and postoperative temperature management strategies should be the focus of future randomised studies to determine optimal interventions.