In-Hospital Defibrillation

Are AEDs faster than manual defibrillators?

John A. Stewart, RN, MA
Seattle, WA
December 1997

A number of sources, including the American Heart Association's Textbook of ACLS, assert that automated external defibrillators (AEDs) provide a time-to-first-shock advantage over manual defibrillators. This is based on two out-of-hospital studies [1, 2], both of which maintain that EMTs defibrillate about a minute sooner on average with AEDs than with manual defibrillators. My experience with defibrillation training leads me to doubt that conclusion. My reasoning is outlined below.

In both studies the time needed to deliver the first shock was taken as the time from turning defibrillator power ON until shock delivery, power ON being assumed to occur upon arrival at the scene. Given the stressful setting and human fallibility, variations from training protocols are inevitable, but of course such variations would lead to erroneous conclusions about relative speed only if they did not occur randomly in both experimental and control groups. But based on my experience, I think it likely that such variations were not random and that the conclusion about the speed advantage of AEDs is the result of study artifact.

I have trained people to defibrillate using manual defibrillators, and I have indirectly taught AED defibrillation (in a video I made ten years ago using Physio-Control's Lifepak 200 AED). In thinking back on my training experiences, I realized that my instruction for manual defibrillators was to turn power on first, before attaching monitoring leads (at that time I was following the example of King County Washington EMS in using chest leads instead of quick-look paddles), whereas in the AED video I taught attaching the dual-function electrodes first, then turning on the device. I didn't think twice (or really even once) about this inconsistency at the time: Physio-Control's own video on the Lifepak 200 showed power ON after electrodes were attached, and no one ever questioned either procedural sequence.

Maybe the time difference in the two studies is due to how people "naturally" tend to use the devices. Just about everyone has been conditioned from an early age to expect a few seconds of lag time for an electronic display screen to warm up after being switched on. I think this tendency probably applies to using defibrillators in an emergency setting as well as to such routine activities as switching on a TV or personal computer. So perhaps this tendency leads people fairly consistently to turn on defibrillators to warm up upon arrival at the scene–as long as there is no reason not to do so. But I believe that AEDs do give EMTs a disincentive to turn them on early: an instruction in the form of beeps, a synthesized voice command, or a display message, telling them to attach the electrodes-which one would hope very few would consider necessary and many might find annoying and distracting. To avoid being told every few seconds to attach electrodes, EMTs might tend to turn AEDs on later, after the electrodes are attached.

I consider it likely that this factor accounts for a considerable portion of the difference in mean time intervals between the experimental and control groups in both studies. The finding that AEDs are faster than manual defibrillators is initially contrary to common sense (since AEDs prevent shocking during the automatic analysis period), and I have heard that the Seattle investigators were initially surprised by the discrepancy and called in a consultant from England to review the audiotapes. Though presumably nothing was found to be amiss, I think an artifact such as I describe could escape notice even with such review unless a conscious effort was made to rule it out by looking carefully at the intervals from power ON until attachment of the leads. If the investigators in the two studies did make such an effort, it would seem that they must have come up with an estimate of the time required to attach the manual defibrillator monitoring leads (and then prepare the paddles for a shock). One of the articles [2] states that this "added only a few seconds to the time to shock delivery,"; the other [1] omits attaching leads in a list of the "greater number of tasks that must be accomplished with manual defibrillators" while including tasks that would be unnecessary with use of quick-look paddles. But quantifying the delay for attachment of leads is obviously important to evaluating the claim of quicker shock delivery with the AEDs, since many (including me) would argue that the delay could have been eliminated by using quick-look paddles with the manual defibrillators.

EMT defibrillation protocols typically call for three-lead monitoring instead of quick-look paddles for initial assessment of the cardiac rhythm. My informal research into this practice indicates this was a judgment call, based on personal experience with artifact problems, by two of the first researchers on the subject of EMT defibrillation; the practice has apparently never been supported by clinical data (personal communications, Mickey Eisenberg MD and Ken Stults).

A more recent study [3] did a comparison of time intervals from arrival at the scene to first shock with what I think is a more valid method of time measurement than was used in the Stults and Cummins studies--using tape recorders turned on at the moment the emergency vehicle arrived at the scene. The data showed essentially equal median time intervals from arrival to first shock for the experimental (AED) group and the control (manual defib) group (AEDs were operated by EMTs and manual devices by emergency physicians, which admittedly complicates the picture somewhat). Looking closer, the manual defib group was significantly faster than the AED group in arriving at the initial rhythm identification--but the time gain was lost due to greater delay in delivering the shock. The authors attribute this delay in shock delivery in part to the extra time required to prepare the paddles for the shock (they were using three-lead ECG monitoring initially). Not surprisingly, I agree. If quick-look paddles had been used initially, it seems likely that rhythm identification could have occurred in roughly the same time and the shock could then have been delivered almost immediately, thus significantly shortening time to first shock.

1. Stults KR, Brown DD, Kerber RE. Efficacy of an automated external defibrillator in the management of out-of-hospital cardiac arrest: validation of the diagnostic algorithm and initial clinical experience in a rural environment. Circulation 1986; 73(4) 701-709.

2. Cummins RO, Eisenberg MS, Litwin PE, Graves JR, Hearne TR, Hallstrom AP. Automatic external defibrillators used by emergency medical technicians: a controlled clinical trial. JAMA 1987; 257(12): 1605-1610.

3. Schneider T, Mauer D, Diehl P, Eberle B, Dick W. Quality of on-site performance in prehospital ACLS. Resuscitation 1994; 27: 207-213.

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