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- The current practice of transfusion in the ICU is conservative, reflecting a balance between the benefits and adverse consequences of transfused blood.
- Anemia developing in the ICU should not be attributed solely to phlebotomy; red cell loss, destruction, or underproduction should also be considered.
- Evaluation of the basis for anemia, beginning with analysis of the blood smear, reticulocyte count, and red cell indices, may lead to easier management of the anemia and may prove useful in overall treatment.
- For most critically ill patients, a transfusion target for hemoglobin of 7 to 9 g/dL is at least as safe as a higher threshold of 10 to 12 g/dL; the lower value may be superior.
- Transfusion is rarely associated with life-threatening complications such as transfusion-related acute lung injury, major hemolysis, or lethal infection.
- Erythropoietin and oxygen-carrying blood substitutes remain unproven for critically ill patients.
- Massively transfused patients are at risk for hypothermia and dilutional coagulopathy.
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Red blood cells are the most efficient vehicle by which oxygen is delivered to the tissues of whole organisms. The evolution of red cells and the circulatory system allowed for the development of larger, more complex organisms with higher levels of activity. Deficiency in the number and in the local delivery of red blood cells causes relative oxygen deficiency in tissues. Oxygen deficit causes metabolic insufficiency, with inadequate energy production to sustain activity, or even life. Hemoglobin, the complex molecule contained within human red blood cells, has unique properties in and of itself, allowing for the efficient uptake of oxygen in an oxygen-rich environment, and the efficient divestiture of oxygen in an oxygen-poor environment. The whole organism also has evolved to attempt to regularly recycle and reuse the important portions of the hemoglobin molecule, thus reducing the need for ongoing sources of iron. Anemia, the lack of red blood cells in normal volumes, is therefore a disorder that threatens the homeostasis of the entire organism, and when it occurs in the setting of already life-threatening illness, anemia is a potential contributor to mortality.
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Blood transfusion has long been recognized as a potential remedy for blood loss, although the first efforts to transfuse blood from animals to human beings or from one human to another were marred by the lack of knowledge of the unique antigens on the surface of red blood cells and the immune response to them. Once a systematic approach to the collection, storage, cross-matching, and transfusion of blood was developed, enthusiasm for transfusion reached its peak. Tempered by the recognition of new transmissible illnesses, by the increasing limitations of the blood supply,1 and by the awareness of the limitations of aggressive transfusion, modern critical care practice has evolved to a more conservative approach to the use of transfusion as a remedy for anemia in critically ill patients.
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The frequency of anemia in critically ill patients has been studied in a variety of settings, all with the conclusion that it is a ...