Low hemoglobin levels are associated with lower cerebral saturations and poor outcome after cardiac arrest

PurposePost-cardiac arrest (CA) patients have a large cerebral penumbra at risk for secondary ischemic damage in case of suboptimal brain oxygenation during ICU stay. The aims of this study were to investigate the association between hemoglobin, cerebral oxygenation (SctO2) and outcome in post-CA patients.MethodsProspective observational study in 82 post-CA patients. Hemoglobin, a corresponding SctO2 measured by NIRS and SVO2 in patients with a pulmonary artery catheter (n = 62) were determined hourly during hypothermia in the first 24 h of ICU stay.ResultsWe found a strong linear relationship between hemoglobin and mean SctO2 (SctO2 = 0.70 × hemoglobin + 56 (R2 0.84, p = 10−6)). Hemoglobin levels below 10 g/dl generally resulted in lower brain oxygenation. There was a significant association between good neurological outcome (43/82 patients in CPC 1-2 at 180 days post-CA) and admission hemoglobin above 13 g/dl (OR 2.76, 95% CI 1.09:7.00, p = 0.03) or mean hemoglobin above 12.3 g/dl (OR 2.88, 95%CI 1.02:8.16, p = 0.04). This association was entirely driven by results obtained in patients with a mean SVO2 below 70% (OR 6.25, 95%CI 1.33:29.43, p = 0.01) and a mean SctO2 below 62.5% (OR 5.87, 95%CI 1.08:32.00, p = 0.03).ConclusionHemoglobin levels below 10 g/dl generally resulted in lower cerebral oxygenation. Average hemoglobin levels below 12.3 g/dl were associated with worse outcome in patients with suboptimal SVO2 or SctO2. The safety of a universal restrictive transfusion threshold of 7 g/dl can be questioned in post-CA patients.