C-A-B is a memory aid for the first core actions in CPR: Compressions, Airway, and Breathing. It matters because an unresponsive person who is not breathing normally may have only minutes before the brain and heart are damaged by lack of blood flow. Starting with chest compressions helps move oxygen-rich blood that is already in the lungs and bloodstream.
This order is used for an unresponsive adult or child when CPR is needed, while also calling emergency services and getting an AED if available.
The C step means giving 30 chest compressions in the center of the chest at a steady, fast rate. The A step means opening the airway by tilting the head back and lifting the chin, unless a spinal injury is suspected and trained care is available. The B step means giving 2 rescue breaths that make the chest rise, then returning immediately to compressions.
The cycle repeats as 30 compressions and 2 breaths until help arrives, an AED is ready, the person responds, or the rescuer is too exhausted to continue.
Understanding Health: Order of CPR steps (C-A-B)
CPR works by taking over part of the job of the heart. Each downward push squeezes the heart between the breastbone and spine. This creates a small but important flow of blood to the brain, heart, and other organs.
The chest must fully rise after every push so the heart can refill with blood. Leaning on the chest between compressions reduces this refill. Good compressions are tiring because they need enough depth and a regular rhythm.
For an adult, the chest is pushed down at least two inches. For a child, the target is about one third of the chest depth. For an infant, rescuers use a different hand position and gentler force.
Breathing can look confusing during a real emergency. A person in cardiac arrest may make occasional gasps, snorts, or irregular breaths. These are called agonal breaths.
They are not normal breathing and do not mean the person is recovering. A responder should quickly check for responsiveness and normal breathing, then act without long delays. Time spent searching for a pulse can delay care, especially for an untrained bystander.
CPR classes teach people how to assess the situation safely. The scene matters too. A rescuer should not enter traffic, fire, deep water, or another dangerous area without help.
Rescue breaths add oxygen, but the airway must be open and the breaths must be controlled. Blowing too hard or too long can force air into the stomach. This may cause vomiting and makes CPR harder.
A visible chest rise shows that air is entering the lungs. If the chest does not rise, the rescuer reopens the airway and tries again. Something blocking the mouth may need to be removed only if it can be clearly seen.
Blind finger sweeps can push an object farther in. If a person has a known choking emergency and becomes unresponsive, CPR still includes checking the mouth for a visible object between cycles.
An AED is a key part of modern CPR because some cardiac arrests are caused by an abnormal heart rhythm that needs an electric shock. The device gives spoken instructions and checks the rhythm through sticky pads on the chest. A rescuer should turn it on as soon as it arrives, expose and dry the chest if needed, attach the pads as shown, and keep everyone clear during analysis or a shock.
The AED does not replace compressions. CPR continues whenever the device is not analyzing or delivering a shock. Students should learn that real emergencies are stressful.
Clear roles help. One person calls emergency services, one begins care, and another finds the AED when other people are present. Formal training gives practice with body position, pressure, breaths, infant care, and emergency decisions.
Key Facts
- C-A-B = Compressions, Airway, Breathing.
- Compression-to-breath ratio for one rescuer adult or child CPR = 30:2.
- C = 30 chest compressions before opening the airway.
- A = head tilt and chin lift to open the airway.
- B = 2 rescue breaths, each about 1 second, with visible chest rise.
- Adult compression rate = 100 to 120 compressions per minute.
Vocabulary
- CPR
- CPR is an emergency procedure that uses chest compressions and rescue breaths to help circulate blood and oxygen when a person is not breathing normally.
- Compressions
- Compressions are firm pushes on the center of the chest that help move blood to the brain, heart, and other organs.
- Airway
- The airway is the path air follows from the mouth and nose to the lungs.
- Rescue breaths
- Rescue breaths are breaths given into a person's mouth or a barrier device to help move air into the lungs.
- AED
- An AED is an automated external defibrillator that can analyze heart rhythm and deliver a shock if needed.
Common Mistakes to Avoid
- Starting with A-B-C instead of C-A-B: this delays compressions, which are needed right away to circulate oxygenated blood already in the body.
- Pressing too slowly or pausing too often: weak or interrupted compressions reduce blood flow to the brain and heart.
- Giving breaths before opening the airway: air may not reach the lungs if the tongue or soft tissue is blocking the airway.
- Blowing too hard or too long during rescue breaths: excessive air can enter the stomach and may reduce the quality of CPR.
Practice Questions
- 1 A rescuer completes 4 full CPR cycles using the 30:2 ratio. How many chest compressions and how many rescue breaths are given?
- 2 At a compression rate of 110 compressions per minute, about how many seconds should 30 compressions take?
- 3 A student says the rescuer should open the airway first because breathing is the main problem. Explain why the C-A-B order starts with compressions instead.