Abstract Body: Background:
Lower hemoglobin levels have been associated with poor outcomes in patients with out-of-hospital cardiac arrests. Pre-arrest hemoglobin (within 24 hours) and its association with outcomes and PaO2 in in-hospital cardiac arrest (IHCA) remains unknown. We aimed to evaluate the association of pre-arrest hemoglobin levels with survival and neurologic outcomes, and intra-arrest PaO2 levels in adults with IHCA.

Methods:
The study population included adults with IHCA undergoing resuscitation at an academic tertiary medical center from 2011-2019. Hemoglobin levels were obtained within 24 hours prior to arrest, and PaO2 levels were obtained intra-arrest via arterial blood gas samples. Patients were classified based upon three pre-arrest hemoglobin (Hgb) levels: Hgb < 8.5, Hgb 8.5-10.5, Hgb > 10.5. Return of spontaneous circulation (ROSC), survival to discharge, favorable neurological outcome (defined as a Glasgow Outcome Score of 4-5), and association with PaO2 served as outcomes of interest.

Results:
Of the 799 patients studied, 493 patients had pre-arrest hemoglobin data and 164 had intra-arrest PaO2 data. Of those patients that had pre-arrest hemoglobin data, 145 (29.4%) had Hgb < 8.5, 178 (36.1%) had Hgb 8.5-10.5, 170 (34.5%) had Hgb >10.5. Charlson Comorbidity Score was similar across each hemoglobin group. Most patients had PEA/Asystole as the initial rhythm at onset of cardiac arrest, and the number was similar across each hemoglobin group. Mean intra-arrest PaO2 was higher in the Hgb < 8.5 group. Compared to Hgb < 8.5, higher hemoglobin levels were associated with higher rates of ROSC in both univariate (Hgb < 8.5: 46.9% vs. Hgb 8.5-10.5: 59.6% vs. Hgb > 10.5: 62.9%, p = 0.012) and multivariate (Hgb 8.5-10.5: OR 1.51, 95% CI 0.96-2.39; Hgb > 10.5: OR 1.75, 95% CI 1.10-2.79) analyses. Higher hemoglobin levels were associated with higher rates of favorable neurologic outcome in the univariate analysis only (Hgb < 8.5: 10.5% vs. Hgb 8.5-10.5: 11.8% vs. Hgb > 10.5: 19.4%, p = 0.043). There was no significant correlation between pre-arrest hemoglobin and intra-arrest PaO2.

Conclusions:
In this contemporary registry of adults with IHCA, higher hemoglobin values were associated with higher rates of ROSC. There may be an association between higher hemoglobin levels and favorable neurologic outcome. There was no association between pre-arrest hemoglobin and intra-arrest PaO2.