Relationship between hemoglobin concentrations and outcomes across subgroups of patients with aneurysmal subarachnoid hemorrhage

Objective: Anemia predicts poor outcome following aneurysmal subarachnoid hemorrhage (SAH). We hypothesized that this association would be stronger among patients with more severe SAH, since these patients are likely to be more vulnerable to secondary brain injury in the form of reduced cerebral oxygen delivery. Methods: Daily nadir hemoglobin (Hb) concentrations over 2 weeks following SAH were retrieved in 245 consecutive patients, and compared between those with a favorable versus unfavorable outcome. The analysis was repeated with patients dichotomized as follows: WFNS score 4-5 vs. 1-3; modified Fisher score (MFS) 4 vs. 0-3; and vasospasm present vs. absent. Mixed effect models and multivariable analysis using the generalized estimating equation were employed to assess correlated data with repeated measures. Results: Patients with an unfavorable outcome consistently had lower Hb concentrations, especially between days 6-11 following SAH (P ranging from <0.001 to 0.009), as well as a greater fall in Hb over time (β = -0.07, P < 0.001). This was true regardless of WFNS score, MFS, or the presence or absence of vasospasm. However, the effect was somewhat more pronounced among patients with higher WFNS and modified Fisher scores. Conclusion: Lower Hb levels are associated with worse outcomes regardless of SAH severity or the development of vasospasm. This finding may imply that a lower Hb concentration is largely a marker for a greater degree of systemic illness, rather than necessarily causing direct harm. However, the association is somewhat stronger among patients with more severe SAH. Thus, if there is a benefit for maintaining higher Hb levels with transfusions or erythropoietin, it may be more pronounced among these patients.