Scope of the problem: epidemiology of anemia and use of blood transfusions in critical care

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Abstract
Anemia is a common problem in critically ill patients. It is caused, in part, by blood loss related to phlebotomy for diagnostic testing, occult gastrointestinal bleeding, renal replacement therapies, surgical intervention, and traumatic injuries. Reduced red cell life span and nutritional deficiencies (iron, folate, vitamin B12) may be other contributing factors. In addition, critically ill patients have impaired erythropoiesis because of blunted endogenous erythropoietin production and the direct inhibitory effects of inflammatory cytokines on red blood cell production by the bone marrow. Blood transfusions are commonly utilized for treatment of anemia in critical care, resulting in high use of blood transfusions in the intensive care unit (ICU). The percentage of patients transfused in the ICU is inversely related to admission hemoglobin and directly related to age and severity of illness. Patients with an increased length of stay in the ICU are also at increased risk for receiving blood transfusions. Studies are needed to improve our understanding of the pathophysiology of ICU-acquired anemia, to determine the efficacy of blood transfusions in critical care, and to investigate alternatives to blood transfusion for the treatment of anemia in the ICU.