CPR Research
A summary of why the AHA changed what we do...

Cardiopulmonary resuscitation has been practiced for many years. Recently new CPR Research by the American Heart Association (AHA) has shown that we may have been doing it wrong. The Journal of the American Heart Association - Circulation - in their December 2005 edition outlined and summarized the CPR research that had been underway since 2000.

Some issues were not in dispute. Sudden Cardiac Arrest (SCA) is the cause of 250,000 out-of-hospital deaths per year in the US. About 40% of out-of-hospital SCA experience ventricular fibrillation (VF). Despite decades of efforts to promote CPR science and education, the survival rate for out-of-hospital cardiac arrest remains low worldwide, averaging 6% or less.

The reasons for this low survival rate are multifaceted:

  • Early CPR is necessary for a positive outcome but this requires laypersons to start CPR in many cases. Only 1/3 of witnessed SCA outside of the hospital did a layperson initiate CPR.
  • Many Laypersons feel that CPR is too complicated. There were different procedures for different ages
  • CPR Research has shown that our initial training was inadequate. There was poor skills retention
  • There was too much ventilation and frequent interruption of compressions.
  • The lay public was afraid of transmitted diseases.

Clearly things needed to be changed.

With the 2000 AHA guidelines we were taught that early defibrillation was the key to survival. However, CPR research has shown that the delays in compressions rapidly decreased the survival rate. Survival rates in witnessed SCA decrease 7 to 10 % per minute without CPR. With CPR the survival rates improve slightly with the decrease becoming 3 to 4 %. This assumes that defibrillation will occur within 3 to 5 minutes. CPR with AED in the first 3 to 5 minutes has shown to have 49 to 75 % survival rates.

This indicates to me that we need CPR early in the sequence. If the SCA is witnessed then early AED is recommended. IF there is delay of more than 4 minutes, 2 minutes of compressions with ventilations are recommended to perfuse the tissue.

It is interesting to note that no human data exists for the optimum ratio of compressions to ventilations for patients of all ages. The 30:2 ratio is based on a consensus of experts rather than clear evidence. It is designed to increase the number of compressions, reduce the likelihood of hyperventilation, minimize interruptions in chest compressions for ventilation, and simplify instruction for teaching and skills retention.

Push hard and fast is the new mantra. 100 compressions per minute is the recommended rate. The checking of a pulse during compressions is disfavored since venous blood flow could be present with poor compressions.

1 shock versus 3 shocks

One of the major changes to the cpr guidelines was the reduction of the stack of 3 shocks for an AED to a single shock followed by CPR.

  • 2000 guidelines were based on monophasic defibrillators which had low first shock effectiveness
    Modern biphasic defibrillators have much higher first shock effectiveness and thus a much higher success rate to convert ventricular fibrillation. Subsequent shocks, if the first was unsuccessful, are unlike to convert the patient out of VF without compressions.
  • As of 2005, there are no published studies on 1 versus 3 shocks.
    • Animal studies show that interruption of compressions decreases survival rates
    • In 3 shock cases, compressions were only be performed 50 to 75 % of the time.
  • In 2005 most commercial AEDs took, on average, 37 seconds to deliver the first shock and first post-shock compressions. This delay was difficult to justify since modern biphasic AEDs are usually 90 % successful in converting VF.

What does this mean to you? The AEDs that we used in 2000 were frequently monophasic (shocking in only one direction) and were often not effective in converting ventricular fibrillation into a perfusing rhythm. Modern biphasic AEDs (shocks first in one direction and then reverses the charge) are much more effective at converting VF. Failure to convert means that further shocks are unlikely to succeed.

It is interesting that as of 2005 there are no studies that show if 1 or 3 shocks are better. What is known that the long delay in compressions during a 3 shock scenario decreases the chance of survival.

CPR Research has shown that in cases of suspected cervical spine trauma that a mechanical device such as a C-collar is not recommended. Manual cervical spine immobilization is recommended using a jaw thrust to open the airway. It is felt that the use of a c-collar could prevent proper airway management.

Foreign Body Airway Obstruction (FBAO)

The CPR research data on choking is largely retrospective and anecdotal. For responsive adults and children > 1 year of age with severe FBAO, case reports show the feasibility and effectiveness of back blows or “slaps,” abdominal thrusts, and chest thrusts. Case reports 1 large case series of 229 choking episodes report that approximately 50% of the episodes of airway obstruction were not relieved by a single technique. The likelihood of success was increased when a combination of back blows or slaps, abdominal thrusts, and chest thrusts were used

CPR in Children and Infants

The single biggest change in CPR in children relates to the use of AEDs. The age limitation was essentially removed and lowered to 1 year old. Modifications in pad placement, size and energy have been made. VF is uncommon in pediatric patients. Only 5 to 15% of SCA in pediatrics is in VF. The lowest energy for pediatric patients is unknown. The AHA has no recommendation for AED use for infants under 1 year of age.

Urban Myths?
There has been a host of myths surrounding the of AEDs. One common myth was the risk of fire with nitroglycerin patches. This sounded likely but there are no reported case of an AED causing a fire due to a nitro patch exploding. The most likely result of a medication patch is that it might divert energy away from the heart.

However, there have been some reported cases of fire from the use of manual defibrillators and oxygen supply tubing. If free oxygen was blowing across the patient's chest while a pad or paddle was poorly attached to the patient, flash fires have been reported.

This was a brief summary of the changes in CPR research from the 2005 guideline conference. The full study can be downloaded from the American Heart Association as a PDF file. Click here to view the AHA 2005 Guidelines download page (warning! Link opens a new window)

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