Arterial hyperoxia and in-hospital mortality after resuscitation from cardiac arrest

Abstract

Introduction: Hyperoxia has recently been reported as an independent risk factor for mortality in patients resuscitated from cardiac arrest. We examined the independent relationship between hyperoxia and outcomes in such patients.Methods: We divided patients resuscitated from nontraumatic cardiac arrest from 125 intensive care units (ICUs) into three groups according to worst PaO2level or alveolar-arterial O2gradient in the first 24 hours after admission. We defined 'hyperoxia' as PaO2of 300 mmHg or greater, 'hypoxia/poor O2transfer' as either PaO2< 60 mmHg or ratio of PaO2to fraction of inspired oxygen (FiO2) < 300, 'normoxia' as any value between hypoxia and hyperoxia and 'isolated hypoxemia' as PaO2< 60 mmHg regardless of FiO2. Mortality at hospital discharge was the main outcome measure.Results: Of 12,108 total patients, 1,285 (10.6%) had hyperoxia, 8,904 (73.5%) had hypoxia/poor O2transfer, 1,919 (15.9%) had normoxia and 1,168 (9.7%) had isolated hypoxemia (PaO2< 60 mmHg). The hyperoxia group had higher mortality (754 (59%) of 1,285 patients; 95% confidence interval (95% CI), 56% to 61%) than the normoxia group (911 (47%) of 1,919 patients; 95% CI, 45% to 50%) with a proportional difference of 11% (95% CI, 8% to 15%), but not higher than the hypoxia group (5,303 (60%) of 8,904 patients; 95% CI, 59% to 61%). In a multivariable model controlling for some potential confounders, including illness severity, hyperoxia had an odds ratio for hospital death of 1.2 (95% CI, 1.1 to 1.6). However, once we applied Cox proportional hazards modelling of survival, sensitivity analyses using deciles of hypoxemia, time period matching and hyperoxia defined as PaO2 > 400 mmHg, hyperoxia had no independent association with mortality. Importantly, after adjustment for FiO2and the relevant covariates, PaO2was no longer predictive of hospital mortality (P = 0.21).Conclusions: Among patients admitted to the ICU after cardiac arrest, hyperoxia did not have a robust or consistently reproducible association with mortality. We urge caution in implementing policies of deliberate decreases in FiO2in these patients. © 2011 Bellomo et al.; licensee BioMed Central Ltd.