Transfusion triggers.

The decision to transfuse a patient is not always clear and straightforward, particularly because no single number, neither extraction ratio nor hemoglobin level, can serve as an absolute indicator of transfusion need. Clinical assessment of the patient in conjunction with physiologic values helps in determining the appropriateness of transfusion before the advent of hypoxia or ischemia. The benefit of transfusion in relation to mortality and morbidity is discussed here based on an assessment of the literature, and transfusion guidelines from several organizations are summarized.