The 2010 AHA ACLS Guidelines put forth a major change in the sequence of steps in basic life support. Unlike the A-B-C (Airway, Breathing, Circulation) of the past, the new AHA evidenced-based recommendation is C-A-B (Chest compressions, Airway, Breathing.) The new changes encompass PALS and ACLS, but do not include newborns.
The AHA and the various advisory and research committees involved in resuscitation recommend this change because it is believed that the majority of cardiac arrests occur in adults. Within the subgroup of cardiac arrest patients with a witnessed arrest and a subsequent rhythm of ventricular fibrillation or pulseless ventricular tachycardia, the critical elements are chest compressions and early defibrillaton.
With the earlier initiation of chest compressions, the AHA also recommends minimal interruption for ventilation, awaiting the completion of the first cycle of chest compressions. It should take approximately 18 seconds to complete one cycle of chest compressions.
The emphasis on chest compressions will hopefully result in more lay providers initiating CPR, even without ventilation.
In hospital providers are advised to tailor the sequence of C-A-B to the likely cause of arrest.