Posted by Bob Trenkamp on 07/20/2012

Well, it depends...

Was your arrest witnessed?
If there's nobody else around when you have your cardiac arrest - or if there is someone else around and they don't notice that you have died - you have a 3.9% chance of getting out of the hospital with your major brain functions intact. How often does this happen? More than half of all out-of-hospital ("OOH") arrests are unwitnessed.

If a bystander saw you arrest, you have 15.2% chance of survival with brain intact - that's nearly four-times better odds. The moral of this factoid is that you need to always have someone around, and that person needs to know how to tell if you've just arrested. More than one-third of all OOH arrests are witnessed by a bystander.

If a 911 responder got there in time to see you arrest - maybe someone called 911 because you weren't looking all that good a few minutes ago - you have an 18.6% chance of survival with major brain functions intact. A little more than 10% of the time, a 911 responder sees the arrest happen.

Many of you are asking yourselves, "Why is it that my odds of survival only improve by 22% when it's the professionals see the arrest, as opposed to an ordinary bystander?" Good question. Read on.

Who started performing CPR on you?
In one third of the cases a bystander initiated CPR, and in two thirds of the cases a 911 responder initiated CPR. When the 911 responder initiated CPR, 8.7% survived. When the bystander initiated CPR, 11.3% survived - a 41% improvement. That's most likely because the bystander began CPR before the 911 responder arrived, and immediate CPR is essential.

Who first applied the AED or Monitor to your right upper chest and left side chest wall?
An overwhelming 96.3% of the arrest victims had an AED / Monitor applied by the 911 responder, and only 3.7% had one applied by a bystander. When the 911 responder applied the monitor, 9.1% survived. When the bystander applied the AED, 23.5% survived.

Why did so few AEDs get applied by bystanders? First of all, there aren't enough AED's nearby in most locations. Second, fewer than one-third of the bystanders will perform CPR, so why would we think that all bystanders would apply the AED, even if AED's were everywhere?

Why did the bystanders get such better results? An AED promptly applied works far, far better than one applied after the 911 responder gets there.

How representative are these numbers?
Mileage does vary. If you arrest on a farm, your chances of surviving are near zero. If you are in the passenger concourse in the Pheonix, AZ airport your chances of surviving are 75% - an average value for the past ten years. The Phoenix airport gets such good results because there are lots of trained people and AED's nearby, and they practice.

Interestingly enough, the existence of such a wide range of outcome probabilities tells us that most places can do far better than they do.

What does all this mean?

  1. You do not want to have a cardiac arrest, and you really don't want to have an unwitnessed one.
  2. If you get immediate, high-quality CPR (chest compressions of two inches or more, 100-120 times a minute with almost no interruptions and with no interruption longer than five seconds) and if you get defibrillated promptly - say, within three minutes of the arrest - you can expect your survival odds to be far, far higher than otherwise.
  3. Get a personal AED, unless you live alone.

How long will a bystander / 911 responder have to do CPR?
Somewhere in the five-to-fifteen minute range - sometimes longer. It's going to take the person who witnesses the arrest a few moments to figure out what is going on, it's going to take a few moments to get a phone and call 911, it's going to take a few moments to tell the 911 operator where you are / what's wrong / what you are doing / what you need, it's going to take a few moments for the operator to decide which ambulance is going to respond and to contact them, and so forth. The ambulance probably won't be rolling until somewhere between two and four minutes after the arrest.

How long can a bystander perform adequate CPR?
Extremely few bystanders can perform adequate CPR compressions for three minutes. Ouch!

If the bystander who came to your aid isn't alone, the bystanders will need to alternate, switching every few minutes. Otherwise the chest compressions will become too shallow and too slow.

If the bystander at your side is alone, he or she will have to perform chest compressions adequately until the ambulance crew arrives and takes over the compressions. Unfortunately, this is not possible using the chest compression method that we learn in all certificated CPR courses (AHA, ARC, etc.) The lone bystander needs to stand by your side (you're flat on your back on a hard, flat surface with your head tilted back slightly), facing the direction your legs are pointing, has to take off his or her shoes, and has to place the heel of the foot at the CPR point so that he / she can compress your chest at an adequate rate and depth until the ambulance crew takes over. The bystander needs to be very careful to not put pressure on that thingy at the bottom of the breastbone. (the Xiphoid process)

Will the ambulance crew know how to do this?
Probably not, but there will be multiple people arriving with the ambulance and they can take turns. (Many ambulance services dispatch two ambulances to cardiac arrest calls, and each ambulance has at least two crew members.) And even if they do know, the odds of their being able to use this technique are slim - it's not part of the healthcare provider Basic Life Support CPR certification course that they have to pass, and absent a directive from that ambulance service's Medical Director, they will have to use the hands method. Unfortunately, there are too many situations where an EMTs or Paramedic has to work on the patient alone while his partner drives. There are also a few who haven't embraced the importance of deep, rapid, and uninterrupted chest compressions.

What does the "only 22% improvement" question from the first point tell us?
It tells us that the average bystander can perform CPR at a level that yields a result that's only about 80% of what the average, trained, certified, do-it-all-the-time professional can achieve. That's pretty impressive.

How big a deal is this? It only comes into play when there's a lone bystander helping.
Right you are. There is 'only' up to a thirty-six percent chance that your cardiac will be treated using a method that cannot do the job.

Omitting the "heel CPR" method from the AHA, ARC, etc. curricula is the same as telling someone whose foot is under the tire of a car that just ran over his foot, "Pick up the car, move your foot, and set the car down gently."

Where did all this data come from?
Its all in Table 3 in the CDC publication of the CARES data. You can find it at

Where can I learn more about the heel method?
Go to and click on the "for past trainees" link in the left-hand column. You can download the class video. It's not slick and polished, but it contains the information. The video runs about 35 minutes, and you'll learn Bystander CPR, AED use, dealing with choking, and stroke recognition.