The effects of exposure to severe hyperoxemia on neurological outcome and mortality after cardiac arrest

INTRODUCTION: Hyperoxemia during cardiac arrest (CA) may increase chances of successful resuscitation. However, episodes of severe hyperoxemia after intensive care unit admission occurs frequently (up to 60%), and these have been associated with higher mortality in CA patients. The impact of severe hyperoxemia on neurological outcome is more unclear. EVIDENCE ACQUISITION: We conducted a systematic review and meta-analysis on Pubmed and EMBASE to evaluate the effects of severe hyperoxemia according to arterial blood gas analysis on neurological outcome and mortality in patients resuscitated from CA and admitted to intensive care unit. EVIDENCE SYNTHESIS: Thirteen observational studies were included, eight of them reporting data on neurological outcome and ten on mortality. Most studies reported odds ratio adjusted for confounders. Severe hyperoxemia was associated with worse neurological outcome (OR 1.37 [95%CI 1.01,1.86], P=0.04) and higher mortality at longest follow-up (OR 1.32 [95%CI 1.11,1.57], P=0.002). Subgroup analyses according to timing of hyperoxemia showed that any hyperoxemia during the first 36 hours was associated with worse neurological outcome (OR 1.52 [95%CI 1.12,2.08], P=0.008) and higher mortality (OR 1.40 [95%CI 1.18,1.66], P=0.0001), whilst early hyperoxemia was not (neurological: P=0.29; mortality: P=0.19). Sensitivity analyses mostly confirmed the results of the primary analyses. CONCLUSIONS: Severe hyperoxemia is associated with worse neurological outcome and lower survival in CA survivors admitted to intensive care unit. Clinical efforts should be made to avoid severe hyperoxemia during at least the first 36 hours after cardiac arrest.