Abstract Body (Do not enter title and authors here): Background: In out-of-hospital cardiac arrest (OHCA) patients with an initial shockable rhythm, epinephrine increases the likelihood of return of spontaneous circulation (ROSC), but its effect on neurological outcome remains uncertain. Epinephrine administered before extracorporeal resuscitation (ECPR), which is a non-pharmacological method to obtain ROSC, may have worsened neurological outcome.

Aim: To evaluate the impact of prehospital epinephrine administration on the prognosis of OHCA patients undergoing ECPR.

Methods: This is a retrospective analysis of a cohort study from a multicenter, prospective registry of 81234 OHCA patients between 2014 and 2021. After the application of exclusion criteria, 1061 OHCA patients with an initial shockable rhythm and who underwent ECPR were eligible for this study. The primary outcome was favorable neurological outcome at 30 days after the OHCA and the secondary outcome was ROSC during transfer. Patients who did and did not receive prehospital epinephrine were propensity score-matched on the basis of age, gender, witness arrest, bystander-initiated CPR, dispatcher-assisted CPR, advanced airway management, call-to-defibrillation interval, year and district.

Results: Among 1061 eligible patients, 442 patients received epinephrine and 619 patients did not. Matching was successful in achieving covariate balance as shown by a standardized difference of <10% for all variables (329 matched pairs). The proportion of patients with prehospital ROSC was significantly higher in those who received prehospital epinephrine than those who did not (36 [8%] vs 31 [5%]; adjusted odds ratio [OR] after propensity score-matching, 1.96 [95% CI 1.05-3.67], p=0.03). The proportion of patients with favorable neurological outcome at 30 days was not significantly lower in those who received prehospital epinephrine than those who did not (34 [8%] vs 78 [13%]; adjusted OR after propensity score-matching, 0.78 [95% CI 0.45-1.37], p=0.39).

Conclusion: In patients with shockable OHCA and ECPR, prehospital epinephrine administration was significantly associated with increased ROSC before hospital arrival and not significantly with decreased favorable neurological outcome at 30 days.