Red blood cell transfusion in brain-injured patients: a paradigm shift?

Hemoglobin (Hb) is a critical component of arterial oxygen content, and thus of oxygen delivery to the brain. As a result, anemia is a major concern in patients with acute brain injury such as traumatic brain injury (TBI), aneurysmal subarachnoid hemorrhage (aSAH), or intracranial hemorrhage (ICH). In these patients, anemia has been associated with higher mortality and worse neurological outcomes. However, the safety and benefit of red blood cell (RBC) transfusion remained uncertain in observational studies. Until recently, there was limited evidence to guide the optimal transfusion threshold: whether to adopt a liberal or a restrictive RBC transfusion strategy. In 2024, three randomized controlled trials compared liberal (Hb threshold 9-10 g·dL^-1) vs. restrictive (Hb threshold 7-8 g·dL^-1) transfusion strategies in patients with aSAH (SAHARA), TBI (HEMOTION), or mixed acute brain injury (TRAIN). Of these, only TRAIN demonstrated a significant benefit for the liberal strategy (Hb 9 g·dL^-1) over the restrictive one (Hb 7 g·dL^-1) in improving 6-month neurological outcomes. HEMOTION showed a non-significant trend favoring the liberal strategy (Hb 10 g·dL^-1). When combined in meta-analyses, these findings suggest adopting a more liberal transfusion threshold (9-10 g·dL^-1) in patients with acute brain injury, especially those with TBI. Moving forward, a personalized transfusion strategy - guided by clinical context, timing, and neuromonitoring - may offer the best approach for this hypoxia-sensitive population.