Background/aim: This study aimed to evaluate the usefulness of blood gas and end-tidal carbon dioxide (EtCO2) measurements for predicting return of spontaneous circulation (ROSC) and for evaluating post-ROSC neurological survival.Materials and methods: This was a prospective case control study utilizing Atatürk University's database of adult nontraumatic patients (over 18 years old) with out-of-hospital cardiac arrest (OHCA) over the course of a year. The neurological status of the patients was evaluated after 1 h at ROSC and at hospital discharge, as defined by the cerebral performance category score. The blood gas parameters pH, PO2, PCO2, lactate, and BE were compared with EtCO2 from capnography and arteriol/alveolar carbon dioxide difference (AaDCO2) by using both blood gas and capnography upon admission to the emergency department and at ROSC.Results: A total of 155 patients were included in the study to form the control group with ROSC. The PO2, PCO2, and AaDCO2 values showed a prognostic marker for the supply of ROSC (P 0.05). Conversely, AaDCO2 was found to be significant in ROSC estimation (P 0.05).Conclusion: Blood gas parameters and EtCO2 are sufficient in predicting ROSC. The value of AaDCO2 calculated using EtCO2 and PO2may be used in predicting the prognosis of OHCA patients, but this value does not provide any conclusions concerning neurological survival.