Controversies related to red blood cell transfusion in critically ill patients

Objective – To review the evolution of and controversies associated with allogenic blood transfusion in critically ill patients. Data sources – Veterinary and human literature review. Human Data Synthesis – RBC transfusion practices for ICU patients have come under scrutiny in the last 2 decades. Human trials have demonstrated relative tolerance to severe, euvolemic anemia and a significant outcome advantage following implementation of more restricted transfusion therapy. Investigators question the ability of RBCs stored longer than 2 weeks to improve tissue oxygenation, and theorize that both age and proinflammatory or immunomodulating effects of transfused cells may limit efficacy and contribute to increased patient morbidity and mortality. Also controversial is the ability of pre‐ and post‐storage leukoreduction of RBCs to mitigate adverse transfusion‐related events. Veterinary Data Synthesis – While there are several studies evaluating the transfusion trigger, the RBC storage lesion and transfusion‐related immunomodulation in experimental animal models, there is little research pertaining to clinical veterinary patients. Conclusions – RBC transfusion is unequivocally indicated for treatment of anemic hypoxia. However, critical hemoglobin or Hct below which all critically ill patients require transfusion has not been established and there are inherent risks associated with allogenic blood transfusion. Clinical trials designed to evaluate the effects of RBC age and leukoreduction on veterinary patient outcome are warranted. Implementation of evidence‐based transfusion guidelines and consideration of alternatives to allogenic blood transfusion are advisable.