Context Use of automated external defibrillators (AEDs) by first arriving emergency medical technicians (EMTs) is advocated to improve the outcome for out-of-hospital ventricular fibrillation (VF). However, adding AEDs to the emergency medical system in Seattle, Wash, did not improve survival. Studies in animals have shown improved outcomes when cardiopulmonary resuscitation (CPR) was administered prior to an initial shock for VF of several minutes' duration. Objective To evaluate the effects of providing 90 seconds of CPR to persons with out-of-hospital VF prior to delivery of a shock by first-arriving EMTs. Design Observational, prospectively defined, population-based study with 42 months of preintervention analysis (July 1, 1990-December 31, 1993) and 36 months of postintervention analysis (January 1, 1994-December 31, 1996). Setting Seattle fire department-based, 2-tiered emergency medical system. Participants A total of 639 patients treated for out-of-hospital VF before the intervention and 478 after the intervention. Intervention Modification of the protocol for use of AEDs, emphasizing approximately 90 seconds of CPR prior to delivery of a shock. Main Outcome Measures Survival and neurologic status at hospital discharge determined by retrospective chart review as a function of early (<4 minutes) and later (greater than or equal to 4 minutes) response intervals. Results Survival improved from 24% (155/639) to 30% (142/478) (P = .04). That benefit was predominantly in patients for whom the initial response interval was 4 minutes or longer (survival, 17% [56/321] before vs 27% [60/220] after; P = .01). In a multivariate logistic model, adjusting for differences in patient and resuscitation factors between the periods, the protocol intervention was estimated to improve survival significantly (adds ratio, 1.42; 95% confidence interval, 1.07-1.90; P = .02). Overall, the proportion of victims who survived with favorable neurologic recovery increased from 17% (106/634) to 23% (109/474) (P = .01). Among survivors, the proportion having favorable neurologic function at hospital discharge increased from 71% (106/150) to 79% (109/138) (P<.11). Conclusion The routine provision of approximately 90 seconds of CPR prior to use of AED was associated with increased survival when response intervals were 4 minutes or longer.
