Early physician intervention via rapid response vehicle preserves the predictive accuracy of the prehospital R-EDByUS score in OHCA

Background Several scoring systems (e.g., MIRACLE2, OHCA, CAHP, TTM) have been developed to predict neurological outcomes in out-of-hospital cardiac arrest (OHCA) by incorporating post-hospitalization data. In contrast, the R-EDByUS score is a prehospital-only prognostic tool that evaluates both patient-related factors (e.g., age and initial shockable rhythm) and elements of the underlying emergency system infrastructure (e.g., time to return of spontaneous circulation [ROSC] or transport, witnessed arrest, and bystander cardiopulmonary resuscitation [CPR]). Our institution’s Rapid Response Vehicle (Dr Car) system enables earlier first medical contact—effectively advancing the virtual hospital arrival time—and provides prompt physician intervention that may modify these factors. This study examines whether the predictive accuracy of the R-EDByUS score is maintained in the Dr Car setting, where early intervention is available. Methods We retrospectively analyzed 793 adult OHCA cases transported to our institution between 2015 and 2021. Patients were categorized into two cohorts based on their status at first medical contact: those achieving ROSC and those requiring ongoing CPR. The Dr Car group was compared with the standard emergency medical service (EMS) group. The primary outcome was an unfavorable neurological status (CPC 3–5) at 30 days. To assess whether the R-EDByUS score’s predictive accuracy is preserved under early intervention conditions, we performed propensity score matching using the score’s components. Results Among 306 ROSC cases (EMS: 208; Dr Car: 98), the R-EDByUS score demonstrated a C-statistic of 0.8771. Neurological outcomes were significantly better in the Dr Car group (p < 0.001), despite longer transport times. After propensity score matching, no significant difference in outcomes was observed, indicating that the R-EDByUS score remains valid even with early physician intervention. Among 487 CPR cases (EMS: 228; Dr Car: 259), the score yielded a C-statistic of 0.7818. Neurological outcomes were significantly better in the Dr Car group (p = 0.017), and after propensity score matching—even with longer transport times—the outcomes remained comparable, further supporting the reliability of the R-EDByUS score under early intervention conditions. Conclusions Early first medical contact via the Dr Car system—effectively advancing the virtual hospital arrival time—contributes to improved neurological outcomes in OHCA patients. Although the scope of care provided by Dr Car is limited compared to full in-hospital treatment, this early intervention yields outcomes comparable to those achieved by standard EMS care. The maintained predictive accuracy of the R-EDByUS score underscores its value in guiding prehospital decision-making across diverse emergency response models. Further studies are warranted to refine Dr Car dispatch protocols and assess its cost-effectiveness in clinical practice.