Impact of number of defibrillation attempts on neurologically favourable survival rate in patients with Out-of-Hospital cardiac arrest

Aim of the study: Defibrillation plays a crucial role in early return of spontaneous circulation (ROSC) and survival of patients with out-of-hospital cardiac arrest (OHCA) and shockable rhythm. Prehospital adrenaline administration increases the probability of prehospital ROSC. However, little is known about the relationship between number of prehospital defibrillation attempts and neurologically favourable survival in patients treated with and without adrenaline. Methods: Using a nationwide Japanese OHCA registry database from 2006 to 2020, 1,802,084 patients with OHCA were retrospectively analysed, among whom 81,056 with witnessed OHCA and initial shockable rhythm were included. The relationship between the number of defibrillation attempts before hospital admission and neurologically favourable survival rate (cerebral performance category score of 1 or 2) at 1 month was evaluated with subgroup analysis for patients treated with and without adrenaline. Results: At 1 month, 18,080 (22.3%) patients had a cerebral performance category score of 1 or 2. In the study population, the probability of pre-hospital ROSC and favourable neurological survival rate were inversely associated with number of defibrillation attempts. Similar trends were observed in patients treated without adrenaline, whereas a greater number of defibrillation attempts was counterintuitively associated with favourable neurological survival rate in patients treated with prehospital adrenaline. Conclusions: Overall, a greater number of prehospital defibrillation attempts was associated with lower neurologically favourable survival at 1 month in patients with OHCA and shockable rhythm. However, an increasing number of shocks (up to the 4th shock) was associated with better neurological outcomes when considering only patients treated with adrenaline.