Red cell transfusion therapy in the critical care setting.

According to our own experience and published reports the frequency of red cell transfusion in intensive care units is in the range of 0.2 to 0.4 units per patient per day and is dependent upon the local strategy, the patients involved and the kind of surgery performed. The rationale for red cell transfusion is to maintain or restore the oxygen carrying capacity of the blood to avoid tissue hypoxia which occurs when oxygen delivery drops below a certain critical value. Besides bleeding, phlebotomy is also a significant source of blood loss in critically ill patients. According to several recent reviews and consensus articles there is no basis for a fixed indicator for transfusion, such as a haemoglobin concentration of < 100 gL-1. The decision to transfuse has to be made according to the patients individual status. The major adaptive mechanism in response to acute anaemia is an increase in cardiac output and hence blood flow to tissues. As a consequence even moderate degrees of acute anaemia may not be tolerated by patients with cardiac disease, whilst marked anaemia carries a considerable risk of ischaemia in patients with brain lesions or cerebral arterial stenoses. In critically ill patients it has been postulated that supply dependency of oxygen consumption occurs over a wide range of oxygen delivery, far above the critical values of oxygen delivery seen under normal conditions. Maximising oxygen delivery was therefore formulated as a goal in these patients. However, whether pathological supply dependency of oxygen delivery really exists in critically ill patients is still under discussion and recent studies found no benefit in maximising oxygen delivery to this patient group. However, individualised triggers for red blood cell transfusion are adequate for critically ill patients considering their co-morbidities and severity of disease. Finally, the decision to transfuse must also take into account the potential risks (infectious and non-infectious), as well as benefits for the individual patient. In the future, the level of transfusions may be reduced by using blood sparing techniques such as blood withdrawal in closed systems, bedside microchemistry, intravascular monitors, or autotransfusion of drainage blood in intensive care units.