Current status of transfusion triggers for red blood cell concentrates.

Clinical practice guidelines on red blood cell transfusion (RBC) are based on expert opinion, animal studies and the few human trials available. Twelve randomized controlled trials on the benefits of RBC transfusions in humans have been published. In the absence of definitive outcome studies, numerous theoretical arguments have been put forward in favor or against the classic transfusion threshold of 100 g/l. However, data from randomized controlled trials suggest that overall morbidity (including cardiac) and mortality, hemodynamic, pulmonary and oxygen transport variables are not different between restrictive (transfusion threshold between 70 and 80 g/l) and liberal transfusion strategies and that a restrictive transfusion strategy is not associated with increased adverse outcomes. In fact, a restrictive strategy may be associated with decreased adverse outcomes in younger and less sick critical care patients. The majority of existing guidelines conclude that transfusion is rarely indicated when the hemoglobin concentration is greater than 100 g/l and is almost always indicated when it falls below a threshold of 60 g/l in healthy, stable patients or more in older, sicker patients. In anesthetized patients, this threshold should be modulated by factors related to the dynamic nature of surgery such as uncontrolled hemorrhage, microvascular bleeding, etc. Another important role of RBC relates to primary hemostasis and higher triggers may be appropriate in coagulopathic patients. RBC concentrates are administered to correct inadequate oxygen delivery and/or to sustain primary hemostasis. Reliable monitors of tissue oxygenation and hemostasis will be required to study the benefits (or lack thereof) of RBC transfusions. The quest for a universal transfusion trigger, i.e., one that would be applicable to patients of all ages under all circumstances, must be abandoned. All RBC transfusions must be tailored to the patient's needs, at the moment the need arises. In conclusion published recommendations are commensurate with existing knowledge and, unfortunately, their conclusions are limited. Future research and development should focus on the determination of optimal transfusion strategies in various patient populations and on reliable monitors to guide transfusion therapy.