Research on the composition of ambulance crews is always fun to critique, in part because it’s generally pretty meaningless, and frequently raises more questions than it answers. That makes it great to have come across a new study, which examined cardiac arrest survival rates in Milwaukee County, for patients treated by 2, 3, or 4 (or more) paramedics.
The authors looked at 12 years of cardiac arrest data, and were able to correlate EMS cardiac arrests to hospital patients, in order to accurately track not only ROSC but survival to hospital admission and discharge. (From this aspect, at least, that makes this one of the higher-quality crew composition studies I’ve seen.) The raw numbers gave roughly similar survival-to-discharge rates for crews with 2, 3, or 4+ medics (8.7, 8.7, and 8.4% respectively). However, the percentage of each group responding to shockable rhythms was lowest in the 2-medic group (40.7%), higher in the 3-medic group (49.9%), and higher still in the 4-medic group (59.8%). Given that the shockable patients are the most savable, the 4-or-more group should have had the highest save rates…but they didn’t. This became very obvious when the researchers controlled for things known to make a survival difference (presenting rhythm, for example, or whether the arrest was witnessed): patients treated by crews with 4 or more medics had 2/3 the odds of surviving to discharge of those treated by only 2.
One explanation the researchers suggest is somewhat plausible–perhaps all those medics being present and looking for something to do result in more ALS interventions being performed, resulting in less CPR (and we all now know how important quality CPR is). Personally, I expected even the adjusted save rates to be perfectly identical, so my money is on another possibility: that there’s some other factor that causes high mortality, but happens to be associated with having more medics on scene.
For example, survival has been shown to be lower in poorer people, who are also more likely to live in an urban area–exactly the kind of place you’d expect to get a response with more medics than you need. This would mean that more medics don’t give worse care than fewer, but that their abundance is a marker for something about the individual, in the same way that ice cream sales and rape rates correlate almost perfectly–not because they are related but because they are related to some third thing (which, in the case of ice cream sales and rape rates, would be temperature).
Filed under: EMS Research
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