Homologous Blood, Salvaged Blood, or no Transfusion?

Abstract

The question of whether to transfuse at all comes before the question of whether to use autologous versus homologous blood. Until recently, a hemoglobin level of 10 g/dL was considered the lowest acceptable level for a patient undergoing surgery. {1} There is now good evidence that this “action level” is too high. Indeed, oxygen delivery to the tissues is enhanced by a modest degree of anemia provided the patient can maintain an increased cardiac output. This is because the viscosity of whole blood is largely dependent upon the volume of red cells that it contains. High hematocrit blood can deliver increased oxygen to the tissues only if it can be moved swiftly through the microcirculation; and the high viscosity of such blood guarantees a prolonged circulation time. Why then does Mother Nature equip us with a hematocrit of 45 when there are so many physiological advantages that accrue when the hematocrit drops to 25? The answer is that most of us are upright and exercising large muscle groups most of the time. We are not resting quietly, lying in bed following major surgery. During vigorous physical activity a reserve capacity for oxygen transport is very helpful. Some athletes have received a one or two unit transfusion of their own blood just before competition for this very reason. Other athletes practice their sport at high altitude to achieve the same result.