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Saturday, September 24, 2011

Why are the survival numbers different?

I've had several people ask me why they keep seeing different numbers for survival percentages. Here's the heart of the problem:
  1. It all depends upon what you mean by survival. In days gone by - and for very good reasons in the modern age - 'survival' meant the "return of spontaneous circulation" (Come on, folks, couldn't we just say the victim got his or her pulse back?)
  2. Unfortunately, getting your pulse back doesn't always leave you at the same station. The difference is your CPC score:
    • CPC = 1 means you have no significant neurological deficit.
    • CPC = 2 means you are able to perform the activities of daily living, perhaps with some minimal accomodation.
    • CPC = 3 means you have some severe neurological deficit that interferes to varying degrees with your ability to perform the activities of daily living.
    • CPC = 4 means you are in a coma.
  3. If you are measuring survival in terms of getting a pulse back, you include all CPC levels.

    • If you are measureing survival in terms of surviving - i.e., being able to perform the activities of daily living, you include on victims who are at CPR levels 1 & 2.

    • If you measure 'getting your pulse back' you will find that 9/6% of cardiac arrest victims in the CARES database do so. If you measure 'being able to perform the activities of daily living' you will get a survival number closer to 6.5%.

Be Annoying: It could save a life

The CDC's publication of five years of CARES data underscores the importance of time.

On a sample of 31,583 cardiac arrest victims, a Bystander applied the AED only 3.7% of the time, and the 911 Responder applied the AED the other 96.7% of the time. Twenty-three percent of the people to whom a Bystander applied an AED survived, and nine percent of the people to whom the 911 Responder applied the AED survived.

This doesn't mean that Bystanders are two and a half times better at applying AEDs. It means that the Bystander was able to get an AED on the victim sooner, if there were one there. (These numbers won't tie exactly to the CARES ROSC data because they have been adjusted to eliminate the victims who didn't die but who weren't independently able to perform the activities of daily living after the incident.)

Why did the Bystander only apply the AED in 3.7% of the cases? The most likely reason is that there wasn't an AED near the scene of the cardiac arrest. Other possible reasons are the AED was too far away, and the Bystander was alone, performing CPR, or the bystander didn't know how to use an AED. I'll bet there was at least one case in the database where there was a clearly-marked AED in a case within 20 feet of the arrest, and the Bystander was too freaked out by what was going on to recognize it.

So what does this have to do with being annoying? Don't worry about how uncomfortable you might feel doing this - it won't be as uncomfortable as a colonoscopy - every time you walk into a store, ask the store personnel where their AED is. Ask the editor in chief of your local newspaper to publish a list of the public places where there isn't a public-access AED. Call the local TV and radio stations and get them on the case. And get your friends and family to do the same. and please don't assume someone else will do this: it's the cumulative effect of a lot of us asking that will get the job done.

Yes, there is a lot more we all could do, but let's just all focus on being annoying from now through the end of October: October is Sudden Cardiac Arrest Awareness month...and that would be a really good month to get an AED for your home, if you can. That's where two out of three arrests happen.

Check back in a day or so - the next posting will take some of the mystery out of AED details.