Cardiopulmonary Resuscitation (CPR) is an emergency medical procedure used to preserve brain and organ viability in a person experiencing cardiac arrest, defined as the abrupt cessation of effective cardiac mechanical activity resulting in loss of systemic circulation.

When the heart stops pumping, cerebral perfusion drops to zero, and irreversible neuronal injury begins within 3 to 5 minutes. CPR artificially replaces the mechanical function of the heart and partially substitutes for pulmonary ventilation, allowing limited but critical oxygen delivery to the brain, myocardium, and vital organs until defibrillation or advanced life support can restore spontaneous circulation.

Pathophysiology of Cardiac Arrest

During cardiac arrest:

• Coronary perfusion pressure collapses
• Cerebral blood flow ceases
• Myocardial oxygen delivery stops
• Electrical instability rapidly worsens

Without intervention, ventricular fibrillation or pulseless ventricular tachycardia degrades into asystole, which is far more difficult to reverse.

CPR counteracts this by generating forward blood flow through:

• Compression of the ventricles between the sternum and spine
• Increased intrathoracic pressure
• Passive ventilation via chest recoil

These mechanisms produce approximately 20 to 30 percent of normal cardiac output, which is often enough to prevent hypoxic brain injury and maintain myocardial viability until defibrillation can occur.

How Chest Compressions Work

High-quality chest compressions:

• Are performed at 100 to 120 per minute
• At a depth of 2 to 2.4 inches (5 to 6 cm) in adults
• With full chest recoil
• With minimal interruptions

Each compression generates a small stroke volume, creating perfusion to the coronary and cerebral circulation. Full recoil allows venous return to refill the heart, maintaining preload for the next compression.

Interruptions longer than 10 seconds cause coronary perfusion pressure to drop dramatically and require many compressions to rebuild.

Role of Defibrillation

CPR alone rarely restarts the heart.

Most adult cardiac arrests are caused by ventricular fibrillation (VF) or pulseless ventricular tachycardia (VT). These rhythms require defibrillation, which depolarizes the myocardium simultaneously and allows the sinoatrial node to regain control.

CPR preserves myocardial oxygenation and ATP levels, which makes defibrillation more likely to succeed.

Without CPR, defibrillation is often ineffective because the myocardium becomes too ischemic to respond.

Oxygenation and Ventilation

In the first several minutes of adult sudden cardiac arrest, the blood still contains significant oxygen. That is why Hands-Only CPR is effective for adult collapse.

Chest compressions circulate that existing oxygen.

For pediatric, drowning, opioid, and respiratory-origin arrests, ventilation becomes more critical because hypoxia is the primary cause of collapse.

This is why professional CPR training includes compression-to-ventilation ratios and airway management.

Cerebral Protection

The brain is the most time-sensitive organ in cardiac arrest.

Without CPR:

• Neuronal injury begins at ~3 minutes
• Severe injury occurs by 5 minutes
• Brain death becomes likely after 8–10 minutes

With CPR, cerebral blood flow is maintained at approximately 30 percent of normal, which dramatically increases the likelihood of neurologically intact survival after resuscitation.

Why CPR Must Start Immediately

Every minute without CPR:

• Survival drops by 7 to 10 percent
• The myocardium becomes less responsive to defibrillation
• The probability of ROSC (return of spontaneous circulation) decreases

Early CPR preserves both electrical and mechanical viability of the heart.

Why CPR Training Matters

CPR effectiveness depends on:

• Compression depth
• Rate
• Recoil
• Hand placement
• Minimal pauses
• Proper AED timing

Poor-quality CPR is almost as dangerous as no CPR at all.

Training creates neuromuscular memory, enabling people to perform high-quality compressions under stress when fine motor skills and cognition degrade.

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In Summary

CPR is not symbolic.

It is mechanical life support.

It maintains cerebral and coronary perfusion, preserves myocardial viability, and enables successful defibrillation and advanced resuscitation.

In cardiac arrest, CPR does not save lives by itself.
It makes survival possible.

And it starts with trained hands.