Interrelationship of preoperative anemia, intraoperative anemia, and red blood cell transfusion as potentially modifiable risk factors for acute kidney injury in cardiac surgery: a historical multicentre cohort study.

Purpose: Acute kidney injury (AKI) is a potentially serious complication of cardiac surgery. Anemia and red blood cell (RBC) transfusion have individually been identified as potentially modifiable risk factors, but their interrelationship with AKI has not been clearly defined. The purpose of this study was to explore the interrelationship of preoperative anemia, intraoperative anemia, and RBC transfusion on the day of surgery with AKI in cardiac surgery.
Methods: This historical cohort study included 16 hospitals, each contributing data on approximately 100 consecutive patients who underwent cardiac surgery with cardiopulmonary bypass. Acute kidney injury was defined as a > 50% increase in creatinine levels during the first postoperative week. Multivariable regression was used to identify the interrelationship between preoperative anemia (hemoglobin < 130 g·L(-1) in males and < 120 g·L(-1) in females), intraoperative anemia (hemoglobin < 80 g·L(-1) during cardiopulmonary bypass), RBC transfusion on the day of surgery, and their interaction terms, after adjusting for site and baseline AKI risk.
Results: Of the 1,444 patients included in the study, 541 (37%) had preoperative anemia, 501 (35%) developed intraoperative anemia, 619 (43%) received RBC transfusions, and 238 (16%) developed AKI. After risk-adjustment, an individual with the combination of these three risk factors had a 2.6-fold (95% confidence interval 2.0 to 3.3) increase in the relative risk of AKI over an individual with none of these risk factors.
Conclusions: Preoperative anemia, intraoperative anemia, and RBC transfusion on the day of surgery are interrelated risk factors for AKI after cardiac surgery. Targeting these risk factors may reduce the burden of AKI.