Cardiopulmonary Resuscitation (CPR) is an emergency procedure combining chest compressions and artificial ventilation to manually maintain blood flow and oxygen supply to the brain and other organs when the heart has stopped. Immediate action can double or triple a person’s chance of survival following sudden cardiac arrest. Understanding the correct steps for basic life support is a necessary skill. The procedure has evolved significantly; the traditional method was known as “ABC,” but current guidelines prioritize a different sequence for better patient outcomes.
The Historical Meaning of ABC
For decades, the universally taught sequence for CPR was represented by the mnemonic ABC, standing for Airway, Breathing, and Circulation. The original protocol directed a rescuer to first ensure the victim’s airway was open, as a blocked airway prevents ventilation. This was considered the most immediate threat to life.
The second step, Breathing, involved checking for respiration and administering rescue breaths if needed. Only after securing the airway and delivering two initial breaths did the rescuer proceed to Circulation. Circulation involved initiating chest compressions to move oxygenated blood through the body. While this order made sense for respiratory incidents like drowning, it presented limitations in time-sensitive cardiac arrests.
The Modern Shift to CAB
The standard for adult CPR shifted dramatically when organizations like the American Heart Association (AHA) prioritized a new sequence: CAB. This change was officially adopted in the 2010 guidelines. The C-A-B order stands for Compressions, Airway, and Breathing.
The reason for this change was the realization that starting chest compressions immediately is the most effective action to improve survival rates in sudden cardiac arrest. An adult who collapses often has enough residual oxygen in the bloodstream to sustain the brain briefly. The immediate need is to circulate this existing oxygenated blood to the brain and heart. The original ABC sequence introduced delays to chest compressions while the rescuer focused on airway and breathing, wasting precious seconds of blood flow.
Detailing the Current CAB Steps
The modern CAB sequence focuses on continuous, high-quality chest compressions. The first step, C (Compressions), requires the rescuer to place the heel of one hand in the center of the victim’s chest, with the other hand placed on top. Compressions must be delivered hard and fast, at a rate between 100 and 120 per minute. For an adult, the depth should be at least 2 inches (5 centimeters) but not exceed 2.4 inches (6 centimeters). Allow the chest to fully recoil after each compression to ensure blood returns to the heart.
After 30 compressions, the rescuer moves to A (Airway) and B (Breathing) to deliver oxygen. The airway is opened using the head tilt-chin lift maneuver, which gently tilts the head back while lifting the chin. This action moves the tongue away from the back of the throat, preventing obstruction. Following this, the rescuer administers B (Breathing) by giving two rescue breaths.
The standard ratio for trained rescuers is 30 compressions followed by 2 breaths (the 30:2 ratio). Each breath should be a steady blow lasting about one second, and the rescuer should observe the chest rise to confirm success. This 30:2 cycle is repeated until emergency medical services arrive or the victim shows signs of life. For untrained bystanders, a hands-only approach (continuous compressions without breaths) is recommended to maximize the speed of the first compression.