Association between mean arterial blood gas tension and outcome in cardiac arrest patients treated with therapeutic hypothermia

Background Studies investigating the relationship between blood gas tension and outcome in cardiac arrest survivors have reported conflicting results. This might have resulted from the use of a blood gas value at a single time point and the difference in the proportion of patients treated with therapeutic hypothermia (TH). We investigated the association of the mean blood gas tensions calculated from blood gas values obtained between restoration of spontaneous circulation and end of TH with the outcome in cardiac arrest patients treated with TH. Methods This was a retrospective observational study including 213 adult cardiac arrest patients. The cohort was divided into four categories based on the distribution of the mean Pao 2 data using quartiles as cut-off values between categories. According to the mean Paco 2 , the cohort was divided into hypocarbia, normocarbia, and hypercarbia. The primary outcome was in-hospital mortality. Results In multivariate analysis, the mean Pao 2 quartile was not associated with in-hospital mortality, but hypocarbia was significantly associated with increased risk of in-hospital mortality (odds ratio 2.522; 95% confidence interval 1.184-5.372; P = .016). We found a V-shaped independent association between the mean Pao 2 and poor neurologic outcome at hospital discharge, with the risk of poor neurologic outcome increasing with a descending and ascending Pao 2 ranges. Conclusion Mean Pao 2 had no independent association with in-hospital mortality whereas hypocarbia was independently associated with in-hospital mortality. We also found a V-shaped independent association between the mean Pao 2 and poor neurologic outcome at hospital discharge.