M ORE than 13 million units of red blood cells (RBC) are collected in the United States and over 1 1 million units are transfused to 3.4 million patients annually. It is estimated that 60 70% of these RBC units are transfused in the perioperative period. Such considerable numbers are in sharp contrast with the little knowledge we have on the true benefits of ery throcyte transfusions. In this refresher course lecture, we will discuss the risks of anemia and the benefits of RBC transfusions in the perioperative context. For a more detailed and formal review of the literature, the reader is referred to a recently published text by the same authors. 1 Conceptually, the risk/benefit ratio of erythrocyte transfusions must take three factors into account: 1) the risks secondary to anemia which depend, in turn, on the patient's capacity to compensate for it; 2) the capacity of allogeneic RBC to correct these risks, a consideration which is all too often assumed but has not been well demonstrated; 3) the risks of transfusions themselves. While the infectious risks of blood products, specially HIV, have brought about a major reconsideration of the way we should be administering transfusions, the risks associated with the immunomodulating effects of blood products, as well as the "classic" complications (volume overload, ABO incompatibility, etc.) of RBC transfusions should be kept in mind. Given the inherent complexity of this risk/benefit analysis, it becomes rapidly apparent that any attempt to define a universal "transfusion trigger" is overly simplistic and unrealistic from a scientific standpoint. The analogy with a "fever trigger" illustrates why the attempt to define a "transfusion trigger" is doomed to fail clinically. Attempting to define a "fever trigger", i.e., the fixed body temperature above which penicillin should be administered would, nowadays, be consid ered absurd. Yet, this is the approach adopted by sever al when transfusing RBC. Erythrocytes (penicillin) are administered for anemia (fever) without knowing if the underlying disease will respond to the elected therapeu tic approach. Adopting a universal "fever trigger" would certainly cure a few individuals, but would need lessly expose a considerable number of patients to peni cillin and result in a significant number of untoward events, allergic or other. Erythrocyte transfusions: the arguments In contrast with the paucity of objective data on the risks of anemia or the benefits of RBC transfusions, several arguments have been put forward either to support or to condone erythrocyte transfusions in the perioperative period. RaHonale in favour of IP~BC transfusions to maintain a high hemoglobin concentvaHon Classically, several arguments have supported the use of RBC transfusions to maintain a high hemoglobin concentration ([Hb]" above 100 g.L 1). • Transfusions are thought to be safer than ever. While this is true in part, the growing concern in Europe with new variant Creutzfeldt Jakob disease illustrates how fragile the situation really is. 2 • Increased 0 2 delivery may improve survival in the intensive care setting. Yet, it remains unclear if the best way to achieve increased 02 delivery is by increasing cardiac output or by increasing [Hb]. • Patients with cardiovascular disease may not be able to compensate for anemia and a high [Hb] will decrease the risk of morbidity and mortality. • Similarly, advanced age, disease and drugs will diminish the adaptation to anemia and a high [Hb] will decrease the risk of morbidity and mortality. • A high [Hb] is required for optimal hemostasis. The contribution of RBC to coagulation is impor tant and all too often overlooked. • A high [Hb] will restore peripheral blood volume and decrease the risks associated with under perfu sion of the gastrointestinal tract. • A high [Hb] will improve the margin of safety, should further bleeding occur. • Finally, a high [Hb] is associated with improved From the Departments of Anesthesiology, Centre Hospitalier de l'Universit6 de Montr6al and Institut de CaJdiologie de Montr6al, Universit6 de Montr6al, Montreal, Quebec, Canada. Address correspondence to'. Dr. Jean Francois Hardy, CHUM HOtel Dieu de Montreal, Pavillon de Bouillon, local 6 521, 3840 me St Urbain, Montreal, Quebec, Canada H2W 1T8. Phone: 514 8908000, ext. 15578; Fax: 514 412 7143; E mail: jean francois.hardy@umontreal.ca CAN J ANESTH 2001 / 48:6 / pp R1 R7