Clinical consequences of anemia and red cell transfusion in the critically ill

Transfusion of packed red cells, a complex biologic product prepared from donated blood, is unique in many respects when compared with other health interventions. Decisions concerning the use of allogeneic red blood cell (RBC) transfusion in the treatment of anemia and hemorrhage require a clear understanding of both the risks and benefits of both the condition and its treatment. Although we have developed a much clearer appreciation for the infectious and immunomodulatory risks of RBC transfusion over the past 2 decades, the risks of anemia in many clinical settings and the benefits of RBC transfusion are still inadequately characterized. We presume that the most significant risk associated with anemia is the harm resulting from the decrease in oxygen carrying capacity and plasma volume. The development of adverse health consequences from anemia will, in part, depend on the capacity of the individual patient to compensate for these changes. The benefit of transfusion refers to the capacity of RBCs to correct these risks and possibly provide additional benefits such as increasing oxygen delivery to supranormal ranges. Such a framework highlights the concept that the tradeoffs of risks and benefits may not be equivalent. With the exception of patients who refuse blood for religious reasons, it is impossible to clearly distinguish between these competing risk and benefits outside a randomized clinical trial.