Arterial Blood Gas Tensions After Resuscitation From Out-of-Hospital Cardiac Arrest: Associations With Long-Term Neurologic Outcome

Objectives Optimal oxygen and carbon dioxide levels during postcardiac arrest care are currently undefined and observational studies have suggested harm from hyperoxia exposure. We aimed to assess whether mean and time-weighted oxygen and carbon dioxide levels during the first 24 hours of postcardiac arrest care correlate with 12-month neurologic outcome. Design Prospective observational cohort study. Setting Twenty-one ICUs in Finland. Patients Out-of-hospital cardiac arrest patients treated in ICUs in Finland between March 2010 and February 2011. Interventions None. Measurements and Main Results: Arterial blood Pao(2) and Paco(2) during the first 24 hours from admission were divided into predefined categories from the lowest to the highest. Proportions of time spent in different categories and the mean Pao(2) and Paco(2) values during the first 24 hours were included in separate multivariable regression models along with resuscitation factors. The cerebral performance category at 12 months was used as primary endpoint. A total of 409 patients with arterial blood gases analyzed at least once and with a complete set of resuscitation data were included. The average amount of Pao(2) and Paco(2) measurements was eight per patient. The mean 24 hours Paco(2) level was an independent predictor of good outcome (odds ratio, 1.054; 95% CI, 1.006-1.104; p = 0.027) but the mean Pao(2) value was not (odds ratio, 1.006; 95% CI, 0.998-1.014; p = 0.149). With multivariate regression analysis, time spent in the Paco(2) band higher than 45 mm Hg was associated with good outcome (odds ratio, 1.015; 95% CI, 1.002-1.029; p = 0.024, for each percentage point increase in time) but time spent in different oxygen categories were not. Conclusions: In this multicenter study, hypercapnia was associated with good 12-month outcome in patients resuscitated from out-of-hospital cardiac arrest. We were unable to verify any harm from hyperoxia exposure. Further trials should focus on whether moderate hypercapnia during postcardiac arrest care improves outcome.