Survival prediction of initial blood pH for nontraumatic out-of-hospital cardiac arrest patients in the emergency department

Background: Most nontraumatic out-of-hospital cardiac arrest (NTOHCA) patients who fail in prehospital resuscitation receive continued cardiopulmonary resuscitation in the emergency department (ED). Initial blood pH, which can be assessed rapidly in the ED, was examined to see whether it is a strong survival predictor for these patients. Methods: A 1-year retrospective study included consecutive 225 NTOHCA patients at a medical center in northern Taiwan who presented through the emergency medical services system. On arrival at the ED, these patients received continued cardiopulmonary resuscitation, and their initial blood pH data were assessed. Results: The pH value was positively correlated with variables such as return of spontaneous circulation, witnessed arrest, short prehospital time (≤20 minutes), and survival. The best cut-off value of initial blood pH, revealed by the receiver operating characteristic curve, was 7.068. The lowest pH value of the survivors was 6.856. The results of logistic regression model analysis shows that the odds ratios of survival was 10.0 (95% confidence interval [CI], 2.1-47.7) for patients with initial blood pH ≥ 7.068, 5.3 (95% CI, 1.48-18.9) for those with nonasystole rhythm, 4.0 (95% CI, 1.1-14.8) for those with prehospital time ≤20 minutes, and 9.1 (95% CI, 2.3-35.2) for those without NaHCO₃ administration during resuscitation, respectively. Conclusion: A cut-off value of an initial blood pH of 7.068 can serve as a predictor for survival among NTOHCA patients. In addition, patients whose initial blood pH is lower than 6.85 in the ED may not survive until hospital discharge.