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I have not had a CPR (Cardiopulmonary resuscitation) class in 10 or more years, but I used to take them all the time (like yearly). For one person CPR the ratio of compression to breaths was always changing. In the US there were two major providers of approved CPR training, It was not unusual for both to have different ratios as "the correct value" at the same time, and the following year, one or both would be different.

How are the ratios determined? What impact if any do minor changes in the ratio have?

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    <comments removed> Please stop answering questions in comments. Comments do not provide the features to properly vet information. If you have an answer, please post it below. Thanks. – Robert Cartaino Apr 6 '15 at 13:41
  • @JamesJenkins Could you change the title to less ambiguous, such as 'How are the CPR ratios determined and what's the impact of minor changes?' or 'How are the CPR ratios determined and what do they keep changing over the time?'? – kenorb Apr 20 '15 at 15:34
  • @JamesJenkins Could you confirm please in meta whether my deleted answer (after edit) was answering your question, or not? – kenorb Apr 24 '15 at 11:36
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Note: The following is excerpted from an article written in 2005. For lay (Non trained) people, there are more updated recommendations. The following is an example of the process, not the current recommendations.

To be effective, CPR must restore adequate coronary and cerebral blood flow. Interruptions in chest compressions lower coronary perfusion pressure and decrease rates of survival from cardiac arrest. In the first minutes of VF SCA, ventilation does not appear to be as important as chest compressions, but it does appear to contribute to survival from prolonged and asphyxial arrest. Certainly the ventilation rate needed to maintain a normal ventilation-perfusion ratio during CPR is much smaller than normal because pulmonary blood flow is low.

That is one of the opening paragraphs from this article published on the American Heart Association (AHA) website from 2005, regarding CPR evaluation and recommended changes. (VF SCA = Ventricular Fibrillation Sudden Cardiac Arrest)

As a summation, a group of scientists and heart experts (281 experts over 36 months) gathered to review all the study and epidemiological data regarding survival rate in witnessed SCA. They reviewed the (then) current survival rates, sequence and priorities in CPR to see how differences affected the survival rate. There are 57 articles cited throughout the article that are all listed with links.

One of the biggest factors was that few people received early CPR, and those that did, it wasn't always effective CPR. Some of the factors that they found were that chest compressions were inadequately performed, slow, and often interrupted for too long for rescue breaths, especially among lay CPR performers (Non EMS trained). This resulted in inadequate cerebral blood flow and cardiac output.

Once they determined that, the following excerpt explains how they evaluated the recommended changes (at that time, this is a 2005 publication.)

Mathematical and animal models showed that matching of pulmonary blood flow and ventilation might be more appropriate at compression-ventilation ratios higher than 15:2. There was concern, however, particularly among pediatric experts, that inadequate ventilation rates could reduce survival from pediatric and asphyxial (eg, drowning) arrest. To achieve optimal compression rates and reduce the frequency of interruptions in compressions, a universal compression-ventilation ratio of 30:2 for all lone rescuers of victims from infancy (excluding newborns) through adulthood is recommended by consensus, based on integration of the best human, animal, manikin, and theoretical data available. The 30:2 ratio is recommended to simplify training in 1-rescuer or 2-rescuer CPR for adults and all lay rescuer resuscitation. A compression-ventilation ratio of 15:2 is recommended for 2-rescuer CPR (a skill taught chiefly to healthcare providers and lifeguards) for infants and children (to the onset of puberty). This recommendation will result in the delivery of more rescue breaths per minute of CPR to victims with a high prevalence of asphyxial arrest.

So basically, a panel of experts gets together and reviews current literature and reports on survival from both field and hospital based sources. Along with that they review changes and practices that have been implemented (There is reference to early Automatic External Defibrillator {AED} devices being a key factor in survival rates) since the last recommendation. They pair this with animal and computer modeling to determine what should used for compression rates and compression/breath ratios.

As far as the differences, I do not know how to account for those other than people using outdated information, or not following guidelines. Here in the United States, (as far as I know), all CPR certification falls under the guidelines of the AHA.

  • For completeness, it's probably best to mention what the latest recommendations are. Only seeing 30:2, without seeing the modern figure, will make 30:2 "stick" – Alexander Jan 24 '18 at 0:48
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In Europe we use 30/2 for adults and 15/2 for children.

For children heart problems are rare, so the focus lies on breathing (we also start with 5 breaths). With adults the focus lies on chest compressions, hence the double amount.

There is a lot of research going on and as a result of the research, the guidelines are changed, each 5 years. (Last time the dept of the compression increased and the frequency went up.) We hope to receive the new guidelines in 2016.

All ERC (European Resuscitation Council) trained instructors should use the same guidelines in their courses.

The actual survival chance has increased a lot the last 20 years (if CPR is started with 6 minutes). Two pieces of equipment have helped. First the mobile phone (no delay in finding a phone so professional help can be summoned as soon as possible). And the use of the AED.

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