Despite the limitations of prehospital EMS research enumerated above, there have been a number of important, highly successful EMS studies that have helped inform practice. The Ontario Prehospital Advanced Life Support (OPALS) study, for example, funded by the Canadian government, is systematically examining a series of prehospital treatments using a sequential before/after design. The first major OPALS study examined the impact of adding automated external defibrillators (AEDs) to improve treatment for cardiac arrest. A subsequent study compared outcomes achieved by rapid defibrillation programs versus the addition of ALS (primarily endotracheal intubation and administration of cardiac medications). This study, conducted in the Canadian province of Ontario, was the largest multicenter controlled clinical trial ever conducted in a prehospital setting. OPALS examined 5,638 Toronto-area patients who had out-of-hospital cardiac arrest—1,391 when the area had only a rapid defibrillation program and 4,247 after it had instituted full ALS care. The researchers reported that “the addition of [ALS] interventions did not improve the rate of survival after out-of-hospital cardiac arrest in a previously optimized emergency-medical-services system with rapid defibrillation” (Stiell et al., 2004). The OPALS research study also assessed the incremental benefits for survival, morbidity, and processes of care that resulted from the introduction of prehospital ALS programs for patients with major trauma and respiratory distress. In addition, researchers conducted an economic evaluation of ALS programs by estimating the incremental cost per life saved and per quality-adjusted life year.

The largest EMS clinical study completed in the United States to date is the Public Access Defibrillation (PAD) trial, which involved 19,000 volunteer responders from 993 community units in 24 North American (U.S. and Canadian) regions. The primary objective of the study was to determine whether the use of AEDs by response teams composed of volunteer laypersons who were also trained in cardiopulmonary resuscitation (CPR) would increase the number of survivors among patients with out-of-hospital cardiac arrest. The study was supported by approximately $16 million in funding, with $10.5 million from the National Heart, Lung, and Blood Institute; $3.5 million from the American Heart Association; and roughly $3 million in donated AEDs, supplies, training mannequins, and other equipment from several manufacturers. This strategy of funding from a variety of sources is common in EMS studies. The PAD trial found that the rate of successful cardiac resuscitation from witnessed out-of-hospital cardiac arrest due to ventricular fibrillation was higher when the victim received treatment by community volunteers trained to perform CPR and also equipped with an AED as opposed to similarly trained volunteers who did not have an AED.

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