Anemia in critical illness.

Anemia is a frequent finding in patients treated in ICUs and results in a high number of red blood cell transfusions. Many patients are already admitted to ICUs with subnormal hemoglobin values. Surgery, frequent phlebotomies and overt bleeding episodes are obvious reasons for continuous blood loss during the ICU stay. However, these causes are usually not sufficient to explain the total blood consumption of critically ill patients, which may amount to several liters. Reduced red cell life span and occult gastrointestinal bleeding are possibly important contributory factors. Irrespective of the cause the erythropoietic response to anemia is severely blunted, as a consequence of an inappropriate increase in erythropoietin production, diminished iron availability and direct inhibitory effects of inflammatory cytokines. The importance of anemia for the course and outcome of critically ill patients and its optimal therapy remain to be defined. Considering red blood cell transfusions recent evidence indicates that a target range of 7-9 g/dl hemoglobin is at least as safe and may even be superior compared to a more liberal transfusion strategy. However, the optimal transfusion trigger in relation to patient comorbidity requires further investigation. Rigorous strategies of blood conservation may help to avoid transfusions. Red blood cell substitutes and recombinant erythropoietin are promising treatment options that are currently under investigation.