Oxygen Extraction Ratios to Guide Red Blood Cell Transfusion

Hemoglobin-based red blood cell transfusion (RBC) triggers do not clearly identify which patients with moderate anemia (hemoglobin 7-10 g/dL) will benefit from RBC transfusion. The National Heart, Lung, and Blood Institute has recognized the need for bedside oxygenation measures to enhance transfusion decision-making. This narrative review uses four studies to explore the potential of the oxygen extraction ratio (O₂ER)-the ratio of consumed oxygen to delivered oxygen in a critical tissue bed as a more physiologically relevant indicator for guiding RBC transfusions in patients with moderate anemia. The aim of this review is to present existing data on the relationship between O₂ER and responsiveness to RBC transfusion, as well as the feasibility of O₂ER as bedside measure of tissue oxygenation. This review presents a narrative appraisal of three critical papers that investigate the relationship between O₂ER and transfusion outcomes, and one paper that demonstrates proof-of-concept for a noninvasive device to measure O₂ER at the bedside. Despite limitations in the existing studies, including small sample sizes and observational designs, the evidence collectively suggests that O₂ER has the potential to enhance transfusion decision accuracy. The development of noninvasive measurement devices could facilitate widespread implementation in many kinds of care settings.