Perioperative Bleeding Is Not an Independent Risk Factor for Acute Kidney Injury in On-pump Cardiac Surgery—A Post-hoc Analysis of a Randomized Clinical Trial

Objectives: To study the association between bleeding and acute kidney injury (AKI). Design: Post-hoc study of a randomized trial of 4% albumin versus Ringer's acetate for cardiopulmonary bypass priming and perioperative volume replacement. Setting: Single-center study. Patients: 1,386 on-pump cardiac surgical patients. Measurements and Results: AKI was defined by the Kidney Disease: Improving Global Outcomes creatinine criteria, and bleeding by the Universal Definition of Perioperative Bleeding (UDPB) classification. With univariably independent factors, two logistic regression analyses (Model 1: AKI Risk Score, EuroSCORE II, and UDPB class; Model 2: risk scores, components of the UDPB classification, and factor VIII/von Willebrand factor concentrate) and a mediation analysis (Model 3: risk scores, UDPB class, and perioperative factors) were performed. A total of 139 (10%) patients developed AKI. In Model 1, UDPB class “severe” (odds ratio: 2.16, 95% confidence interval: 1.19-3.89), “massive” bleeding (6.78, 1.8-25.33), and AKI Risk Score (1.51, 1.29-1.78) were associated with AKI. In Model 2, AKI Risk Score (1.55, 1.33-1.82) and fresh frozen plasma transfusion (1.29, 1.06-1.58) were associated with AKI. In Model 3, the combined UDPB classes “severe” and “massive” bleeding did not have a direct effect (regression coefficient: 0.32, 95% confidence interval: –0.26 to 0.91), while mean arterial pressure (0.08, 0.003-0.21) and fluid balance (0.12, 0.17-0.27) had indirect effects on AKI. Conclusions: In on-pump cardiac surgery, perioperative bleeding was not an independent risk factor for AKI but manifested as AKI via hypotension and higher fluid balance. Prevention of bleeding may reduce AKI in cardiac surgery.