Tuesday, June 19, 2012

Response Rates of Emergency Medical Services and Mortality

A recently published article looks at the association between reduced emergency medical system (EMS) response time and the mortality outcomes of patients.  You may be asking, "Well, why does it take a study to show that?"  It would seem logical and intuitive that faster response times are associated with better outcomes.  Many municipalities and others responsible for local EMS units have spent quite a bit of time and money trying to minimize response times.  If they did not lead to better outcomes why would we be doing such a thing?

In fact, there are many things in medical care where what is intuitive is what is done and there is not a strong evidence base to support the action.  There are many in the system who are trying to change this and move us to a more "evidence-based" medicine approach, but it takes a while.

How did this study address the question in a novel manner?  Sometimes, randomized trials are appropriate.  In this case it would be completely unethical to make it take longer to respond to some people at random.  The approach used is describe in the study's abstract which can be found here.  The author, Dr. Elizabeth Wilde, points out that some studies focusing on cardiac events have shown the expected relationship but that there was little evidence outside cardiac events and what evidence there was outside cardiac events suggested no relationship.  Why might there be no relationship when the data are analyzed?  That requires us to think about incentives and to think about who knows what.  If the caller indicates a dire emergency the dispatcher can (and has an incentive to) communicate this to the EMS unit.  This is a form of triage.  The researcher working with the data later has not idea how the dispatcher communicated with the EMS unit.  So, if the dispatcher consistently triages cases in ways that make the response times for more dire cases shorter, then those cases may do better than they would otherwise.  But if the original mortality rate for those cases was high, making it a little lower will just make it similar to the mortality rate for the ess severe cases that take longer.  Then, there will be no apparent relationship between the  time of response and the morality outcomes.

Dr. Wilde found a way to use some other data--the distance from the location of the person who called for EMS services to the nearest EMS unit--as a proxy for the response time.  People have used this type of proxy (or to use the technical term, instrumental) variable before--to show things like the effectiveness of more intense treatment for heart attacks. In that case, there was a similar concern about the severity of the condition being observable to the medical care provider but not the researcher.

In the end, Dr. Wilde found that a one minute increase in response time was associated with an 8% mortality increase one day after the incident and a 17% mortality increase 90 days after the incident.

So, now we have an evidence base for efforts to improve response time.  What is the most appropriate way to do that?  That is a separate economic, political, and normative question.  It could involve technology of locating individuals.  It could involve technology for traffic control?  It could involve enforcement of traffic rules.  Or it could involve a change in norms where people are more aware of the true costs of not moving out of the way of EMS vehicles as quickly as possible.

Regardless, the study by Dr. Wilde shows that every minute can be associated with increasing the potential to save more lives.  


  1. Nice to see, that was a interesting article.Thanks for posting me great Dr. Wilde found a way to use some other data--the distance from the location of the person who called for EMS services to the nearest EMS unit--as a proxy for the response time.
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