The acronym ABC represents a foundational principle in emergency medicine and first aid, standing for Airway, Breathing, and Circulation. This systematic approach is a mnemonic designed to help rescuers prioritize life-saving interventions for an unresponsive person. The sequence focuses on the three most immediate threats to life, as a problem with any one element can lead to rapid deterioration. Addressing the components in this order ensures that oxygen can enter the body and be distributed to the brain and other organs.
Airway Management
The “A” in ABC mandates that the rescuer first ensure the patient has a clear and open airway. This step is a prerequisite for effective breathing and circulation. The most common obstruction in an unconscious person is the tongue, which relaxes and falls backward to block the throat. Other obstructions include foreign bodies, vomit, or blood, which must be managed immediately. To open a blocked airway, first aiders use the head-tilt, chin-lift maneuver. This technique involves tilting the head backward while lifting the chin forward, which mechanically lifts the tongue away from the back of the throat.
Assessing and Supporting Breathing
Once the airway is open, the next step, “B,” is to assess and support the patient’s breathing. Assessment involves the classic “Look, Listen, and Feel” technique, which should take no more than 10 seconds. The rescuer looks for the rise and fall of the chest, listens for breath sounds, and feels for airflow. If the person is not breathing normally or is only gasping, the rescuer must provide rescue breaths. In a combined cardiopulmonary resuscitation (CPR) scenario, this involves delivering two breaths after every 30 chest compressions. To administer a rescue breath, the rescuer seals the mouth and blows steadily for about one second, watching for the chest to visibly rise.
Circulation and Compression
The final component, “C,” traditionally stood for Circulation, referring to the flow of oxygenated blood to the body’s tissues. For an unresponsive, non-breathing person, circulation must be supported externally through chest compressions. These compressions manually squeeze the heart, pumping blood to the brain and coronary arteries. To perform effective compressions, the rescuer places the heel of one hand in the center of the chest, placing the other hand on top. Compressions must be delivered at a rate of 100 to 120 times per minute. The recommended depth for an adult is at least 2 inches (5 cm), ensuring full chest recoil after each compression to allow the heart to refill.
The Evolution of Emergency Protocols
While ABC remains the standard priority sequence for general first aid and trauma, the protocol for treating sudden cardiac arrest in adults has shifted. Major health organizations now recommend a CAB sequence: Circulation, Airway, and Breathing. This change was officially adopted in 2010. The rationale is that in the first few minutes after the heart stops, the patient’s blood still contains usable oxygen. Starting with chest compressions (C) immediately provides this oxygen-rich blood to the brain and heart, which is the most time-sensitive requirement. Beginning with compressions minimizes the delay caused by attempting to open the airway and deliver initial breaths. Studies show the CAB sequence allows compressions to be initiated sooner, improving the chances of survival.