Identification of modifiable risk factors for acute kidney injury after coronary artery bypass graft surgery in an Asian population

Abstract

Objective: Postoperative acute kidney injury (AKI) after cardiopulmonary bypass (CPB) with coronary artery bypass grafting is common and increases patient morbidity and mortality. Studies have identified the lowest hematocrit during CPB, preoperative anemia, and intraoperative transfusion as modifiable AKI risk factors. Because Asians are smaller in body size, the use of standard CPB circuits can result in excessive hemodilution and subsequent transfusion to maintain the desired hematocrit target of ≥21% during CPB. Thus, we aimed to ascertain whether the lowest hematocrit during CPB, preoperative anemia, and intraoperative transfusion remained as independent modifiable risk factors associated with AKI in our prospective cohort of Asians.

Methods: Data from 1448 patients who had undergone coronary artery bypass grafting with CPB from December 2008 to December 2010 at Singapore's 2 national heart centers were obtained. The perioperative risk factors were analyzed for their associations with postoperative AKI. AKI was defined using the Acute Kidney Injury Network stage 1 criteria.

Results: The incidence of AKI was 27.0% and mean lowest hematocrit during CPB was 24.5% ± 3.8%. The risk of AKI increased with a decreasing lowest hematocrit during CPB (relative risk, 0.933; 95% confidence interval, 0.899-0.968; P < .001), in particular with the lowest hematocrit of ≤22%. A 23% increased risk of AKI was found for preoperative anemia (relative risk, 1.225; 95% confidence interval, 1.022-1.468; P = .028). Intraoperative transfusion was related on univariate analysis (P < .001) but was not independently associated on multivariate analysis (relative risk, 0.961; 95% confidence interval, 0.782-1.180; P = .702).

Conclusions: The lowest hematocrit and preoperative anemia were potentially modifiable risk factors independently associated with AKI after cardiac surgery in our Asian population. Blood transfusion did not affect the development of AKI in our population.