Effects of Red Blood Cell Transfusion on Global Oxygenation in Anemic Critically Ill Patients

Background Consensus for transfusion in intensive care unit (ICU) patients recommends a restrictive strategy, based on a hemoglobin (Hb) concentration of 7 g/dL. Red blood cell (RBC) transfusion is used to prevent tissue hypoxia by improving oxygen transport (DO2) and therefore oxygen consumption (VO2). We studied the effects of RBC transfusion on systemic oxygenation parameters reflecting systemic oxygen extraction (EO2 = DO2/VO2): S(c)vO(2), lactate level, venous-to-arterial carbon dioxide difference (Pv-aCO(2)), and cardiac index/EO2 (CI/EO2) and evaluated their usefulness in guiding transfusion decisions in ICU patients. Study Design and Methods Prospectively, all adult patients transfused were included except those with active bleeding or without a jugular or subclavian catheter. We measured O-2 parameters before and after transfusion. Patients were a priori grouped according to their initial S(c)vO(2) (< or >= 70%), treatment with vasopressors, cardiac function, and septic status. Results A total of 62 patients received 105 RBC transfusions. For all, mean arterial pressure (77 [69-88] to 81 [73-91] mm Hg), Hb concentration (7.4 [7.0-7.8] to 8.4 [7.7-8.9] g/dL) and S(c)vO(2) (65% [59%-73%] to 69% [62%-75%]) increased after transfusion (all P < .001). S(c)vO(2) improved after transfusion only when initial S(c)vO(2) was less than 70% (62% [56%-65%] to 66% [61%-71%]; P < .001). In this group, Pv-aCO(2), lactate concentrations, and CI/EO2 did not change after transfusion. Cardiac function, sepsis, or vasopressor therapy did not affect these results. Conclusions Among systemic O-2 parameters, only a S(c)vO(2) < 70% in anemic ICU patients improves after transfusion. As S(c)vO(2) can reflect a DO2/VO2 imbalance, it could be helpful when combined with the Hb concentration to decide whether to transfuse. However, the benefit on outcome should be further studied.