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 (PaO) levels was measured during resuscitation. Main exposure was intra-arrest PaO level, which was divided into three categories: hypoxaemia, PaO < 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 PaO 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 PaO categories were associated with favourable functional survival and the adjusted odds ratios increased as the PaO 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.