Purpose: Previous observational studies have inconsistently associated early hyperoxia with worse outcomes after cardiac arrest, and have methodological limitations. We tested this association using a high-resolution database controlling for multiple disease-specific markers of severity of illness and care processes.
Methods: This was a retrospective analysis of a single-center, prospective registry of consecutive cardiac arrest patients. We included patients who survived and were mechanically ventilated ≥24 h after arrest. Our main exposure was arterial oxygen tension (PaO2), which we categorized hourly for 24 h as severe hyperoxia (>300 mmHg), moderate or probable hyperoxia (101-299 mmHg), normoxia (60-100 mmHg) or hypoxia (<60 mmHg). We controlled for Utstein-style covariates, markers of disease severity and markers of care responsiveness. We performed unadjusted and multiple logistic regression to test the association between oxygen exposure and survival to discharge, and used ordered logistic regression to test the association of oxygen exposure with neurological outcome and Sequential Organ Failure Assessment (SOFA) score at 24 h.
Results: Of 184 patients, 36 % were exposed to severe hyperoxia and overall mortality was 54 %. Severe hyperoxia, but not moderate or probable hyperoxia, was associated with decreased survival in both unadjusted and adjusted analysis [adjusted odds ratio (OR) for survival 0.83 per hour exposure, P = 0.04]. Moderate or probable hyperoxia was not associated with survival but was associated with improved SOFA score 24 h (OR 0.92, P < 0.01).
Conclusion: Severe hyperoxia was independently associated with decreased survival to hospital discharge. Moderate or probable hyperoxia was not associated with decreased survival and was associated with improved organ function at 24 h.