What is a "save"?: Outcome measures in clinical evaluations of automatic external defibrillators

Automatic external defibrillators (AEDs) represent an important technologic innovation in the management of out-of-hospital cardiac arrest. We propose the following concept: AEDs are machines with the limited task of ventricular fibrillation (VF) identification, countershock delivery, and defibrillation. They cannot be expected to produce "saves" independently. This study tested this concept by using the same AED in two different emergency medical systems: outcomes dependent upon the device should be the same in both groups, whereas outcomes dependent upon patient and system factors should be different. Paramedics, with the AED as their initial monitor/defibrillator, treated 16 cardiac arrest patients in VF; EMTs (emergency medical technicians), with the same AED, treated 17 patients in VF. There were no significant differences in the outcomes proposed to be machine-dependent: sensitivity, defined as the percentage of VF rhythm segments shocked; specificity, defined as the percentage of non-VF rhythms not shocked; and defibrillation of segments of VF to non-VF rhythms. There were, however, differences in the outcomes dependent on patient and system factors (paramedic group presented first): percent converted to a perfusing rhythm (23% vs 69%; p less than 0.05); percent admitted to the hospital (19% vs 65%; p less than 0.025); and percent discharged from the hospital (6% vs 29%; p = N.S.). We conclude that AEDs should be compared and evaluated on device-dependent outcomes and not on the basis of producing "saves".