Risks of transfusion in patients with preoperative anemia requiring cardiac surgery

INTRODUCTION: Preoperative anemia is common and a strong predictor of perioperative red blood cell (RBC) transfusion in cardiac surgical patients. Both anemia and RBC transfusion are independently associated with adverse postoperative outcomes, but their interrelationship is difficult to disentangle because RBC transfusion acts as a mediator rather than a confounder. AREAS COVERED: This narrative review summarizes current evidence on the relationship between preoperative anemia, RBC transfusion, and postoperative outcomes in cardiac surgery, with particular emphasis on recent advances in causal inference mediation analysis. We discuss outcome-specific mediation patterns, patient characteristics that may modify anemia and transfusion related risk, and implications for perioperative management. EXPERT OPINION: Mediation analysis provides a valuable framework for distinguishing the direct effects of anemia from RBC transfusion-mediated effects. Current evidence suggests that RBC transfusion mediates a substantial proportion of anemia-associated mortality, whereas direct anemia effects appear more important for renal complications. Future patient blood management should move beyond uniform transfusion thresholds toward individualized strategies that account for patient's risk profile, physiological reserve, intraoperative factors and the outcome-specific balance between the potential benefits of correcting anemia and the risks of RBC transfusion.