Prehospital Blood pH Testing and Survival in Non-Traumatic Out-of-Hospital Cardiac Arrest: Insights from a Thai EMS Unit

Abstract

Background: Point-of-care testing (POCT) for blood gas and electrolyte analysis supports the identification of reversible causes of out-of-hospital cardiac arrest (OHCA). In 2021, the Ramathibodi Emergency Operation (RAMA EMO) unit became the first emergency medical service team in Thailand to apply POCT in its prehospital resuscitation protocol. Prior to this implementation, POCT had not been used in prehospital OHCA care in Thailand, so its clinical impact was unknown. The aim of this study was to evaluate the association between initial prehospital POCT-measured pH and return of spontaneous circulation (ROSC) at emergency department (ED) admission in a Thai EMS-managed OHCA cohort. Methods: This single-center ambispective cohort study analyzed adult non-traumatic OHCA patients managed by the RAMA EMO unit. Prehospital POCT was used in all eligible OHCA cases after the initiation of advanced resuscitation. Multivariable analysis was employed to assess the association between blood pH and ROSC at ED admission. Results: A total of 148 patients were included, and ROSC at ED admission occurred in 25% of the cases. Higher prehospital pH was significantly associated with ROSC at ED admission. In ROC analysis, a pH cutoff of ≥ 7.1 demonstrated the optimal discriminative performance. In multivariable logistic regression, pH ≥ 7.1 remained independently associated with ROSC at ED admission (adjusted odds ratio 3.68, 95% CI 1.37–9.89; P = 0.010). Internal bootstrap validation confirmed the robustness of this association. Conclusion: Prehospital POCT blood gas analysis provides valuable prognostic information regarding OHCA, with a pH ≥ 7.1 serving as an independent predictor of ROSC at ED admission. Bootstrap validation supports the stability and reliability of this cutoff. The integration of POCT into EMS protocols may enhance early clinical decision-making during resuscitation. Further external validation is warranted to confirm these findings.