Outcomes associated with intra-arrest hyperoxaemia in out-of-hospital cardiac arrest: A registry-based cohort study

Background: An association between post-arrest hyperoxaemia and worse outcomes has been reported for out-of-hospital cardiac arrest (OHCA) patients, but little is known about the relationship between intra-arrest hyperoxaemia and clinically relevant outcomes. This study aimed to investigate the association between intra-arrest hyperoxaemia and outcomes for OHCA patients.

Methods: This was an observational study using a registry database of OHCA cases that occurred between 2014 and 2017 in Japan. We included adult, non-traumatic OHCA patients who were in cardiac arrest at the time of hospital arrival and for whom partial pressure of arterial oxygen (PaO₂) levels was measured during resuscitation. Main exposure was intra-arrest PaO₂ level, which was divided into three categories: hypoxaemia, PaO₂ < 60 mmHg; normoxaemia, 60-300; or hyperoxaemia, ≥300. Primary outcome was favourable functional survival at one month or at hospital discharge. Multivariable logistic regression was performed to adjust for clinically relevant variables.

Results: Among 16,013 patients who met the eligibility criteria, the proportion of favourable functional survival increased as the PaO₂ categories became higher: 0.5 % (57/11,484) in hypoxaemia, 1.1 % (48/4243) in normoxaemia, and 5.2 % (15/286) in hyperoxaemia (p-value for trend < 0.001). Higher PaO₂ categories were associated with favourable functional survival and the adjusted odds ratios increased as the PaO₂ categories became higher: 2.09 (95 % CI: 1.39-3.14) in normoxaemia and 5.04 (95 % CI: 2.62-9.70) in hyperoxaemia when compared to hypoxaemia as a reference.

Conclusion: In this observational study of adult OHCA patients, intra-arrest normoxaemia and hyperoxaemia were associated with better functional survival, compared to hypoxaemia.