CardioPulmonary Resuscitation is historically fairly new; Safar et al showed in the 50's it could be effective as a method, and it became more widely used during and after Viet Nam. (About the only good thing that wars do is further medical science) It has evolved and changed over the years, the most recent update in technique was from the American Heart Association a couple years ago.
Put simply, it's a way of maintaining some circulation to critical areas (heart muscle, brain) until either the heart re-starts, or more definitive medical measures can occur.
It is done by compressing the sternum enough (generally, 2 inches in adults) to squeeze the left ventricle of the heart, pushing blood out the aorta and hopefully to needed areas. Ventilation of the lungs occurs either by mouth-to-mouth, or preferably with a mask/bag, like an Ambu bag. The ventilation part of CPR has been somewhat 'downgraded' in importance, at least in CPR lasting less than 5 minutes.
Now the sobering part: just how effective is CPR? The quick answer is 'better than nothing'. If the heart stops pumping, fewer than 1% will spontaneously re-start. So statistics have been compiled over the past years, and it divides the event into ones that occur out in the general community, and those occurring in a hospital.
As you can imagine, the ones that occur in a hospital have a higher recovery rate. Here's the statistics compiled by the AHA:
|Statistical Update||Out-of-Hospital Cardiac Arrest||In-Hospital Cardiac Arrest|
|Incidence||Bystander CPR |
A couple things stand out: Only 40 percent of cardiac arrest occurring out of hospitals have CPR performed. This is somewhat skewed, many are not witnessed, the person is alone, driving, or something else where no one is around. Of those where CPR does occur, the survival rate is roughly 10%.
You notice also the survival rate in children is much higher. Likely because fewer of them have an underlying heart condition, the heart stoppage is more likely from an accident, or electrical shock, hence the heart is more likely to re-start.
This pretty much correlates with my personal experience. I've probably done more than 200 CPR procedures, only two were not in a medical center. Neither of those two survived.
Now, what is a lot more successful is defibrillation. Once only available in hospitals, now many areas have portable defibrillators in public places. The principal is that a electrical shock sent through the heart muscle can cause the heart's own electrical system to start working. Statistics are not available yet, but it appears to be much better than only CPR.
I once did a series of measurements of cardiac output (how much blood is being pumped by the heart) during CPR. We used the thermodilution method, and found the average cardiac output was 0.4 liters per minute during CPR. Normal output is around 4-6 liters per minute.
What that tells me is that extended CPR, lasting longer than 15 minutes without the heart re-starting, will rarely be successful. Also, the brain will be without oxygen for that period, and will be damaged. I'm certainly not suggesting that you not do CPR, it should be done until medical personnel arrive. Every once in awhile it'll work and a life is saved.
So CPR has a low success rate, but it's a lot better than nothing.
If you're interested, the current guidelines can be found here: