Abstract
IntroductionPost-cardiac arrest patients are often exposed to 100% oxygen during cardiopulmonary resuscitation and the early post-arrest period. It is unclear whether this contributes to development of pulmonary dysfunction or other patient outcomes.MethodsWe performed a retrospective cohort study including post-arrest patients who survived and were mechanically ventilated at least 24 hours after return of spontaneous circulation. Our primary exposure of interest was inspired oxygen, which we operationalized by calculating the area under the curve of the fraction of inspired oxygen (FiO2AUC) for each patient over 24 hours. We collected baseline demographic, cardiovascular, pulmonary and cardiac arrest-specific covariates. Our main outcomes were change in the respiratory subscale of the Sequential Organ Failure Assessment score (SOFA-R) and change in dynamic pulmonary compliance from baseline to 48 hours. Secondary outcomes were survival to hospital discharge and Cerebral Performance Category at discharge.ResultsWe included 170 patients. The first partial pressure of arterial oxygen (PaO2):FiO2 ratio was 241 ± 137, and 85% of patients had pulmonary failure and 55% had cardiovascular failure at presentation. Higher FiO2AUC was not associated with change in SOFA-R score or dynamic pulmonary compliance from baseline to 48 hours. However, higher FiO2AUC was associated with decreased survival to hospital discharge and worse neurological outcomes. This was driven by a 50% decrease in survival in the highest quartile of FiO2AUC compared to other quartiles (odds ratio for survival in the highest quartile compared to the lowest three quartiles 0.32 (95% confidence interval 0.13 to 0.79), P = 0.003).ConclusionsHigher exposure to inhaled oxygen in the first 24 hours after cardiac arrest was not associated with deterioration in gas exchange or pulmonary compliance after cardiac arrest, but was associated with decreased survival and worse neurological outcomes.Electronic supplementary materialThe online version of this article (doi:10.1186/s13054-015-0824-x) contains supplementary material, which is available to authorized users.
Highlights
Post-cardiac arrest patients are often exposed to 100% oxygen during cardiopulmonary resuscitation and the early post-arrest period
We excluded patients if the time of return of spontaneous circulation (ROSC) was unknown, if vital signs and vasopressor requirements were not recorded within 6 h of ROSC, or if arterial blood gas (ABG) or ventilator data were not recorded within 4 h of ROSC (we have previously reported that this is the timeframe during which patients are most often exposed to high fraction of inspired oxygen (FiO2) levels [10])
When partial pressure of arterial oxygen (PaO2) data were unavailable even within 12 h of a given time point (3.2% of cases), we calculated sequential organ failure assessment (SOFA)-R using peripheral oxygen saturation (SpO2) which is recorded hourly based on the following table, which we developed on the basis of a previously validated SpO2:FiO2 estimation for P:F ratio [28]
Summary
Post-cardiac arrest patients are often exposed to 100% oxygen during cardiopulmonary resuscitation and the early post-arrest period. Observational studies have associated higher arterial oxygen concentration (hyperoxia) with worsened clinical outcomes [7,8,9,10]. Authors of these studies have hypothesized that this effect is mediated through worsening of secondary brain injury by increased oxidative stress and free radical formation, but other possible explanations for this association have not been previously. Early clinical reports of pulmonary oxygen toxicity were conducted when open-lung ventilation with high tidal volumes was standard practice [20,21,22]
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