Relationship of timeliness of paramedic advanced life support interventions to outcome in out-of-hospital cardiac arrest treated by first responders with defibrillators

Study objective: We sought to determine whether the interval between the arrival of first responder/defibrillators and paramedic advanced life support (ALS) interventions is associated with outcome. Methods: We carried out a prospective observational study of adults in out-of-hospital cardiac arrest treated by both first responders and paramedics in an urban emergency medical services system between July 15, 1992, and May 27, 1993 (N=544). Results: The gap between first-responder and medic arrival was short (3.2 minutes); medics arrived before first-responder shock in 22% of ventricular fibrillation (VF) cases. Just 10% of patients had a pulse when medics arrived, but the presence of pulse on medic arrival was a powerful predictor of hospital discharge (odds ratio [OR], 20.5; sensitivity, 39%; specificity, 98%; positive predictive value, 55%; negative predictive value, 97%) or a Cerebral Performance Category score on discharge of 1 or 2 (OR, 2.9). No response or individual ALS treatment interval was related to outcome, including the interval from first-responder to medic arrival. ALS interventions by medics were associated with poorer outcomes; even the need for nothing more than additional defibrillation by medics decreased the survival rate of VF patients threefold. By contrast, bystander CPR improved survival more than fourfold and early defibrillation of VF by first responders more than ninefold. Ninety-one percent of all patients discharged from the hospital who received only minimal ALS other than intubation had good neurologic outcome and longer survival after discharge. Half the total survivors of VF arrest (and 59% of all arrest survivors) were resuscitated by medics with aggressive ALS measures, but 80% had very poor neurologic outcomes and 50% died within a year of hospital discharge. Even the need for only additional defibrillation by medics worsened neurologic outcome by a factor of 2.8. Conclusion: Faster response by medics, or any individual ALS intervention other than first-responder defibrillation, demonstrated no benefit in this urban population with short intervals between responder arrivals. Aggressive ALS increased the number of survivors but also decreased their neurologic quality. The benefit of rapid ALS backup to first responder/defibrillators needs further study in other systems. System performance cannot be judged without knowledge of neurologic outcome.