🚑 Emergency Care introductory Lesson 5 of 7 4 min read

CPR and Basic Life Support

The Chain of Survival, high-quality chest compressions, the 30:2 compression-to-breath ratio, safe use of an AED, and hands-only CPR, reflecting current resuscitation guidance.

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What you'll learn

  • Describe the links in the Chain of Survival for cardiac arrest.
  • State the recommended adult compression rate and depth for high-quality CPR.
  • Explain the 30:2 compression-to-breath ratio and how to minimize interruptions.
  • Outline the safe steps for using an automated external defibrillator (AED).
  • Explain when hands-only CPR is appropriate.

Overview

Cardiac arrest is the sudden loss of heart function. Blood stops circulating, the brain is starved of oxygen, and without intervention death follows within minutes. CPR (cardiopulmonary resuscitation) and defibrillation can keep blood flowing and restart an effective rhythm. This lesson covers the Chain of Survival, how to perform high-quality compressions, the 30:2 ratio, safe AED use, and hands-only CPR.

Important: This is educational content, not a substitute for certified hands-on CPR training from a program such as the American Heart Association or American Red Cross. Reading this does not certify you to perform CPR. In a real emergency, call your local emergency number immediately and, if an AED is available, send someone to retrieve it.

The Chain of Survival

Survival depends on several actions happening quickly and in order. The Chain of Survival for an adult with sudden cardiac arrest is:

  1. Recognition and activation — recognize the arrest and call for emergency help.
  2. Early CPR — start chest compressions right away.
  3. Rapid defibrillation — use an AED as soon as one is available.
  4. Advanced care — EMS and hospital teams provide medications and further treatment.
  5. Recovery — ongoing care and rehabilitation after resuscitation.

Every link matters; a delay in any one lowers the chance of survival. This is why bystander action in the first minutes is so powerful.

Recognizing Cardiac Arrest

Check an unresponsive person quickly:

  1. Confirm the scene is safe and tap the person, shouting to check for a response.
  2. Look for no breathing or only gasping (agonal breathing is not normal breathing).
  3. If there is no response and no normal breathing, treat it as cardiac arrest, call for help, and get an AED.

High-Quality Chest Compressions

Compressions are the heart of CPR. To perform them on an adult:

  1. Place the heel of one hand on the center of the chest (lower half of the breastbone) and the other hand on top.
  2. Keep your arms straight and shoulders directly over your hands.
  3. Push hard and fast at a rate of 100–120 compressions per minute.
  4. Compress at least about 2 inches (5 cm) deep.
  5. Allow full chest recoil between compressions so the heart refills.
  6. Minimize interruptions — pauses reduce blood flow.
ElementTarget
Rate100–120 per minute
Depth (adult)About 2 inches (5 cm)
RecoilFull, between each push
InterruptionsAs few and brief as possible

Compressions and Breaths: 30:2

A trained rescuer who is willing and able to give rescue breaths uses cycles of 30 compressions followed by 2 breaths. Each breath should be delivered over about one second and make the chest visibly rise. Rescuers use a barrier device or bag-mask to protect themselves. After 2 breaths, immediately resume compressions.

Hands-Only CPR

For an untrained bystander who witnesses an adult suddenly collapse, hands-only CPR — continuous compressions with no breaths — is recommended. It is simpler, avoids hesitation about mouth-to-mouth contact, and keeps blood circulating. Any CPR is far better than none. Hands-only CPR is intended for adults; infants, children, and drowning or breathing-related arrests benefit from breaths, which is another reason full training is valuable.

Using an AED

An automated external defibrillator (AED) analyzes the heart rhythm and, if needed, delivers a shock. AEDs are designed for lay rescuers and give spoken instructions.

  1. Turn the AED on and follow its voice prompts.
  2. Expose and dry the chest, then apply the pads as pictured on them.
  3. Stop compressions and ensure no one is touching the patient while it analyzes.
  4. If a shock is advised, make sure everyone is clear, then press the shock button.
  5. Immediately resume compressions after the shock and continue following prompts.

Continue CPR and AED use until EMS arrives, the patient begins to breathe and move, or you are physically unable to continue.

Clinical Relevance

Bystander CPR and early AED use can roughly double or triple the chance of surviving out-of-hospital cardiac arrest. The reason is time: for every minute without CPR and defibrillation, survival falls sharply. High-quality compressions — the right rate, adequate depth, full recoil, and few interruptions — keep oxygenated blood moving to the brain and heart until a shock or advanced care can restore a normal rhythm. This is why communities place AEDs in public spaces and why learning CPR through a certified course is one of the most valuable skills a person can have.

Going deeper advanced

Extra depth for when you're ready — expanded automatically in Advanced mode.

The physiology behind compressions

Chest compressions generate blood flow by raising pressure inside the chest and by directly squeezing the heart, pushing oxygenated blood toward the brain and coronary arteries. Full recoil is essential because it drops the pressure and lets blood return to fill the heart before the next push, so incomplete recoil quietly starves the circulation. Every pause also lets built-up coronary perfusion pressure collapse, and it takes several compressions to rebuild it, which is why interruptions are minimized.

Chest compression fraction and shockable rhythms

High-quality CPR is often summarized by the chest compression fraction, the proportion of arrest time actually spent compressing; keeping it high (commonly a target above about 60 percent) improves outcomes. Defibrillation only helps certain rhythms: ventricular fibrillation and pulseless ventricular tachycardia are 'shockable' because a shock can reset their chaotic electrical activity, whereas asystole and pulseless electrical activity are 'non-shockable' and are treated with compressions and advanced care rather than a shock. This is why an AED analyzes the rhythm before advising whether to shock.

Key terms

Cardiac arrest
The sudden loss of effective heart function, when the heart stops pumping blood and the person becomes unresponsive and stops breathing normally.
CPR
Cardiopulmonary resuscitation; chest compressions and, when trained, rescue breaths that circulate oxygenated blood during cardiac arrest.
Chain of Survival
The sequence of actions that improves survival from cardiac arrest, from early recognition and CPR to defibrillation and advanced care.
Chest compressions
Rhythmic pushes on the center of the chest that pump blood when the heart cannot.
AED
Automated external defibrillator; a device that analyzes the heart rhythm and can deliver a shock to restore an effective rhythm.
Defibrillation
The delivery of an electrical shock to reset a chaotic heart rhythm such as ventricular fibrillation.
Hands-only CPR
CPR using continuous chest compressions without rescue breaths, recommended for untrained bystanders of an adult in cardiac arrest.
Recoil
Allowing the chest to return fully to its normal position between compressions so the heart can refill.

Check your understanding

6 questions · answers reveal instantly.

  1. 1.What is the recommended compression rate for adult CPR?
  2. 2.How deep should chest compressions be for an average adult?
  3. 3.For a single trained rescuer performing adult CPR with breaths, the compression-to-ventilation ratio is:
  4. 4.When an AED instructs you to deliver a shock, you should first:
  5. 5.Hands-only CPR (compressions without breaths) is most appropriate for:
  6. 6.Allowing full chest recoil between compressions is important because it:

Citations & References

Links open publicly available educational and peer-reviewed sources.

  1. American Heart Association: CPR & First Aid. ↗
  2. American Red Cross: First Aid & CPR. ↗
  3. Centers for Disease Control and Prevention (CDC). ↗