INTRODUCTION: For out-of-hospital cardiac arrest (OHCA) with refractory arrest, transport to hospital with ongoing cardiopulmonary resuscitation (CPR)-"intra-arrest transport (IAT)"-is a treatment option, however it may reduce resuscitation quality. Unfortunately, international registries do not measure IAT directly, but other variables may be used to estimate IAT. We compared three indirect definitions to a direct measurement of IAT. METHODS: We included advanced life support-treated adult non-traumatic OHCA from a large metropolitan emergency medical services network (2021-2023). We reviewed prehospital records and cardiac monitor files to identify IAT, defined as CPR in progress at time of transport. We compared this to three indirect definitions, including transport prior to: (1) "Any ROSC"
(2)"Sustained ROSC" (≥20 min or present at ED)
or, (3) "Post-ROSC Vitals" (1st blood pressure/12-lead ECG.) RESULTS: Of 1,269 cases, the median age was 71 years (IQR: 60-81), 523 (41%) were female, 128 (10%) had initial shockable rhythms, 336 (26%) achieved ROSC on scene and were transported (75 of 200 [38%] with available data experienced rearrest on scene). Overall, 472 (37%, 95% CI: 34-40%) received IAT (direct definition). Indirect definitions of "Any ROSC", "Sustained ROSC", and "Post-ROSC Vitals" demonstrated sensitivity and specificities of 78.0%/100.0%, 98.5%/97.0%, and 82.4%/97.6%, respectively. CONCLUSION: Compared to a direct measurement of IAT, the indirect definition using "Any ROSC" demonstrated the lowest sensitivity
however, the definition using "Sustained ROSC" showed the highest sensitivity and specificity. These indirect definitions may support estimation of IAT within future research and quality initiatives.