Background The choice of a defibrillation or a cardiopulmonary resuscitation (CPR)-first strategy in the treatment of prolonged cardiac arrest (CA) is still controversial.The purpose of this study was to compare the effects of defibrillation or CPR administered first on neurological prognostic markers in a porcine model of prolonged CA.Methods After 8 minutes of untreated ventricular fibrillation (VF),24 inbred Chinese Wuzhishan minipigs were randomized to receive either defibrillation first (ID group,n=12) or chest compression first (IC group,n=12).In the ID group,a shock was delivered immediately.If defibrillation failed to attain restoration of spontaneous circulation (ROSC),manual chest compressions were rapidly initiated at a rate of 100 compressions/min and a compression-to-ventilation ratio of 30:2.If VF persisted after five cycles of CPR,a second defibrillation attempt was made.In the IC group,chest compressions were delivered first,followed by a shock.After successful ROSC,hemodynamic status and blood samples were obtained at 0.5,1,2,4,6,and 24 hours after ROSC.Porcine-specific neuron-specific enolase (NSE) and S100B were measured from sera using enzyme-linked immunosorbent assays.Porcine cerebral performance category scores were used to evaluate preliminary neurological function following 24 hours recovery.Surviving pigs were sacrificed at 24 hours after ROSC and brains were removed for electron microscopy analysis.Results The number of shocks,total defibrillation energy,and time to ROSC were significantly lower in the ID group compared with the IC group.Compared with the IC group,S100B expression was decreased at 2 and 4 hours after ROSC,and NSE expression decreased at 6 and 24 hours after ROSC in the ID group.Brain tissue analysis showed that injury was attenuated in the ID group compared with the IC group.There were no significant differences between 6 and 24 hours survival rates.Conclusion Defibrillation first may result in a shorter time to ROSC and lower biochemical markers of brain injury in a porcine model of 8-minute CA due to VF,but the choice of different resuscitation strategies did not affect the rate of ROSC and 24-hour survival.