Red blood cell transfusion in the intensive care setting: controversies amongst evidence.

Anemia is a prevalent issue in intensive care units. It appears in the first days, and may continue or worsen during hospital stay. Its etiology is generally multifactorial. Red blood cell transfusion is the most common intervention for treating anemia. Approximately 12 million blood units are used for transfusions in the United States, 25% to 30% in the intensive care units. Due to reduction of transfusion infections the increased safety has allowed an expansion of clinical indications. However, transfusion therapy is associated with other adverse effects such as nosocomial infections, immunological impairment, lung injury, hemolytic reactions and higher cancer incidence. Various papers have tried to show an association between correction of anemia and mortality-morbidity, but no consensus has been reached in literature. One of the current World Health Organization's proposals is to reduce potentially unnecessary transfusions, promoting a rational transfusion attitude. The primary objective of this narrative review is to approach controversies regarding the transfusion threshold according to recent studies, and as a secondary objective, it aims to discuss iatrogenic anemia aspects and the different behaviors among intensivists on the best practices for implementation of transfusion practices. It is not within our objectives to discuss transfusion complications, although they are mentioned. A search was conducted on electronic literature databases (PubMed - Clinical Queries), and UpToDate 16.2, and additional consultation to textbooks. It became clear that transfusion practices are widely variable among intensive care units. Evidence is scarce that routine transfusion in non-hemorrhagic patients should be used in those with > 7 g/dL hemoglobin. There is no consensus on the transfusion threshold in critically ill patients. Cardiovascular disease patients seem to present a higher risk of death than non-cardiovascular patients, for any level of hemoglobin. Transfusion guided by hemoglobin levels and individual oxy-hemodynamic physiologic parameters and clinical context is apparently, the current best accepted strategy, rather than arbitrary and isolated hemoglobin correction.