Best settings for biphasic automated defibrillators investigated

As the use of automated external defibrillation (AED) devices outside of hospital settings increases, the scientific medical community has not agreed on the optimal energy levels for initial and subsequent biphasic shocks. A study presented at the 2006 Society for Academic Emergency Medicine Annual Meeting, May 18-21, 2006 in San Francisco investigated both fixed and escalating biphasic energy regimes for out-of-hospital cardiac arrest.

In a randomized, controlled trial, emergency medical services (EMS) personnel or firefighters in three cities used preprogrammed LIFEPAK® 500 biphasic AED devices to treat 221 patients in sudden cardiac arrest, with 114 receiving fixed levels of 150-150-150 joules (FIXED) and 107 receiving escalating levels of 200-300-360 joules (ESC). The energy being delivered was unknown to the firefighters.

The patients had a mean age of 66 years and were 80 percent male. The event was witnessed in 64 percent of the cases and 24 percent of the patients received CPR from bystanders. Outcomes included conversion (return of QRS complexes within 60 sec), termination (removal of ventricular fibrillation (VF) for at least 5 seconds), survival, and evidence of harm.

For first shocks, the rates of termination and conversion were similar for the two regimens. For subsequent shocks, however, the rates of both termination and conversion were higher for the escalating than the fixed energy regimen. The study did not demonstrate a difference in other outcomes between the two regimens but was not powered to do so.

This is the first randomized trial to compare fixed and escalating biphasic energy regimens, and it found more successful termination of VF and conversion to an organized rhythm for secondary shocks with the escalating regimen. A much larger trial will be necessary to determine whether these differences in electrical outcomes translate to a difference in survival.

The study, "A Randomized Controlled Trial of Fixed Versus Escalating Energy Levels for Defibrillation," was presented by Ian G Stiell MD. His co-authors are Robert Walker, Lisa Nesbitt MBA, Fred Chapman, Donna Cousineau RN, James Christenson MD, Paul Bradford MD, Sunil Sookram MD, Ross Berringer MD, Paula Lank, and George A Wells PhD. This paper will be presented at the 2006 SAEM Annual Meeting, May 18-21, 2006, San Francisco, CA on Thursday, May 18, in the Plenary Session beginning at 8:00 AM in Salon 9 of the San Francisco Marriott. Abstracts of the papers presented are published in the May issue of the official journal of the SAEM, Academic Emergency Medicine.

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