Effects of red blood cell transfusion on global oxygenation in anemic critically ill patients

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)vO₂ , lactate level, venous-to-arterial carbon dioxide difference (Pv-aCO₂ ), and cardiac index/EO₂ (CI/EO₂ ) and evaluated their usefulness in guiding transfusion decisions in ICU patients.

Prospectively, all adult patients transfused were included except those with active bleeding or without a jugular or subclavian catheter. We measured O₂ parameters before and after transfusion. Patients were a priori grouped according to their initial S(c)vO₂ (< or ≥70%), treatment with vasopressors, cardiac function, and septic status.

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)vO₂ (65% [59%-73%] to 69% [62%-75%]) increased after transfusion (all P < .001). S(c)vO₂ improved after transfusion only when initial S(c)vO₂ was less than 70% (62% [56%-65%] to 66% [61%-71%]; P < .001). In this group, Pv-aCO₂ , lactate concentrations, and CI/EO₂ did not change after transfusion. Cardiac function, sepsis, or vasopressor therapy did not affect these results.

Among systemic O₂ parameters, only a S(c)vO₂ < 70% in anemic ICU patients improves after transfusion. As S(c)vO₂ 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.