Association of blood carboxyhemoglobin levels with mortality and neurological outcomes in out-of-hospital cardiac arrest

Background: Carbon monoxide (CO), produced endogenously by heme oxygenase-1, plays a crucial role in the immune system by mitigating cellular damage under stress. However, the significance of carboxyhemoglobin (COHb) levels after out-of-hospital cardiac arrest (OHCA) is not well understood. This study aimed to explore the association between COHb levels at hospital arrival and within the first 24 h post-arrival with 30-day mortality and neurological outcomes in patients who experienced OHCA.
Methods: This single-center, retrospective study analyzed data from adult patients who experienced OHCA seen at Okayama University Hospital from 2019 to 2023. The patients were assigned to one of two study groups based on COHb levels (0.0% or >= 0.1%) upon hospital arrival. The primary outcome was 30-day mortality.
Results: Among the 560 eligible patients who experienced OHCA, 284 (50.7%) were in the COHb 0.0% group and 276 (49.3%) were in the COHb >= 0.1% group. The 30-day mortality was significantly higher in the COHb 0.0% group compared to the COHb >= 0.1% group (264 [92.9%] vs. 233 [84.4%]). Multivariable logistic regression showed that the COHb 0.0% group was associated with 30-day mortality (adjusted ORs: 2.24, 95% CIs: 1.10-4.56). Non-survivors at 30 days who were admitted to the intensive care unit had lower COHb levels at hospital arrival (0.0% vs. 0.2%) and lower mean COHb levels during the first 24 h post-arrival (0.7% vs. 0.9%) compared to survivors.
Conclusions: COHb levels of 0.0% were linked to worse outcomes in patients experiencing OHCA, warranting further research on the prognostic implications of COHb in this context.