Red blood cell transfusion in the critically ill patient

Red blood cell (RBC) transfusion is commonly required in critically ill patients. Several recent, observational, multicenter studies reported that approximately one third of critically ill patients received a blood transfusion at one time or another during their stay in the intensive care unit (ICU) (Table 1). Because of the frequent use of this intervention, it is important for the ICU physician to be aware of recent developments in this continuously evolving field of medicine. In this narrative review, we consider some key aspects of transfusion medicine in the ICU, focusing on aspects relevant to the critically ill patient, including prevalence and reasons for blood transfusion, epidemiology and etiology of anemia in these patients, pathophysiological considerations on tolerance to anemia, and efficacy of RBC transfusion. Safety concerns, including questions of RBC storage and leukoreduction, are then discussed, followed by a proposal for an integrated approach to transfusion decisions and a discussion on economic aspects and alternatives to blood transfusion.Anemia is common in ICU patients and appears early in the ICU course [1]. In an observational, multicenter, cohort study in Scotland, 25% of patients admitted to the ICU had a hemoglobin level < 9 g/dl [2]. Similar results were reported in the ABC study [3], in which 29% of patients had a hemoglobin concentration < 10 g/dl on admission. Even in nonbleeding ICU patients, hemoglobin levels tend to decrease early [3]. This decrease is more pronounced in septic than in nonseptic patients [4], at least in part because of their inflammatory response; more frequent blood sampling may also contribute.Interestingly, anemia and the need to restore adequate oxygen delivery (DO2) are the most common indications for transfusion, rather than acute bleeding [3,5-10]. Anemia in the critically ill patient is a multifactorial phenomenon that has been compared to the so-called "anemia of chronic illness" [11]. Apart from evide