The “ABCs of life support” represent a fundamental and systematic approach to emergency response, providing a structured sequence for rescuers to follow when a person is unresponsive and not breathing normally. This protocol is the basis of Basic Life Support (BLS) and guides immediate actions aimed at maintaining oxygen supply and blood flow to preserve brain function until advanced medical help arrives. The principles embodied in this sequence are recognized globally as the first line of defense against sudden cardiac or respiratory arrest. Following this standardized process significantly increases the chances of survival.
The Foundational Principle of Basic Life Support
Basic Life Support (BLS) is the level of medical care provided to victims of life-threatening emergencies until advanced medical help is available. Historically, the BLS sequence began with Airway and Breathing, but this often delayed the most critical action for sudden cardiac arrest. The modern, evidence-based sequence for adult CPR has shifted to C-A-B: Circulation, Airway, and Breathing. This change prioritizes prompt blood flow because, in the first few minutes of cardiac arrest, the blood still contains enough oxygen. Beginning with compressions ensures that oxygenated blood reaches the brain and heart with minimal interruption.
C – Immediate Circulation and Chest Compressions
Circulation, or “C,” is the first and most emphasized step in modern adult BLS, initiated before addressing the airway or breathing. The primary goal of chest compressions is to manually pump blood through the body, temporarily replacing the heart’s function to deliver oxygen to vital organs. Before starting compressions, the rescuer must check for responsiveness and immediately call emergency medical services if the person is unresponsive or only gasping.
To perform high-quality compressions, the rescuer places the heel of one hand on the center of the chest (the lower half of the breastbone) and the other hand on top. Compressions must be delivered hard and fast, pushing down to a depth of at least 2 inches (5 centimeters) but no more than 2.4 inches (6 centimeters) for an average adult. The rate must be maintained between 100 and 120 compressions per minute. Full chest recoil is also important, allowing the chest to fully return to its normal position after each compression so the heart can refill with blood.
A – Establishing a Clear Airway
The “A” step focuses on establishing an open airway after the initial set of compressions. When consciousness is lost, muscles relax, causing the tongue and soft tissues to obstruct the flow of air. This blockage must be corrected before rescue breathing can be effective. The standard technique for opening the airway is the Head Tilt-Chin Lift maneuver.
To perform this maneuver, the rescuer places one hand on the forehead and gently tilts the head back. Simultaneously, the fingertips of the other hand are placed under the chin, and the jaw is lifted forward. This action moves the tongue away from the back of the throat, aligning the airway for air passage. If a spinal injury is suspected, the jaw-thrust maneuver is preferred to avoid moving the neck.
B – Providing Rescue Breathing
Breathing, or “B,” is the final step and involves delivering rescue breaths to supply oxygen to the lungs. After 30 compressions and opening the airway, the rescuer pinches the person’s nose shut while keeping the chin lifted. If available, a barrier device should be used before the rescuer forms a seal over the person’s mouth and delivers two breaths, each lasting approximately one second.
Each rescue breath should cause a visible, gentle rise of the chest. Excessive ventilation must be avoided because it can increase pressure inside the chest, reducing the blood flow returning to the heart. The cycle continues with a ratio of 30 compressions to 2 breaths. For lay rescuers unable to provide ventilations, performing continuous chest compressions alone (hands-only CPR) is recommended, though the full C-A-B sequence remains necessary in cases like drowning or opioid overdose.