Anemia and transfusion after aneurysmal subarachnoid hemorrhage.

Anemia is common in patients with aneurysmal subarachnoid hemorrhage (SAH), but these patients have constituted only a small fraction of those studied in large trials of anemia and transfusion. Unlike other critically ill patients, those with SAH face a well-defined risk of vasospasm and cerebral ischemia in the weeks after their hemorrhage. The risk of ongoing ischemia may make them less able to tolerate anemia and more likely to benefit from blood transfusion. The available data show that anemia is associated with poor outcomes after SAH but that blood transfusion does not consistently improve physiological markers, and it may be associated with poor outcomes. Most of these data are observational in nature, although 1 recent study demonstrated the safety and feasibility of maintaining relatively high transfusion thresholds in patients with SAH. Larger, randomized trials are needed to determine at what levels of anemia patients with SAH might benefit from transfusion, the optimal timing of transfusion, and how to identify those patients who are most likely to benefit.