Happy birthday to you...

CPR!  Yup, that's right, CPR turns 50 years old today.

Whoops.  I mean 38.  Again.

Seriously, though, on this day in 1960, the official guidelines for CPR were adopted by the American Heart Association.  I thought this was kind of cool, seeing as I've been teaching it for roughly ten years now and have seen the protocol change even in that short window of time.

CPR, or cardiopulmonary resuscitation, is an emergency intervention used to maintain the flow of oxygenated blood in a person (or patient, victim, etc) when the person's heart stops working effectively.  Typically this would be used when someone goes into cardiac arrest or encounters some other life-threatening situation that stops the heart. 

I was surprised to learn that the use of artificial breaths (ie, mouth-to-mouth) and chest compressions has been around for several hundred years.  As early as 1760, artificial breathing was touted by the Parisian Academy of Sciences as part of a protocol to revive drowning victims.  Successful use of the practice was seen years earlier, when Dr. William Tossach used mouth-to-mouth resuscitation to revive a miner.  Depending on the sources I found, dates for this varied wildly between 1732 and 1771, though the most commonly cited appears to be 1743.  Dr. Friedrich Maass utilized chest compressions to revive a teenager in 1892 (again, some variation in date based on source).  There is also evidence that different forms of resuscitation may have been used earlier in history.  Check out some of the earliest methods here and here.

So what did CPR in 1960 look like?  The major development in 1960 was the establishment of a protocol that used "closed-chest cardiac massage."  Basically, the protocol focused on pressing on the chest to circulate blood, which was oxygenated by the delivery of artifical breaths.  This use of chest compressions and breaths differed from the then-commonly-used Holger-Nielsen Technique that was utilized from 1911 through the 1950s.  

In recent times, the AHA has changed its CPR protocol, such as the ratio of compressions to breaths delivered in a minute.  In 2005, the AHA recommended the use of 'Hands-Only CPR' for bystander-intervention in an emergency.  Three years later, following the publication of its recommendation panel in a peer reviewed journal, the guideline was expanded. 

Basically, this revision eliminated the use of artificial breaths for the lay person, or bystander.  The change was thought to focus on three advantages (in no significant order):
1) Eliminating bystander hesitation to intervene (by removing a step that requires a barrier like a mask to be performed safely)
2) Focusing on the delivery of high-quality, rapid compressions at a rate of 100 per minute (think about the beat to 'Staying Alive') is used as a temporary intervention until EMS arrives
3) Making the protocol easier to learn, thus increasing the chances a person will receive CPR care. 

Subsequent studies have shown that Hands-Only CPR requires more effort on the part of the rescuer, but quality of CPR has improved.  Studies also showed that removing the artificial breaths did not change the outcome of survival or the flow of oxygenated blood in the subjects.  At present, no studies in human patients or animal models support the claim that reducing or eliminating breaths is harmful.

Although this idea seems counter-intuitive, it actually makes sense from a biology standpoint.  You may remember from basic biology that oxygen is carried by hemoglobin on red blood cells.  To describe a simplified loop, the red blood cells squeeze their way through capillaries in the lungs and pick up fresh oxygen.  They then tumble through the bloodstream via arteries until they reach a new capillary bed, this one in tissues. A second exchange happens, and the oxygen is delivered to the rest of the body.  The red blood cells then return through veins to the lungs, where they pick up more oxygen.  Check out a handy diagram here.  Venous blood doesn't have 'zero' oxygen, it just has oxygen present at a lower pressure than that of arterial blood.

Interestingly, delivery of 100% oxygen doesn't actually increase the amount of oxygen in a person's blood or tissues.  The advantage of 100% oxygen delivery is that it increases the amount of oxygen in the lungs.  When a person becomes unconscious and is unable to breathe, the amount of oxygen available to them is largely a function of the amount of oxygen in their lungs (ie, lung volume, and the amount of oxygen in small sacs called alveoli that help mediate gas exchange).  The air we breath is typically about 20% oxygen.  Increasing this percentage facilitates the exchange of oxygen to hemoglobin as the blood pumps through the lungs, but it doesn't significantly increase the amount of oxygen in the blood itself.  There are even situations when delivery of 100% oxygen (or hyperoxia) can be detrimental - email me if you want to discuss that and we can chat. It's a fascinating field of research.

So, intuitively, if the blood is pumping through the lungs as a result of hands-only CPR, it will pick up some oxygen as it passes through the alveoli and circulate it during the intervention (lungs have a residual volume unless they're collapsed).

Likely the biggest advantage of hands-only CPR is that it dramatically improves the odds that a person in cardiac arrest will receive CPR intervention.  The technique is easy to learn and reduces the need for a mask to mediate safe contact between rescuer and victim.  CPR alone actually has a low rate of success in reviving adults, and is meant to be a primary, temporary intervention until expert care is available.  The introduction of defibrillation confers significantly higher survival advantage than CPR alone, even when the shocks are delivered by non-healthcare professionals.

Current AHA CPR guidelines are summarized neatly here (or here in full, if you want to read a lot of journal articles).  Italics not mine.
"When an adult suddenly collapses, trained or untrained bystanders should—at a minimum—activate their community emergency medical response system (eg, call 911) and provide high-quality chest compressions by pushing hard and fast in the center of the chest, minimizing interruptions (Class I).

  • If a bystander is not trained in CPR, then the bystander should provide hands-only CPR (Class IIa). The rescuer should continue hands-only CPR until an automated external defibrillator arrives and is ready for use or EMS providers take over care of the victim. 
  • If a bystander was previously trained in CPR and is confident in his or her ability to provide rescue breaths with minimal interruptions in chest compressions, then the bystander should provide either conventional CPR using a 30:2 compression-to-ventilation ratio (Class IIa) or hands-only CPR (Class IIa). The rescuer should continue CPR until an automated external defibrillator arrives and is ready for use or EMS providers take over care of the victim. 
  • If the bystander was previously trained in CPR but is not confident in his or her ability to provide conventional CPR including high-quality chest compressions (ie, compressions of adequate rate and depth with minimal interruptions) with rescue breaths, then the bystander should give hands-only CPR (Class IIa). The rescuer should continue hands-only CPR until an automated external defibrillator arrives and is ready for use or EMS providers take over the care of the victim."
--directly quoted from Sayre, MR. et al. 

Check out an instructional video here.  There's also a video of the American Red Cross Science advisor's lukewarm assessment of hands-only CPR here.  (One specification he mentions is that full CPR is more effective in children.  In the interests of keeping this post to a reasonable length, I've chosen to focus on adults.)

I am interested to see if the recommendations will change for primary responders such as lifeguards or even EMS, to further accommodate Hands-Only CPR.  In my effort to look at primary sources, I noticed that many of the studies I read used animal models instead of humans.  This is necessary for controlled conditions and physiology, but the differences between real human patients (huge amount of variables) and identical animals (minimized variables) does leave some questions as to the benefits of ventilation in cardiac arrest.  

However, at the most basic level the take away of the AHA's recent change is that early intervention can increase a person's chance of survival in case of emergency.  

So, awesome readers, to celebrate CPR's birthday, get out there and find a class in your community.  Help ensure this skill continues to save lives!

Have a comment about the history of CPR, current guidelines, or any of the science I've mentioned above?  Leave one!

1 comment:

  1. wow that was super informative. Thanks! I feel so much smarter!