Why CPR Changed From A-B-C to C-A-B

If you have been trained in CPR for a very long time, you might wonder why the order of steps changed to put the breaths after the chest compressions. Why did CPR change from A-B-C to C-A-B?

In 2010, the American Heart Association's (AHA) Guidelines for CPR rearranged the order of CPR steps. Today, instead of A-B-C, which stood for airway and breathing first, followed by chest compressions, the AHA teaches rescuers to practice C-A-B: chest compressions first, then airway and breathing.

Blood Flow is Top Priority

Just like you can hold your breath for a minute or two without having brain damage, people in cardiac arrest can go a minute or two (actually a lot longer than that) without taking a breath. What they 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.

Removing Delays

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 AHA explained it this way:

"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 the blood gets flowing again. That's a good trade.

Chest Compression Basics

Chest compressions should be at least two 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 AHA Guidelines for CPR came out, the science of CPR has continued to support 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 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.