Why did CPR change from A-B-C to C-A-B?

How the American Heart Association Rearranged CPR

Mouth to Mouth
Mouth to mouth. (c) Stockbyte/Getty Images

Question: Why did CPR change from A-B-C to C-A-B?

In 2010, the CPR Guidelines rearranged the order of CPR steps. Today, instead of A-B-C, which stood for airway and breathing first followed by chest compressions, the American Heart Association teaches rescuers to practice C-A-B: chest compressions first, then airway and breathing. When the recommendations were released, many folks asked: why did CPR change?

Answer: Just like you can hold your breath for a minute or two without having brain damage, patients in cardiac arrest can go a minute or two (actually a lot longer than that) without taking a breath. What cardiac arrest patients really need is for that blood to get flowing again.

Any delay in blood flow reduces survival. Rescue breathing almost always delays chest compressions. Even if breathing first was important (which it's not), it introduced delays that were never intended.

When rescuers are worried about opening the airway and making an adequate seal--plus the "ick" factor and possibly digging a CPR mask out of a purse or briefcase--the delay can be significant. All that extra time was getting in the way of the real help: Chest compressions.

In its summary of the changes, the American Heart Association explained it this way:

In the A-B-C sequence chest compressions are often delayed while the responder opens the airway to give mouth-to-mouth breaths or retrieves a barrier device or other ventilation equipment. By changing the sequence to C-A-B, chest compressions will be initiated sooner and ventilation only minimally delayed until completion of the first cycle of chest compressions (30 compressions should be accomplished in approximately 18 seconds).

By starting chest compressions first, the patient only has to hold his breath an extra 18 seconds while blood gets flowing again. That's a good trade. Moving blood along, even blood with arguably diminishing amounts of oxygen, is the most important function of CPR. The 2010 CPR Update really put chest compressions front and center.

Chest compressions should be at least 2 inches deep for adult patients and should be delivered at a rate between 100-120 per minute. Deliver chest compressions too slow and there will never be enough blood pressure to reach the brain adequately. Deliver them too fast and you risk not allowing enough blood to return to the chest before the next compression.

Since the 2010 CPR Updates, the science of CPR has supported chest compressions in lieu of rescue breathing. Hands only CPR, once only for the uninitiated rescuer, is now the standard of care. Even some professional rescuers now have removed rescue breathing from CPR. When rescuers do provide artificial breathing, they aren't as likely to do advanced procedures, opting instead for more basic ventilation.


Field JM, Hazinski MF, Sayre MR, Chameides L, Schexnayder SM, Hemphill R, Samson RA, Kattwinkel J, Berg RA, Bhanji F, Cave DM, Jauch EC, Kudenchuk PJ, Neumar RW, Peberdy MA, Perlman JM, Sinz E, Travers AH, Berg MD, Billi JE, Eigel B, Hickey RW, Kleinman ME, Link MS, Morrison LJ, O’Connor RE, Shuster M, Callaway CW, Cucchiara B, Ferguson JD, Rea TD, Vanden Hoek TL. "Part 1: executive summary: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care." Circulation. 2010;122(suppl 3):S640–S656.

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