The ABCs represent a universally recognized mnemonic that serves as the foundation for initial patient assessment and treatment in emergency and first aid situations. This established protocol provides a systematic, prioritized sequence for addressing life-threatening issues, ensuring the most immediate physiological needs are met first to sustain life. The framework dictates a step-by-step approach, as the success of each subsequent action depends on the successful completion of the preceding one. Following this sequence helps rescuers quickly identify and manage problems.
Airway Management
The first step in any emergency is establishing a clear path for air to enter the lungs. The tongue is the most frequent obstruction in an unconscious person, often collapsing backward to block the upper airway. Rescuers must quickly assess the patient’s mouth and throat for foreign objects, such as vomit or debris, that might impede airflow.
If an obstruction is suspected, specific manual maneuvers are used. The head tilt/chin lift technique gently moves the jaw forward to lift the tongue away from the back of the throat. If a neck or spinal injury is a concern, the jaw thrust maneuver is employed, which displaces the jaw without manipulating the neck vertebrae. Ensuring the airway is physically open is paramount.
Assessing and Supporting Breathing
Once the airway is secured, the next step is to evaluate respiration. The classic assessment involves the “Look, Listen, and Feel” method, conducted over a period of up to ten seconds. The rescuer looks for chest rise and fall, listens for air moving at the nose and mouth, and feels for airflow on their cheek.
Normal breathing is characterized by a regular rate and adequate depth. If the patient is not breathing or is only gasping—a sign of inadequate respiration—ventilation support must be initiated immediately. This involves providing rescue breaths, delivering oxygen-rich air to the patient’s lungs to ensure the blood can be oxygenated before circulation.
Addressing Circulation and Hemorrhage
The third component involves managing the patient’s blood flow to ensure oxygenated blood reaches vital organs. This is accomplished by rapidly checking for a pulse, typically at the carotid artery in the neck, to confirm cardiac output. However, the immediate priority in many trauma scenarios is controlling massive external hemorrhage before addressing a weak or absent pulse.
Severe bleeding can lead to death within minutes, making its immediate control paramount. Direct pressure should be applied firmly to the wound with a clean cloth or dressing to compress damaged blood vessels and promote clotting. If direct pressure is insufficient or the bleeding is from a limb, a tourniquet may be necessary to completely stop arterial flow to the injury site.
If circulation is absent, as indicated by the lack of a pulse, chest compressions must begin immediately. Cardiopulmonary resuscitation (CPR) involves rhythmic compressions of the chest to manually pump blood from the heart to the brain and other organs. High-quality compressions are delivered to a depth of approximately two to two-and-a-half inches in adults, aiming for a rate of 100 to 120 compressions per minute to maintain minimal blood flow until professional help arrives.
The Evolution of Emergency Sequence
While the traditional ABC sequence provides a logical framework for most medical and trauma emergencies, a significant modification has been adopted for lay rescuers responding to sudden cardiac arrest. This modified approach is known as CAB, prioritizing Circulation over Airway and Breathing. This change was implemented because the primary issue in sudden cardiac arrest is the immediate cessation of blood flow.
The rationale for the CAB sequence is that the patient’s blood still holds enough residual oxygen to sustain the brain for a few minutes. Prioritizing chest compressions immediately delivers this existing oxygen to the vital organs without the delay of opening the airway and giving rescue breaths. This immediate focus on high-quality compressions minimizes the interruption of blood flow, which is the most time-sensitive intervention in these specific scenarios. The shift recognizes that maximizing perfusion is more beneficial than initial ventilation steps in cases of sudden collapse.