Cardiopulmonary resuscitation, or CPR, is an emergency technique that manually pumps blood through the body when someone’s heart has stopped beating. It combines chest compressions and, in some cases, rescue breaths to keep oxygen flowing to the brain and vital organs until advanced medical help arrives. When performed correctly, CPR can deliver up to 33% of the heart’s normal output, which is often enough to keep a person alive during those critical minutes.
Why CPR Matters: The Clock Starts Immediately
When the heart stops, the brain loses consciousness within 4 to 10 seconds. Electrical activity in the brain flatlines within 10 to 30 seconds. Because brain cells have almost no energy reserves of their own, cellular damage begins the moment blood flow stops. Even CPR, which restores roughly 25% of normal blood flow to the brain, falls below the 40 to 50% threshold needed to fully protect neurons from injury. But that partial flow buys time, and time is the difference between life and death.
Without any intervention, permanent brain damage and death follow within minutes. With bystander CPR, the survival rate to hospital discharge is approximately 34%. When a bystander also uses an automated external defibrillator (AED), survival jumps to 38%, compared to just 9% with no intervention at all. Every minute without CPR reduces the chance of survival, which is why starting immediately matters more than performing it perfectly.
How Chest Compressions Work
Chest compressions are the core of CPR. When you push hard and fast on the center of someone’s chest, you increase the pressure inside the chest cavity. This squeezes the heart between the breastbone and spine, forcing blood out into the arteries. When you release, the chest recoils and the heart refills with blood. This cycle mimics the heart’s natural pumping action, though at a fraction of its normal efficiency.
The key measurement during compressions is something called coronary perfusion pressure, the pressure difference that keeps blood flowing through the heart muscle itself. Every time compressions are interrupted, even for a few seconds, that pressure drops and takes multiple compressions to rebuild. This is why minimizing pauses is one of the most important things a rescuer can do.
Adult CPR Technique
Current American Heart Association guidelines recommend compressing the chest at least 5 centimeters (about 2 inches) deep but no more than 6 centimeters. Research involving over 10,700 patients found improved survival when compression depth reached at least 5 cm, while going beyond 6 cm was associated with reduced survival. The target rate is 100 to 120 compressions per minute. Studies of more than 13,700 patients showed the best outcomes in the 100 to 119 range.
If you’re trained in full CPR, you alternate 30 compressions with 2 rescue breaths. Each breath should last about 1 second, using a normal breath (not a deep one), and you’re looking for the chest to visibly rise. The breaths deliver oxygen to the lungs, but they also come with a tradeoff: positive-pressure ventilation increases chest pressure and can temporarily reduce blood flow back to the heart. That’s why the ratio favors compressions so heavily.
Hands-Only CPR for Untrained Bystanders
If you haven’t been trained in CPR or aren’t comfortable giving rescue breaths, hands-only CPR (continuous chest compressions without breaths) is not just acceptable, it’s actually more effective when performed by bystanders. A meta-analysis pooling multiple studies found that 11.5% of patients receiving compression-only CPR survived to hospital discharge, compared to 9.4% of those receiving standard CPR with breaths from bystanders. That translates to a 24% greater likelihood of survival with the simpler technique.
The likely explanation is straightforward: untrained rescuers who attempt rescue breaths tend to pause compressions for too long, and those pauses let coronary perfusion pressure collapse. Continuous compressions maintain steadier blood flow. For bystanders witnessing an adult collapse, the recommendation is simple: call emergency services, then push hard and fast on the center of the chest without stopping.
CPR for Infants and Children
Children and infants need a modified approach because their bodies are smaller and the causes of cardiac arrest differ. In adults, the heart itself usually fails first. In children, cardiac arrest more often results from breathing problems, which means rescue breaths play a more important role.
For newborns, the compression-to-breath ratio drops to 3:1, targeting 90 compressions and 30 breaths per minute. Instead of using the heel of the hand, rescuers use two fingers or two thumbs placed on the breastbone. Compression depth for newborns is shallower, around 3 to 4 centimeters. For older children, the technique scales up toward the adult method depending on the child’s size, but rescue breaths remain a standard part of the protocol rather than optional.
The Role of Defibrillators
CPR keeps blood moving, but it rarely restarts the heart on its own. Most sudden cardiac arrests in adults are caused by an electrical malfunction where the heart quivers chaotically instead of pumping. The fix for that is an electrical shock from a defibrillator, which resets the heart’s rhythm so it can beat normally again.
Automated external defibrillators (AEDs) are designed for anyone to use. They provide voice prompts, analyze the heart’s rhythm automatically, and only deliver a shock if one is needed. The survival impact is dramatic: one study found that applying an AED nearly tripled the odds of survival compared to CPR alone (24% vs. 9%), and when the AED actually delivered a shock, survival reached 38%. AEDs with a 1.75-fold greater likelihood of survival after adjusting for other factors. You’ll find them in airports, gyms, schools, and many public buildings, usually in wall-mounted cases marked with a heart symbol.
The Chain of Survival
CPR is one link in a six-step chain that gives cardiac arrest victims the best chance. The American Heart Association defines these links as:
- Recognition and activation: Identifying that someone is in cardiac arrest and calling emergency services
- Early CPR: Starting chest compressions immediately
- Rapid defibrillation: Using an AED as soon as one is available
- Advanced resuscitation: Treatment by paramedics and emergency medical teams
- Post-cardiac arrest care: Hospital-based stabilization and treatment
- Recovery: Rehabilitation, follow-up care, and psychological support
Each link depends on the one before it. The most advanced hospital care can’t undo the damage from several minutes without blood flow. Bystanders control the first three links, which is why public CPR training has such an outsized impact on survival rates.
Physical Injuries From CPR
Effective CPR requires significant force, and injuries to the person receiving it are common. A systematic review found that about 60% of CPR recipients sustain some form of injury. Rib fractures are the most frequent, occurring in roughly 55% of cases. Breastbone fractures happen in about 24%. Lung bruising occurs in around 20% of cases, and bleeding behind the breastbone in about 12%. Liver injuries are less common, at approximately 3%.
These numbers can sound alarming, but context matters. CPR is performed on people who are clinically dead. Broken ribs heal. Without CPR, the alternative is not a better outcome; it’s death. If you feel a crack or pop while performing compressions, keep going. You’re doing it right.
Legal Protections for Bystanders
Every U.S. state has some version of Good Samaritan laws that protect people who voluntarily provide emergency care. These laws shield bystanders from negligence claims as long as they act in good faith, don’t expect payment, and don’t engage in reckless or willful misconduct. The principle is simple: public policy benefits when people help each other in emergencies, and the legal system shouldn’t punish someone for trying to save a life. The protection covers ordinary mistakes, meaning you won’t face liability for imperfect technique. It does not cover grossly negligent or intentionally harmful actions, but performing CPR on someone in cardiac arrest falls squarely within the protected category.