An oxygen balancing act: a narrative review of red blood cell transfusion in extracorporeal membrane oxygenation

Objective: To review current literature regarding red blood cell (RBC) transfusion thresholds in extracorporeal membrane oxygenation (ECMO). Background: The use of veno-venous and veno-arterial (VA) ECMO as a bridge to cardiopulmonary recovery or organ transplantation has increased in the last decade. Bleeding complications are seen in 30- 60% of patients receiving extracorporeal support. Transfusion of blood products while on ECMO occurs frequently for maintenance of the normal hemostatic balance in the setting of bleeding and coagulopathy. RBC transfusion may be indicated in patients for circuit priming, optimizing oxygen carrying capacity, and/or counteracting the effects of bleeding in the setting of anticoagulation and hemolysis due to the circuit. The current Extracorporeal Life Support Organization (ELSO) recommendation is to maintain a hematocrit of >40%. Many centers opt not to utilize a predefined trigger for transfusion and instead, tailor the thresholds based on a patient's clinical status. This is largely due to conflicting retrospective studies within the ECMO population, and the fact that recommendations are extrapolated from studies in the critical care literature, as there are no randomized controlled clinical trials for RBC transfusion thresholds in ECMO. In addition, the potential adverse effects of blood transfusions such as acute kidney injury (AKI), electrolyte imbalances, hypervolemia, and transfusion related lung injury, may outweigh the benefits. Methods: This review evaluated case/brief reports, observation studies, cohort studies, prospective trials, retrospective trials, clinical notes, expert panel reports, review articles, guidelines from international societies, and multiple original articles and references in order to determine if a standard transfusion threshold may be recommended. Conclusions: While ECMO utilization continues to expand worldwide, to date, no prospective studies have investigated the hemoglobin threshold in this population. Therefore, future large multicenter trials are essential to determine optimal monitoring, transfusion goal strategies, and guide future management.