[Tolerance to perioperative anemia. Mechanisms, influencing factors and limits].

The expected cost explosion in transfusion medicine increases the socio-economic significance of specific institutional transfusion programs. In this context the estimated use of the patient's physiologic tolerance represents an integral part of any blood conservation concept. The present article summarizes the mechanisms, influencing factors and limits of this natural tolerance to anemia and deduces the indication for perioperative red blood cell transfusion. The current recommendations coincide to the effect that perioperative transfusion is unnecessary up to a Hb concentration of 10 g/dl (6.21 mmol/l) even in older patients with cardiopulmonary comorbidity and is only recommended in cases of Hb <6 g/dl (<3.72 mmol/l) in otherwise healthy subjects including pregnant women and children. Critically ill patients with multiple trauma and sepsis do not seem to benefit from transfusions up to Hb concentrations >9 g/dl (>5.59 mmol/l). In cases of massive hemorrhaging and diffuse bleeding disorders the maintenance of a Hb concentration of 10 g/dl (6.21 mmol/l) seems to contribute to stabilization of coagulation.