CPR: The Life-Saving Skill That Can Bring Hope Back When the Heart Stops

The Correct Option Is C : CPR

A Complete Guide to Cardiopulmonary Resuscitation, Emergency Response, and the Science of Saving a Life

Introduction: When Every Second Matters

Imagine a person suddenly collapsing in a busy market, a classroom, a hospital corridor, or at home. They do not respond when someone calls their name. Their breathing is absent or abnormal. People gather around, frightened and uncertain about what to do. Some shout for help, while others reach for their phones. Every second passes, and the person's brain and vital organs are receiving little or no oxygen-rich blood.

In such a moment, one simple but powerful intervention can make a life-changing difference: cardiopulmonary resuscitation, commonly known as CPR.

CPR is an emergency procedure used when a person's heart stops pumping blood effectively. It combines chest compressions, and when appropriate, rescue breaths to maintain circulation and oxygen delivery until the heart's rhythm can be restored or advanced medical care becomes available.

Cardiac arrest can occur in hospitals, homes, workplaces, sports facilities, schools, and public places. It may affect people with known heart disease, but it can also occur unexpectedly in someone who appeared healthy moments earlier. Children and infants can also experience cardiac arrest, although the causes often differ from those in adults.

The tragedy of cardiac arrest is that it can progress rapidly, but the opportunity to help may be right beside the victim. A bystander who recognizes the emergency, calls for assistance, begins CPR, and uses an automated external defibrillator (AED) when available can become an essential part of the chain of survival.

CPR does not guarantee survival, and it does not replace professional medical treatment. However, prompt, high-quality CPR can maintain some blood flow to the brain and heart while emergency responders work to restore circulation.

This article explores CPR from the ground up: its definition, physiology, indications, recognition of cardiac arrest, adult CPR technique, child and infant differences, rescue breathing, AED use, advanced life support, complications, post-cardiac arrest care, and common misconceptions. It also provides practical revision tables for medical and nursing students.

Important safety note: This article is for education and first-aid awareness. In a real emergency, call your local emergency number, follow the emergency dispatcher’s instructions, and use the CPR method appropriate to the person's age and circumstances. Practical training with a qualified CPR instructor is strongly recommended.

1. What Is CPR?

Cardiopulmonary resuscitation is an emergency technique intended to maintain circulation and, when indicated, breathing in a person experiencing cardiac arrest.

The term contains three important elements:

Cardio: Related to the heart.
Pulmonary: Related to the lungs.
Resuscitation: An attempt to restore or support vital functions.

During cardiac arrest, the heart may stop beating effectively or develop an electrical rhythm that produces no meaningful circulation. As a result, blood flow to the brain, heart muscle, kidneys, and other organs falls dramatically or stops.

Chest compressions mechanically press the heart and surrounding structures, helping move blood through the circulation. Rescue breaths provide oxygen to the lungs when ventilation is needed. Defibrillation can terminate certain dangerous heart rhythms and allow the heart's normal electrical activity to resume.

CPR is therefore best understood as a bridge to definitive treatment, rather than a complete cure for cardiac arrest.

Main objectives of CPR

The principal objectives are to:

Maintain blood flow to the brain and other vital organs.
Deliver oxygen to tissues as effectively as possible.
Increase the chance that defibrillation will succeed when a shockable rhythm is present.
Reduce the duration of complete circulatory interruption.
Support the person until spontaneous circulation returns or professional resuscitation decisions are made.

High-quality CPR emphasizes effective chest compressions, minimal interruptions, appropriate ventilation, and early use of an AED.

2. Understanding Cardiac Arrest

To understand CPR, it is important to distinguish cardiac arrest from other emergencies that may appear similar.

What is cardiac arrest?

Cardiac arrest occurs when the heart suddenly stops generating effective circulation. The person usually becomes unresponsive and stops breathing normally or develops abnormal gasping.

Without prompt intervention, oxygen delivery to the brain and other organs becomes critically inadequate.

Cardiac arrest versus heart attack

These conditions are related but are not the same.

A heart attack, also called myocardial infarction, occurs when blood flow to part of the heart muscle is severely reduced or blocked, causing injury to the muscle. A cardiac arrest occurs when the heart can no longer maintain effective circulation.

A heart attack can trigger cardiac arrest, but many heart attacks do not immediately cause cardiac arrest. Conversely, cardiac arrest can result from electrical disorders, severe respiratory problems, drowning, major blood loss, poisoning, and other conditions.

Feature	Heart attack	Cardiac arrest
Main problem	Reduced blood supply to heart muscle	Failure of effective circulation
Person's condition	Often conscious initially	Usually suddenly unresponsive
Breathing	Often present	Absent or abnormal
Pulse	Usually present initially	No effective pulse in cardiac arrest
Immediate priority	Emergency medical evaluation	Immediate CPR, emergency activation, and AED when indicated

A person having a heart attack may complain of chest pressure, sweating, breathlessness, nausea, or discomfort spreading to the arm, back, neck, or jaw. If the person collapses and becomes unresponsive with absent or abnormal breathing, the response must shift immediately to suspected cardiac arrest.

Other conditions that may resemble cardiac arrest

Fainting, seizures, severe hypoglycemia, stroke, and some respiratory emergencies can cause collapse or altered consciousness. However, a lay rescuer should not delay CPR when a person is unresponsive and is not breathing normally.

If the person is unresponsive and only gasping, treat the situation as possible cardiac arrest. Gasping is not normal breathing.

3. Why Is CPR So Important?

The brain requires a continuous supply of oxygen and glucose to maintain normal function. When circulation stops, oxygen delivery rapidly declines. Brain injury can begin within minutes, although the exact timeline depends on factors such as the cause of arrest, temperature, prior oxygen levels, and the speed of treatment.

The heart muscle also requires oxygen. During cardiac arrest, reduced coronary blood flow can make successful restoration of a normal rhythm more difficult.

CPR helps by generating partial blood flow.

The role of chest compressions

Each chest compression creates pressure within the chest and helps move blood toward the brain and other organs. When the rescuer releases pressure, the chest recoils, allowing blood to return to the heart.

This is why both compression and complete recoil matter.

Leaning continuously on the chest between compressions prevents full recoil and can reduce the effectiveness of CPR.

The role of rescue breaths

Rescue breaths move air into the lungs, supporting oxygen delivery. They are especially important in many cases of pediatric cardiac arrest and in emergencies caused by drowning, suffocation, or other respiratory problems.

In sudden adult cardiac arrest, immediately starting chest compressions is crucial. If a bystander is untrained or unwilling to provide rescue breaths, hands-only CPR is preferable to doing nothing.

Why early defibrillation matters

Some cardiac arrests are caused by ventricular fibrillation or pulseless ventricular tachycardia. These rhythms produce little or no effective circulation but may respond to an electrical shock.

An AED analyzes the rhythm and advises whether a shock is appropriate. CPR helps preserve circulation while the AED is obtained and prepared.

CPR and defibrillation are complementary interventions. Neither should unnecessarily delay the other.

4. The Physiology Behind CPR

The physiological principles of CPR are particularly important for medical, nursing, and paramedic students.

Cerebral perfusion

The brain is highly sensitive to interrupted blood flow. Chest compressions create limited circulation, helping deliver oxygen and glucose to brain tissue.

Although CPR does not usually produce normal cerebral blood flow, it can support the brain while the underlying problem is treated.

Coronary perfusion

The heart requires blood flow through the coronary arteries to recover from cardiac arrest. Effective compressions help generate coronary perfusion pressure.

Repeated interruptions reduce the pressure created by compressions. After an interruption, several compressions may be needed to rebuild effective perfusion.

For this reason, unnecessary pauses should be avoided.

Oxygen delivery

Oxygen delivery depends on both blood flow and the oxygen content of blood. Chest compressions support circulation, while ventilation helps maintain oxygen levels when needed.

Excessive ventilation can increase pressure inside the chest, impair venous return to the heart, and reduce blood flow generated by compressions. Rescue breaths should therefore be effective but not excessive.

Chest recoil

Complete recoil allows the chest to return to its resting position between compressions. This promotes venous return and supports the next compression.

A rescuer should release pressure fully after every compression without lifting the hands completely away from the chest.

Why quality matters more than appearance

CPR should not be judged by how dramatic or forceful it looks. The goal is to provide compressions at the recommended rate and depth, permit recoil, and minimize pauses.

Excessively shallow compressions may generate insufficient circulation. Excessively deep compressions can increase the risk of injury. A consistent, controlled technique is essential.

5. When Should CPR Be Started?

CPR is indicated when a person is unresponsive and is not breathing normally, or is only gasping, suggesting cardiac arrest.

Important signs of cardiac arrest

Look for the following:

Sudden collapse.
No response to shouting or gentle tapping.
No normal breathing.
Occasional gasping, snorting, or irregular breathing that is not normal.
In healthcare settings, absence of a definite pulse when assessed promptly by a trained professional.

For a lay rescuer, checking for a pulse is not recommended because it can be difficult and may delay treatment.

How long should you assess the person?

The initial assessment should be rapid. If the person is unresponsive and not breathing normally, activate emergency help and start CPR.

Healthcare professionals trained to check a pulse should generally complete the check within 10 seconds. If they cannot confidently identify a pulse, they should begin CPR according to the relevant resuscitation algorithm.

Do not spend prolonged periods trying to determine whether the person is breathing or has a pulse.

What about agonal gasping?

Agonal gasps are abnormal, irregular breaths that may occur shortly after cardiac arrest. They can sound like snoring, snorting, or labored gasping.

They do not indicate adequate breathing.

An unresponsive person who is only gasping should be treated as being in cardiac arrest.

What if the person is unconscious but breathing normally?

If the person is unresponsive but breathing normally, CPR may not be required immediately. Call emergency services, monitor breathing continuously, and follow dispatcher instructions.

If there is no suspicion of major trauma and it is safe to do so, place the person in the recovery position to help maintain an open airway. If the person stops breathing normally, reposition them on their back and begin CPR.

A person who has collapsed after trauma may require special handling, but airway and breathing emergencies remain priorities.

6. The Chain of Survival

The chain of survival describes the coordinated actions that improve outcomes after cardiac arrest. The 2025 American Heart Association guidelines emphasize a universal chain of survival for adult and pediatric cardiac arrest occurring inside or outside hospitals. citeturn837286search3

The main links include:

1. Recognize the emergency and activate help

Rapid recognition prevents avoidable delays. Someone should call the local emergency number and provide the location, the person's condition, and any relevant information.

2. Start high-quality CPR

Chest compressions should begin promptly when cardiac arrest is suspected. If trained and able, the rescuer should provide rescue breaths as appropriate.

3. Defibrillate early when indicated

An AED should be brought to the scene as soon as possible. If a shock is advised, follow the device's instructions and resume CPR immediately afterward.

4. Provide advanced resuscitation

Emergency medical professionals may provide airway support, oxygen, cardiac monitoring, defibrillation, vascular access, medications, and treatment of reversible causes.

5. Deliver post-cardiac arrest care

A person whose circulation returns may still have serious heart, brain, lung, or metabolic problems. Hospital treatment aims to stabilize organ function, identify the cause, and prevent further injury.

6. Support recovery and follow-up

Recovery may involve rehabilitation, psychological support, neurological assessment, cardiac evaluation, and assistance for family members.

The chain of survival works best when each link is activated quickly and connected to the next.

7. How to Perform Adult CPR: Step-by-Step

The following approach is based on widely used adult basic life support principles. It is an educational summary, not a substitute for practical certification.

Step 1: Check the scene for safety

Before approaching the person, look for hazards such as:

Traffic.
Fire or smoke.
Electrical wires.
Exposed electrical equipment.
Dangerous chemicals.
Unstable structures.
Water hazards.
Violence or other ongoing threats.

Do not become another casualty. If the area is unsafe, do not enter until it is safe or trained responders can assist.

Use gloves or other protective equipment if immediately available, but do not delay essential CPR while searching for equipment.

Step 2: Check responsiveness

Approach the person and shout loudly, “Are you okay?”

If there is no response, gently tap the shoulders. Do not shake the person aggressively, particularly if a neck or spinal injury is possible.

If the person does not respond and is not breathing normally, assume cardiac arrest may be present.

Step 3: Call emergency services

Activate the local emergency response system immediately.

If another person is present, give clear instructions:

“You, call emergency services.”
“You, bring the AED.”
“You, guide the ambulance to this location.”

Assigning tasks directly is better than shouting general requests such as “Somebody help!”

If you are alone with a mobile phone, use the speaker function if possible so you can follow the dispatcher’s instructions while starting CPR.

The appropriate emergency number varies by country and locality. Know the number and emergency response arrangements where you live or work.

Step 4: Position the person

Place the person on their back on a firm, flat surface whenever possible.

A mattress or soft surface can reduce compression effectiveness. If the person is on a bed, follow dispatcher guidance and make the best safe arrangement available.

Expose the chest sufficiently to locate the correct hand position and use an AED.

Step 5: Position your hands

For an adult, place the heel of one hand in the center of the chest, on the lower half of the breastbone, also called the sternum.

Place the heel of your other hand on top. Interlock your fingers or keep them lifted away from the ribs.

Position your shoulders directly over your hands and keep your arms straight.

Step 6: Give chest compressions

Compress the chest firmly and rhythmically.

For adults, the standard targets are:

Rate: 100–120 compressions per minute.
Depth: At least 5 cm (2 inches), while avoiding excessive depth beyond approximately 6 cm (2.4 inches) in an average adult.
Recoil: Allow the chest to return fully after every compression.
Interruptions: Keep pauses as short as possible.

Push hard and fast, but maintain control. Let your upper body provide the downward force rather than relying only on your arm muscles.

A consistent rhythm helps. A familiar song with a beat in the recommended range may help maintain pace during practice, but real-world performance should prioritize the recommended compression rate.

Step 7: Give rescue breaths if trained and able

For an adult, a trained rescuer who can provide breaths should generally use a ratio of 30 chest compressions to 2 rescue breaths when no advanced airway is in place.

After 30 compressions:

Open the airway using the head-tilt/chin-lift maneuver, unless a specific trauma situation requires a modified approach under trained guidance.
Pinch the nose closed.
Make a seal over the person's mouth.
Give one breath lasting about one second, watching for visible chest rise.
Give a second breath in the same way.
Resume chest compressions promptly.

Avoid delivering breaths too forcefully or too rapidly. Excessive ventilation can impair circulation and increase the risk of air entering the stomach.

If the chest does not rise, reposition the airway and try again, without creating a prolonged interruption in compressions.

Step 8: If you cannot provide rescue breaths

If you are untrained, unable to provide breaths, or unwilling to give mouth-to-mouth ventilation, perform hands-only CPR for a collapsed adult with suspected sudden cardiac arrest.

Call emergency services and push hard and fast in the center of the chest, at 100–120 compressions per minute. Follow dispatcher instructions.

Hands-only CPR is much better than doing nothing.

Step 9: Use an AED as soon as it arrives

Turn on the AED and follow its voice or visual prompts.

Attach the pads to the bare chest as shown in the diagrams. Ensure that no one touches the person during rhythm analysis or a shock.

If the AED advises a shock, make sure everyone is clear and deliver the shock as instructed. Resume CPR immediately afterward, beginning with chest compressions.

If no shock is advised, resume CPR immediately when directed.

Step 10: Continue until help takes over or the person shows signs of life

Continue CPR, switching compressors about every two minutes if another trained rescuer is available, or sooner if fatigue makes compressions less effective.

Stop compressions only when:

The person shows clear signs of life and begins breathing normally.
Trained emergency personnel take over.
The scene becomes unsafe.
You are physically unable to continue.
The AED or emergency dispatcher instructs you to pause for a specific reason.

If the person begins moving or breathing normally, reassess carefully. Abnormal gasping alone is not a reason to stop CPR.

8. Adult CPR: Quick Reference Table

Component	Standard adult target
Responsiveness check	Brief, rapid assessment
Emergency activation	As soon as cardiac arrest is suspected
Compression position	Center of chest, lower half of sternum
Compression rate	100–120/min
Compression depth	5–6 cm approximately
Chest recoil	Complete recoil after every compression
Compression-to-breath ratio	30:2 when providing breaths without an advanced airway
Rescue breath duration	About 1 second each, enough for visible chest rise
AED use	As soon as available
Rhythm analysis or shock	Keep everyone clear of the patient
After a shock	Resume CPR immediately as directed

These are standard adult basic life support targets. Clinical protocols and the needs of individual patients may require additional considerations.

9. Hands-Only CPR: A Vital Skill for the Public

Many people hesitate to perform CPR because they fear doing something wrong, are unsure about rescue breathing, or worry about mouth-to-mouth contact.

Hands-only CPR offers a simple response for a bystander witnessing a sudden collapse in an adult.

How to perform hands-only CPR

Check whether the scene is safe.
Check responsiveness.
If the person is unresponsive and not breathing normally, call emergency services or direct someone else to call.
Ask someone to bring an AED.
Place the heel of one hand in the center of the chest and the other hand on top.
Push hard and fast at 100–120 compressions per minute.
Allow full chest recoil and avoid unnecessary pauses.
Follow the AED's instructions when it arrives.

Who benefits from hands-only CPR?

Hands-only CPR is especially useful for bystanders responding to sudden adult cardiac arrest.

However, rescue breaths are particularly important in many arrests involving infants, children, drowning, suffocation, and respiratory causes. In these situations, a trained rescuer should provide CPR with breaths when able.

The key message is simple: Do not let fear or uncertainty prevent you from calling for help and beginning appropriate CPR.

10. Rescue Breathing and Airway Management

Ventilation is an important component of CPR, especially when cardiac arrest follows a respiratory emergency.

Head-tilt/chin-lift maneuver

For a person without suspected major trauma, the head-tilt/chin-lift maneuver helps open the airway.

Place one hand on the forehead and gently tilt the head backward. Place the fingertips of the other hand under the bony part of the chin and lift upward.

Avoid pressing deeply into the soft tissues beneath the chin, as this can obstruct the airway.

Mouth-to-mouth ventilation

If trained and willing to provide mouth-to-mouth breaths:

Open the airway.
Pinch the nose closed.
Seal your mouth over the person's mouth.
Give a breath lasting about one second.
Watch for chest rise.
Give the second breath.
Return immediately to compressions.

A pocket mask or bag-mask device may be used by trained rescuers when available.

Why excessive ventilation is harmful

Giving too many breaths or blowing too forcefully increases intrathoracic pressure. This may reduce blood returning to the heart, decrease cardiac output during CPR, and increase the likelihood of gastric inflation.

The objective is not to fill the lungs as forcefully as possible. It is to provide enough air to produce visible chest rise while minimizing interruptions.

Airway obstruction during CPR

If the chest does not rise despite correct technique, reconsider airway position and look for an obstruction if it can be safely identified.

Do not perform blind finger sweeps in the mouth. A blind sweep may push an object deeper into the airway.

11. CPR for Children

Pediatric resuscitation differs from adult CPR because cardiac arrest in children is more frequently associated with respiratory failure, airway obstruction, drowning, or shock than with a primary cardiac rhythm problem.

Early ventilation can therefore be especially important.

A child is generally considered to be from one year of age until puberty for basic life support purposes. Local training protocols may specify additional details.

Recognizing pediatric cardiac arrest

Possible signs include:

Unresponsiveness.
Absence of normal breathing or gasping.
Sudden collapse.
Poor muscle tone.
A preceding episode of respiratory distress or severe illness.

A lay rescuer should not delay CPR to check a pulse.

Child CPR technique

Ensure the scene is safe.
Check responsiveness and breathing rapidly.
Call emergency services and obtain an AED.
Place the child on their back on a firm, flat surface.
Position one or two hands on the lower half of the sternum, depending on the child's size.
Compress at 100–120 per minute.
Compress to approximately one-third of the chest's front-to-back diameter, generally about 5 cm in a child.
Allow complete recoil.
If trained, give rescue breaths using the appropriate compression-to-breath ratio.
Continue until the child recovers, help takes over, or you cannot continue.

Compression-to-breath ratio

For pediatric CPR without an advanced airway:

A lone rescuer generally uses 30 compressions followed by 2 breaths.
Two trained rescuers generally use 15 compressions followed by 2 breaths.

Follow the current local pediatric resuscitation protocol and dispatcher instructions.

When should a lone rescuer call for help?

If a lone rescuer witnesses a sudden collapse, emergency activation and obtaining an AED should occur promptly.

For a child or infant whose collapse was not witnessed and may be caused by a respiratory problem, some pediatric algorithms recommend giving about two minutes of CPR before leaving briefly to activate emergency services if no phone is available. If a phone is available, use speaker mode and follow the dispatcher’s instructions.

Because these situations differ, formal training is especially valuable.

12. CPR for Infants

An infant is generally defined as a child younger than one year, excluding newborns requiring immediate birth resuscitation.

Infant CPR requires a gentler, age-appropriate technique because the chest is smaller and more delicate.

Recognizing infant cardiac arrest

Warning signs include:

No response to stimulation.
No normal breathing.
Gasping or irregular breaths.
Sudden limpness.
Severe respiratory distress followed by unresponsiveness.

Do not shake an infant to assess responsiveness. Gently tap the foot or use another appropriate stimulus.

Infant CPR technique

Place the infant on their back on a firm, flat surface.
Check responsiveness and breathing rapidly.
Call emergency services and obtain an AED.
Position the heel of one hand, or use the two-thumb encircling-hands technique when trained and appropriate, on the lower half of the sternum.
Compress at 100–120 per minute.
Compress approximately one-third of the chest's front-to-back diameter, about 4 cm in an average infant.
Allow full recoil after each compression.
Provide rescue breaths if trained, using an appropriately gentle technique.
Continue CPR and follow emergency guidance.

The 2025 AHA guidance specifies the heel of one hand or the two-thumb technique for infant compressions, eliminating the two-finger technique from its recommended infant compression methods. citeturn837286search3

Infant rescue breaths

Because an infant's mouth and nose are small, a trained rescuer may cover both the mouth and nose with their mouth to provide gentle breaths.

Give enough air to produce visible chest rise. Avoid forceful ventilation.

Important infant safety points

Never use adult compression depth on an infant.
Do not compress the abdomen.
Do not use abdominal thrusts to treat choking in an infant.
Follow infant-specific choking and resuscitation guidance.
Use an AED with pediatric pads or an appropriate pediatric setting when available, without delaying necessary resuscitation.

13. Newborn Resuscitation Is Different

Resuscitation immediately after birth is a specialized process and should not be confused with routine infant CPR.

A newborn who fails to establish effective breathing after delivery may require thermal support, airway positioning, stimulation, assisted ventilation, and other interventions based on heart rate and clinical response.

For many newborns, effective ventilation is the most important initial intervention. Chest compressions are introduced when indicated by the neonatal resuscitation algorithm, generally when the heart rate remains severely low despite effective ventilation.

Neonatal resuscitation requires specific training and equipment. Adult CPR instructions should not simply be applied to a newborn immediately after birth.

14. Automated External Defibrillator (AED)

An automated external defibrillator is a portable device that analyzes a person's heart rhythm and advises whether an electrical shock is needed.

AEDs are designed so that trained and untrained bystanders can use them with the help of voice prompts and diagrams.

Why is an AED important?

Some cardiac arrest rhythms, particularly ventricular fibrillation and pulseless ventricular tachycardia, may be treated with defibrillation.

An AED does not shock every person in cardiac arrest. It analyzes the rhythm and advises a shock only when indicated.

The earlier a shock is delivered for a shockable rhythm, the better the chance of successful resuscitation.

Steps for using an AED

Step 1: Turn on the device.

Open the AED case and press the power button or follow the device's instructions.

Step 2: Expose the chest.

Remove clothing as necessary so the pads can adhere to bare skin. Dry a wet chest quickly when required for pad adhesion and safety.

Step 3: Attach the pads.

Place the pads in the positions shown on their diagrams, commonly one on the upper right chest and the other on the left side of the chest below the armpit.

For infants and small children, use pediatric pads or a pediatric mode if available. If pediatric equipment is unavailable, follow the AED manufacturer's instructions and emergency dispatcher guidance.

Step 4: Allow rhythm analysis.

Make sure nobody touches the person while the AED analyzes the rhythm.

Step 5: Deliver a shock if advised.

Clearly announce that everyone must stand clear. Visually confirm that nobody is touching the person before pressing the shock button if the device requires it.

Step 6: Resume CPR.

Immediately resume CPR when directed by the AED. Do not delay compressions to repeatedly check for a pulse unless the person shows clear signs of life or the device instructs otherwise.

Special AED precautions

Do not use the device in a manner that exposes rescuers to electrical danger.
Keep everyone clear during rhythm analysis and shock delivery.
Avoid placing pads directly over implanted devices when an alternative position is practical.
Follow manufacturer instructions for medication patches and other chest-related issues.
Do not delay CPR while searching extensively for an AED.

An AED is designed to assist resuscitation, not replace chest compressions.

15. Advanced Cardiopulmonary Resuscitation

Basic life support is the foundation of resuscitation. Advanced life support builds on it with trained clinical personnel, monitoring equipment, airway interventions, medications, and treatment of reversible causes.

Advanced interventions should be performed by qualified professionals following current resuscitation protocols.

Cardiac rhythm assessment

Clinical teams use a cardiac monitor or defibrillator to identify the rhythm during cardiac arrest.

The two broad categories are:

Shockable rhythms

Ventricular fibrillation (VF).
Pulseless ventricular tachycardia (pVT).

Non-shockable rhythms

Asystole.
Pulseless electrical activity (PEA).

This distinction is crucial because the treatment pathway differs.

Ventricular fibrillation

Ventricular fibrillation is chaotic electrical activity in which the ventricles fail to contract effectively. It produces no meaningful circulation.

Defibrillation is the key rhythm-specific treatment, alongside high-quality CPR and advanced care.

Pulseless ventricular tachycardia

Pulseless ventricular tachycardia is a rapid ventricular rhythm without an effective pulse. It is managed as a shockable cardiac arrest rhythm.

Asystole

Asystole represents the absence of detectable ventricular electrical activity. It is not treated with defibrillation simply because the patient is in cardiac arrest.

The clinical team provides CPR, appropriate medications, and a search for reversible causes while confirming that the apparent asystole is not due to a technical problem.

Pulseless electrical activity

In PEA, electrical activity may be visible on the monitor, but it does not produce an effective pulse.

The treatment includes CPR, appropriate advanced life support, and prompt identification and treatment of the underlying cause. Defibrillation is not indicated solely because the patient has PEA.

Airway support

Depending on the clinical situation and the team's expertise, airway support may include a bag-mask device, supraglottic airway, or endotracheal intubation.

Airway procedures should not create prolonged interruptions in chest compressions.

Vascular access and medications

Advanced life support may involve intravenous or intraosseous access and medications according to the relevant algorithm.

Medication selection, doses, timing, and routes depend on the rhythm, patient characteristics, cause of arrest, and current protocol. They should not be improvised by untrained bystanders.

End-tidal carbon dioxide monitoring

In clinical settings, waveform capnography can help assess ventilation, confirm placement of an advanced airway, and provide information about CPR quality.

A sudden increase in end-tidal carbon dioxide may suggest return of spontaneous circulation, although clinical assessment and the complete resuscitation context remain important.

16. Reversible Causes of Cardiac Arrest

Advanced resuscitation teams actively look for potentially reversible causes. A commonly taught framework is the Hs and Ts.

The Hs

1. Hypovolemia

Severe loss of circulating blood or fluid can prevent the heart from filling adequately. Causes include major hemorrhage, severe dehydration, and fluid loss.

2. Hypoxia

Insufficient oxygen may result from airway obstruction, respiratory failure, drowning, or other conditions.

3. Hydrogen ion excess (acidosis)

Severe metabolic or respiratory acidosis may contribute to cardiovascular instability.

4. Hypokalemia or hyperkalemia

Abnormal potassium concentrations can disrupt cardiac electrical activity. Both low and high potassium levels may cause dangerous arrhythmias.

5. Hypothermia

Severe lowering of body temperature can impair cardiac function and contribute to arrest.

Other clinical protocols may include additional metabolic or physiological factors in this framework.

The Ts

1. Tension pneumothorax

Air under pressure in the pleural space can compress the lungs and major vessels, reducing venous return.

2. Cardiac tamponade

Fluid or blood around the heart may prevent adequate filling.

3. Toxins

Drug overdose, poisoning, and toxic exposures can trigger respiratory failure, arrhythmias, or circulatory collapse.

4. Pulmonary thrombosis

A large pulmonary embolism can obstruct blood flow through the lungs and cause sudden cardiovascular collapse.

5. Coronary thrombosis

Acute blockage of a coronary artery can cause myocardial infarction and trigger a life-threatening rhythm.

The Hs and Ts are a clinical reasoning aid. They help professionals investigate why cardiac arrest occurred and identify treatments beyond CPR alone.

17. CPR in Special Circumstances

Not every cardiac arrest occurs under the same conditions. The basic priority remains rapid recognition and effective resuscitation, but some situations require additional precautions.

Drowning

Drowning-related cardiac arrest is commonly associated with oxygen deprivation. Rescue breaths are therefore particularly important when a trained rescuer can provide them.

Rescuers should not enter dangerous water unless appropriately trained and equipped. Once the person is safely removed, follow emergency instructions and begin resuscitation when indicated.

Suspected opioid overdose

Opioids can suppress breathing and lead to cardiac arrest.

If an opioid overdose is suspected, activate emergency services, provide CPR and rescue breathing as appropriate, and administer naloxone if it is available and the rescuer knows how to use it.

Naloxone does not replace CPR or emergency evaluation. Continue resuscitation and follow dispatcher instructions.

Electrical injury

Ensure the electrical source has been disconnected before touching the person. If the person is unresponsive and not breathing normally once the scene is safe, begin CPR and use an AED as appropriate.

Severe trauma and bleeding

Major blood loss can cause cardiac arrest. In addition to CPR when indicated, trained responders may need to control catastrophic bleeding and treat the underlying injury.

Do not move a seriously injured person unnecessarily, but do not delay lifesaving airway or resuscitation actions.

Pregnancy

Cardiac arrest during pregnancy requires immediate high-quality CPR and rapid activation of an experienced resuscitation team.

Clinical teams may need to modify positioning, manage the airway early, and consider pregnancy-specific interventions. These are specialized procedures requiring training and current protocols.

Hypothermia

Severe hypothermia can cause cardiac arrest and may require prolonged resuscitation and specialized rewarming. Follow emergency medical guidance and avoid unnecessary rough handling.

Implanted cardiac devices

People with pacemakers or implantable cardioverter-defibrillators may still experience cardiac arrest. CPR should not be withheld because a device is present. AED pads should be positioned according to device and AED guidance.

18. CPR Complications and Safety

CPR can cause injury, particularly when effective compressions are delivered. Possible complications include rib fractures, sternum fractures, bruising, and, less commonly, internal injuries.

These risks must be understood in context: when a person is in cardiac arrest, the immediate danger from untreated loss of circulation is far greater.

Rib fractures

Chest compressions place mechanical stress on the ribs. Fractures can occur even when the rescuer uses appropriate technique.

The possibility of injury should not prevent a bystander from providing indicated CPR.

Gastric inflation

Excessive rescue breaths can force air into the stomach. This may cause abdominal distension, regurgitation, and an increased risk of aspiration.

Give controlled breaths lasting about one second and look for visible chest rise.

Rescuer fatigue

Compressions become less effective as the rescuer tires.

If possible, switch compressors approximately every two minutes. Make the exchange quickly so that interruptions remain minimal.

Infection concerns

The risk of infection during rescue breathing is generally low but is not zero. Barrier devices can reduce direct contact. If a bystander cannot or will not provide rescue breaths, hands-only CPR is preferable to inaction for suspected sudden adult cardiac arrest.

Psychological stress

Witnessing a cardiac arrest can be distressing, even when resuscitation is successful. Bystanders may experience anxiety, guilt, intrusive memories, or uncertainty about whether they did enough.

After the event, support from healthcare professionals, trained responders, family members, or mental health services may be helpful.

References and Further Reading

American Heart Association. 2025 Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care.
https://professional.heart.org/en/science-news/2025-aha-guidelines-for-cpr-and-ecc
American Heart Association. Adult Basic Life Support: 2025 Guidelines.
https://cpr.heart.org/en/resuscitation-science/cpr-and-ecc-guidelines/adult-basic-life-support
American Heart Association. Top Things to Know: 2025 CPR and ECC Guidelines.
https://professional.heart.org/en/science-news/2025-aha-guidelines-for-cpr-and-ecc/top-things-to-know
American Red Cross. How to Perform CPR: Adult CPR Steps.
https://www.redcross.org/take-a-class/cpr/performing-cpr/cpr-steps
American Red Cross. How to Perform Child and Baby CPR.
https://www.redcross.org/take-a-class/cpr/performing-cpr/child-baby-cpr

Medical disclaimer: This article is intended for general education and revision. Resuscitation recommendations may vary with patient age, circumstances, local protocols, and updates to professional guidelines. For an actual emergency, contact local emergency services immediately and follow their instructions. Obtain practical CPR certification from a recognized training provider.