Abstract Body: Background:
Timely intervention is critical in out-of-hospital cardiac arrest (OHCA), but the influence of EMS time intervals may vary by etiology. This study examines how scene time, defined as the interval from EMS dispatch notification to arrival on scene, and total call time impact return of spontaneous circulation (ROSC) across multiple OHCA etiologies—including trauma, cardiac, overdose, drowning, asphyxia, electrocution, and exsanguination—in order to inform etiology-specific EMS strategies.

Methods:
We analyzed 225,693 OHCA cases from the 2023 National EMS Information System (NEMSIS) using multivariable logistic regression. Predictors included scene time, total EMS call time, and their interaction with arrest etiology. Time intervals were grouped into both 5- and 20-minute bins to reflect operational and clinical benchmarks. Odds ratios (OR) and 95% confidence intervals (CI) assessed associations with ROSC.

Results:
In trauma-related OHCA, scene time was significantly associated with reduced odds of ROSC (OR 0.21, 95% CI: 0.18–0.24, p < 0.001), indicating a 79% decline in survival per time bin, while total call time was not significant. For cardiac arrests, neither scene time nor call time showed a significant association with ROSC, possibly due to early interventions such as CPR or defibrillation. In overdose cases, scene time showed a non-significant trend toward improved ROSC (OR 1.64, 95% CI: 0.92–2.14, p = 0.308), suggesting benefit from extended on-scene care. ROSC remained low across all intervals for exsanguination, indicating poor prognosis. For other etiologies—drowning, asphyxia, and electrocution—no consistent time-ROSC patterns emerged, though electrocution had relatively high ROSC rates, likely due to rapid reversibility. Overall, scene time had more variable effects across etiologies than total call time. In the full model, only trauma showed a strong association between longer scene time and reduced ROSC odds.

Conclusion:
Trauma-related OHCA demonstrates significant time sensitivity, with prolonged scene time markedly reducing ROSC odds. Cardiac and overdose-related arrests exhibited less dependence on scene time, highlighting the need for tailored EMS strategies. These findings support rapid transport in trauma and suggest that extended on-scene care may be beneficial in overdose cases. This study lays the groundwork for etiology-specific EMS triage and resuscitation protocols and warrants prospective validation in future research.