Time from Cardiopulmonary Resuscitation Initiation to Prehospital Return of Spontaneous Circulation and Downstream Outcomes Among Adult Out-of-Hospital Cardiac Arrest Patients Achieving Field ROSC: A 2015–2023 Smart Advanced Life Support Registry Stu

Background: Prehospital return of spontaneous circulation (ROSC) is a widely used intermediate endpoint in out-of-hospital cardiac arrest (OHCA), but its downstream clinical meaning may differ according to when ROSC is achieved. Methods: We conducted a retrospective registry-based cohort study of adult non-traumatic OHCA patients treated with Smart Advanced Life Support (SALS) from 2015 to 2023 who achieved prehospital ROSC. The primary exposure was the low-flow interval, defined as the interval from CPR initiation to first prehospital ROSC, categorized a priori as <10, 10–14, 15–19, 20–24, 25–29, and ≥30 min. Multivariable logistic regression models estimated associations with good neurological recovery, prehospital rearrest, survival to hospital admission, and survival to discharge, adjusting for age, sex, witnessed arrest, bystander CPR, initial shockable rhythm, transport time interval, and region. Results: Among 19,156 adult SALS-treated OHCA patients, 4195 achieved prehospital ROSC; 3760 had valid low-flow interval values from 0 to 60 min and were included in the primary analysis. Good neurological recovery decreased from 582/1004 (58.0%) in the <10 min group to 17/249 (6.8%) in the ≥30 min group, while prehospital rearrest increased from 194/488 (39.8%) to 136/174 (78.2%). Compared with <10 min, the adjusted odds ratios for good neurological recovery were 0.368, 0.164, 0.135, 0.099, and 0.081 across progressively later ROSC categories. The adjusted odds ratio for rearrest in the ≥30 min group was 5.024. Conclusions: In this selected SALS-treated ROSC-positive OHCA cohort, later low-flow interval was associated with substantially lower odds of favorable neurological recovery and survival and higher odds of prehospital rearrest. These findings suggest that prehospital ROSC timing may serve as a prognostic marker but should not be interpreted as a standalone criterion for treatment termination or transport decisions.