Blood Transfusion — When Is More Really Less?

Abstract

Blood transfusion has for years been considered to have obvious clinical benefits and to be a relatively low-risk procedure. Not until the early 1980s did transfusion practices begin to come under systematic scrutiny. Initially, this trend was driven by concern about transfusion-related infection, particularly by human immunodeficiency virus, but advances in transfusion medicine have greatly decreased the risk of transmission of viruses by transfused blood. Now, other concerns-the effects of transfusion on the immune system, transfusion related acute lung injury, and the age of transfused blood-drive the debate over transfusion practice and have led to methodical examinations of the benefits of transfusion. These new considerations are particularly important for critically ill patients. Anemia is prevalent in critically ill adults, who as a group receive a large number of red-cell transfusions. 1,2 By the third day in the intensive care unit (ICU), 95% of critically ill patients have anemia , and 40 to 50% of them will receive on average almost 5 units of red cells during their stay in the ICU. Despite the frequency of transfusion among the critically ill, the optimal treatment of anemia in euvolemic, critically ill patients remains controversial. Red-cell transfusion is commonly used in the critical care setting to increase oxygen delivery to tissues, especially in patients in shock. 3 However, several studies have raised questions regarding the validity of the assumption that red-cell transfusion is beneficial for critically ill patients with anemia. 1-4 Two plausible hypotheses could explain the apparent lack of benefit from such transfusions: immunomodulation 5 and the "storage lesion," 6 which consists of biochemical and molecular changes and an accumulation of inflammatory mediators that develop over time in stored red cells. The best evidence concerning the efficacy of red-cell transfusion in critically ill patients is from the Transfusion Requirements in Critical Care (TRICC) trial. 4 In this randomized, controlled study involving adults in critical care, a liberal transfusion strategy (target hemoglobin level, 10.0 to 12.0 g per deciliter, with a transfusion trigger of 10.0 g per deciliter) was compared with a restrictive transfusion strategy (target hemoglobin level, 7.0 to 9.0 g per deciliter, with a transfusion trigger of 7.0 g per deciliter) in a general medical and surgical setting. The restrictive group received 54% fewer red-cell units than did the liberal group, and the restrictive strategy was found to be at least as effective as the liberal strategy with respect to mortality. In patients who were less acutely ill (with a score of <20 on the Acute Physiology and Chronic Health Evaluation [APACHE II]) or under 55 years of age, the restrictive strategy was actually superior, since it was associated with a decrease in mortality, as compared with the liberal strategy. Most of the information on red-cell transfusion in critically ill patients has come from studies in adults, but such transfusions are also frequently used in critically ill infants and children. A recent observational study found that 14% of children who were admitted to a pediatric intensive care unit (PICU) received at least one red-cell transfusion during their stay in the PICU. 7 Determinants for transfusion were similar to those that have been reported in adults (anemia, cardiac disease, severity of illness, and multiple organ dysfunc-tion), suggesting that the use of red-cell transfusion in children is similar to that in adults. e d i t o r i a l