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Cardiopulmonary Resuscitation (CPR) and AED Emergency Protocols

Emergency numbers differ by country. This page uses 911, the number for the United States and Canada. Many other countries use 112, 999, or another number. Find the number for your country.

Cardiopulmonary resuscitation (CPR) is an emergency life-support intervention designed to maintain artificial blood circulation to the brain, myocardium, and vital organs when a person heart ceases mechanical pumping. In out-of-hospital cardiac arrest (OHCA), clinical death begins the instant the heart stops; biological brain death initiates within four to six minutes as oxygen-starved cortical neurons undergo irreversible ischemic necrosis.

High-quality CPR combined with early defibrillation using an Automated External Defibrillator (AED) provides the single greatest determinant of survival for victims of sudden cardiac arrest. Performing continuous chest compressions preserves coronary perfusion pressure, maintains cerebral oxygen delivery, and primes the fibrillating myocardium to accept an electrical shock. Understanding compression mechanics, adhering to standardized depth and rate benchmarks, mastering AED pad application, and adapting techniques for pediatric and drowning victims saves lives.

Immediate Action Priorities: The Adult Cardiac Arrest Chain of Survival

When you witness someone collapse suddenly or encounter an unresponsive individual, execute these sequential life-safety priorities:

Unresponsive Individual Encountered
                │
                ├──> 1. Check Responsiveness & Breathing: Tap shoulders; shout for 10 seconds
                │         └── Agonal gasps are NOT breathing: Treat as cardiac arrest
                │
                ├──> 2. Summon Help: Call 911 / 112 / 999; put phone on speaker
                │
                ├──> 3. Retrieve AED: Direct a specific bystander to fetch defibrillator
                │
                ├──> 4. Hand Placement: Heel of hand on center of chest (lower half of sternum)
                │
                └──> 5. Push Hard & Fast: 100 to 120 bpm; 50 to 60 mm (2.0 to 2.4 in) depth
  1. Assess responsiveness and breathing for 10 seconds:
  2. Kneel beside the person, tap both shoulders firmly, and shout loudly into both ears: "Are you okay? Can you hear me?"
  3. Simultaneously look at the chest and abdomen for normal respiratory movement.
  4. The agonal gasping trap: Do not mistake agonal breathing for normal respiration. Agonal gasps are irregular, heavy, snoring, or snorting reflexive gasps that occur during the first few minutes of cardiac arrest. If the person is unresponsive and not breathing normally, assume cardiac arrest immediately.
  5. Activate emergency medical services (911, 112, 999):
  6. Call your national emergency dispatch number immediately or point directly at a specific bystander and command: "You in the blue shirt, call 911 right now and put it on speaker."
  7. State your exact location and report an adult in sudden cardiac arrest.
  8. Dispatch a bystander for an Automated External Defibrillator (AED):
  9. Point at a second bystander and command: "Go find an AED and bring it back immediately."
  10. Position hands on the sternum:
  11. Ensure the victim is lying flat on their back on a firm, unyielding surface (the floor or pavement; never on a soft mattress).
  12. Place the heel of your primary hand on the center of the bare chest, on the lower half of the breastbone (sternum). Interlock the fingers of your second hand on top.
  13. Deliver high-quality chest compressions:
  14. Push hard and fast at a tempo of 100 to 120 compressions per minute, depressing the chest 50 to 60 millimeters (2.0 to 2.4 inches) with every downward stroke.

The Biomechanics of High-Quality Chest Compressions

Cardiopulmonary resuscitation is mechanical pumping. The goal is building and sustaining Coronary Perfusion Pressure (CPP), the pressure gradient driving blood flow into the coronary arteries during the relaxation phase:

+--------------------------------------------------------------------------+
|                  CORONARY PERFUSION PRESSURE BUILDUP                     |
|                                                                          |
| Blood Pressure                                                           |
|    ▲                                                                     |
| 25 │                     Target CPP Threshold (>15 mmHg)                 |
|    │                 ┌──────────────────────────────────────────────     |
| 15 │             ┌───┘                                                   |
|    │         ┌───┘                                                       |
|  5 │     ┌───┘                                                           |
|  0 └─────┴───────┴───────┴───────┴───────┴───────┴───────┴───────► Time  |
|      Stroke 1    5       10      15      20      25   [ANY PAUSE DROPS   |
|                                                        CPP TO ZERO]      |
|                                                                          |
| MANDATE: Takes 15 to 20 compressions to build pressure; a 3-second      |
| pause causes coronary pressure to crash instantly back to baseline.     |
+--------------------------------------------------------------------------+

The Four Pillars of High-Quality CPR

To achieve maximum hemodynamics and prevent neurological ischemia, every compression must satisfy four clinical metrics established by the American Heart Association and European Resuscitation Council:

Quality Metric Clinical Target Benchmark Physiological Consequence of Failure
Compression Rate 100 to 120 beats per minute Compressing <100 bpm provides inadequate cardiac output; >120 bpm prevents ventricular refilling
Compression Depth 50 to 60 mm (2.0 to 2.4 inches) Depressing <50 mm fails to eject blood from cardiac ventricles; >60 mm causes internal organ trauma
Full Chest Recoil Complete release; zero leaning Leaning on chest between strokes prevents diastolic filling, collapsing coronary perfusion pressure
Minimize Pauses Chest Compression Fraction >80% Pauses >10 seconds cause arterial pressure to drop to zero, requiring 20 fresh compressions to recover

Rescuer Posture and Ergonomics

CPR is physically exhausting. Performing compressions with arm muscles alone leads to rescuer fatigue and shallow, ineffective compressions within 60 seconds:

+--------------------------------------------------------------------------+
|                       RESCUER BIOMECHANICAL ALIGNMENT                    |
|                                                                          |
|                     [Shoulders Directly Over Hands]                      |
|                                   ( o )                                  |
|                                    /|\                                   |
|                      Elbows Locked  |  Arms Completely Straight          |
|                                    / \                                   |
|                                   /   \                                  |
|                                  [HANDS]                                 |
|                        ═════════════════════════                         |
|                         [Patient Sternum (Center)]                       |
|                                                                          |
| MOTION: Pivot entirely from the hips using your upper body weight.       |
| Do not bend your elbows to push; use gravity and core momentum.          |
+--------------------------------------------------------------------------+
  • Lock your elbows: Keep your arms completely straight with elbows locked in extension. Position your shoulders directly over your hands so your upper body weight drives downward vertically.
  • Pivot from the hips: Hinge at your waist, using your core abdominal muscles and gravitational body mass to depress the chest rather than pushing with triceps.
  • Swap compressors every 2 minutes: Even fit individuals experience a significant drop in compression depth after two minutes of continuous CPR without realizing it. If a second rescuer is present, swap positions every two minutes (or every 5 cycles of 30:2, or whenever the AED analyzes). The switch must take less than five seconds.
  • Handling rib fractures: Hearing or feeling a pop or cracking sensation in the chest during compressions is common. This is typically the separation of costal cartilage from the sternum or fractures of brittle ribs, especially in elderly patients. Do not stop CPR. Rib fractures heal; biological brain death from paused compressions is permanent.

Deploying an Automated External Defibrillator (AED)

Most sudden out-of-hospital cardiac arrests are triggered by a lethal cardiac dysrhythmia known as Ventricular Fibrillation (V-Fib) or pulseless Ventricular Tachycardia (V-Tach). In V-Fib, the ventricles quiver chaotically at 300 to 500 beats per minute without pumping blood.

An AED delivers a calibrated biphasic direct-current electrical shock that momentarily depolarizes the entire myocardium, terminating the lethal arrhythmia and allowing the heart natural pacemaker (the sinoatrial node) to resume an organized sinus rhythm:

AED Deployment Sequence
          │
          ├──> 1. Power On: Press button or open lid; machine initiates voice prompts
          │
          ├──> 2. Bare the Chest: Remove shirts, bras; wipe moisture from skin
          │
          ├──> 3. Attach Pads: Apply anterior-lateral pads firmly to bare skin
          │
          ├──> 4. Clear for Analysis: Command "STAND CLEAR"; ensure nobody touches body
          │
          ├──> 5. Deliver Shock: Press flashing button if advised; yell "CLEAR"
          │
          └──> 6. Resume CPR Instantly: Begin chest compressions immediately after shock

Step-by-Step AED Operation

  1. Power on the AED: Open the lid or press the prominent green power button. Modern AEDs provide loud, spoken verbal instructions that guide you through every step.
  2. Expose and prepare the chest:
  3. Strip off all clothing from the torso. Cut clothing with trauma shears found in the AED accessory pouch if necessary.
  4. Wet skin: If the person was pulled from water, or their chest is soaked with perspiration, take five seconds to wipe the chest dry with a towel. Moisture conducts electrical currents across the skin surface, reducing shock delivery to the myocardium and causing skin burns.
  5. Excessive chest hair: If thick chest hair prevents the adhesive pads from making direct contact with skin, press the pads down firmly. If the AED announces "Check pads," rip the pads off forcefully to wax away hair, and apply a fresh set of pads from the kit.
  6. Implanted medical devices: Look for a raised surgical lump or scar beneath the right clavicle indicating a pacemaker or implanted defibrillator. Place the AED pad at least 25 millimeters (1 inch) away from the device; never place the pad directly over an implanted unit.
  7. Transdermal medication patches: If a nitroglycerin, nicotine, or pain patch is on the chest, remove the patch with a gloved hand and wipe the residue away before placing the pad.
  8. Anatomical Pad Placement (Adults and Children over 8 Years / 25 kg / 55 lbs):
  9. Pad 1 (Upper Right): Place on the upper right chest wall, directly beneath the clavicle (collarbone) and to the right of the sternum.
  10. Pad 2 (Lower Left): Place on the lower left lateral chest wall, several centimeters below the left axilla (armpit) along the mid-axillary line.
  11. Heart rhythm analysis: The AED will state: "Analyzing heart rhythm; do not touch the patient." Ensure that chest compressions stop and shout loudly: "Stand clear."
  12. Shock delivery and immediate resumption:
  13. If a shock is advised, the AED charges. Verify nobody is in physical contact with the patient, shout "Everyone clear," and press the flashing shock button (fully automatic AEDs deliver the shock automatically after a countdown).
  14. The critical post-shock rule: The instant the shock is delivered, immediately resume chest compressions. Do not waste time checking for a pulse, breathing, or heart sounds. The heart is stunned following defibrillation and requires mechanical compression to generate cardiac output while recovering normal rhythm.

Hands-Only CPR vs Conventional CPR (With Rescue Breaths)

Understanding when rescue breathing is required versus when Hands-Only CPR is preferred optimizes patient survival:

+--------------------------------------------------------------------------+
|                  HANDS-ONLY CPR VS CONVENTIONAL CPR                      |
|                                                                          |
| CLINICAL SCENARIO               RECOMMENDED TECHNIQUE                    |
| ──────────────────────────────────────────────────────────────────────── |
| Adult Sudden Witnessed Collapse Hands-Only CPR (Continuous compressions) |
| (Out-of-hospital cardiac arrest)| High circulating blood oxygen reserves  |
|                                                                          |
| Pediatric Cardiac Arrest        Conventional CPR (30:2 with breaths)     |
| (Infants and Children)          Primary etiology is respiratory hypoxia  |
|                                                                          |
| Drowning / Submersion Victim    Conventional CPR (5 initial breaths, 30:2)|
|                                 Lungs depleted of oxygen; hypoxic arrest |
|                                                                          |
| Drug Overdose (Opioids)         Conventional CPR (30:2 with breaths)     |
|                                 Respiratory depression precedes arrest   |
+--------------------------------------------------------------------------+

Why Hands-Only CPR Works for Adult Sudden Collapse

When an adult collapses suddenly from primary cardiac arrest, their lungs and arterial blood contain roughly four to six minutes of residual oxygen. The limiting factor in survival is not the lack of oxygen in the blood; it is the lack of circulation to transport that oxygen to the brain:

  • Continuous flow: Hands-Only CPR maintains uninterrupted forward blood flow.
  • Overcoming bystander hesitation: Removing the barrier of mouth-to-mouth rescue breathing dramatically increases the rate of bystander intervention, doubling survival rates.

Conventional 30:2 CPR Execution

For trained providers, or when managing hypoxic arrests:

  1. Deliver 30 high-quality chest compressions.
  2. Open the airway using the head-tilt / chin-lift maneuver: place one hand on the forehead and the fingertips of the other hand beneath the bony chin, tilting the head backward gently.
  3. Pinch the patient soft nostrils closed with your thumb and index finger.
  4. Make a complete, airtight seal with your mouth over the patient mouth.
  5. Blow steadily for 1.0 second, watching for visible chest rise.
  6. Deliver a second breath (total pause for both breaths must not exceed 5 seconds).
  7. Immediately resume chest compressions. If the chest does not rise, re-tilt the head and attempt one more breath; never attempt more than two breaths per cycle before returning to compressions.

Pediatric and Infant CPR Modifications

Cardiac arrest in infants and young children is rarely caused by primary cardiac arrhythmias. It is almost always secondary to progressive respiratory failure, airway obstruction, severe asthma, or drowning:

+--------------------------------------------------------------------------+
|                     PEDIATRIC CPR SPECIFICATION MATRIX                   |
|                                                                          |
| PARAMETER           INFANTS (<1 YEAR)            CHILDREN (1 TO PUBERTY) |
| ──────────────────────────────────────────────────────────────────────── |
| Hand Placement      2 fingers on sternum or      1 or 2 hands on lower   |
|                     2-thumb encircling technique half of breastbone      |
| Compression Depth   40 mm (1.5 inches)           50 mm (2.0 inches)      |
|                     (1/3 of chest depth)         (1/3 of chest depth)    |
| Compression Rate    100 to 120 bpm               100 to 120 bpm          |
| Compression Ratio   30:2 (Single rescuer)        30:2 (Single rescuer)   |
|                     15:2 (Two rescuers)          15:2 (Two rescuers)     |
| AED Pad Placement   Anterior-Posterior           Anterior-Lateral or     |
|                     (Chest and Back)             Anterior-Posterior      |
| Phone / Call Order  Perform 2 minutes CPR FIRST  Perform 2 minutes CPR   |
| (If alone, no phone)| before leaving to call      FIRST if alone          |
+--------------------------------------------------------------------------+

Infant CPR Technique (Under 1 Year Old)

  1. Check responsiveness: Tap the soles of the infant feet firmly and call their name. Never shake an infant. Check breathing for 10 seconds.
  2. Compression mechanics:
  3. Place the infant on a firm, elevated surface or hard floor.
  4. Single rescuer: Place two fingers in the center of the chest, just below the inter-mammary line (nipple line). Depress the chest 40 millimeters (1.5 inches) at 100 to 120 bpm.
  5. Two rescuers: Use the two-thumb encircling-hands technique. Wrap your hands around the infant rib cage and place both thumbs side-by-side on the lower half of the sternum. Squeeze the rib cage while depressing the thumbs downward.
  6. Rescue breaths: Deliver small, gentle puffs of air from your cheeks (not a full lung exhalation) covering both the infant nose and mouth simultaneously with your mouth.
  7. Infant AED pad placement: Use pediatric attenuator pads if available. Apply one pad to the center of the chest and the second pad to the center of the upper back between the shoulder blades (anterior-posterior orientation) to prevent pads from touching.

Resuscitation for Drowning and Cold Water Immersion

Drowning represents a severe, asphyxial cardiac arrest that requires modifying the standard sequence:

Drowning Resuscitation Protocol
              │
              ├──> 1. Water Extraction: Remove victim to solid ground immediately
              │
              ├──> 2. Five Initial Breaths: Deliver 5 rescue breaths before compressions
              │
              ├──> 3. Standard 30:2 Cycles: Continue compressions and ventilations
              │
              ├──> 4. Dry Chest for AED: Towel-dry skin prior to attaching pads
              │
              └──> 5. Rewarming Persistence: Continue CPR in hypothermic victims
  • Five initial rescue breaths: Because the heart stopped due to profound oxygen depletion, begin resuscitation by delivering 5 rescue breaths immediately. Follow with standard 30 compressions to 2 breaths.
  • Foam in the airway: Drowning victims frequently produce thick, white or pink pulmonary edema foam in their mouth. Do not waste time trying to suction or wipe all foam away; deliver ventilations directly through the foam.
  • The hypothermia doctrine: If a person was submerged in icy water, severe hypothermia slows cerebral metabolic demand, protecting brain tissue from hypoxia. Do not terminate resuscitation efforts in hypothermic individuals. Maintain continuous CPR until the patient core temperature is restored in an emergency department.

Post-Resuscitation Care and Rescuer Debriefing

  1. Return of Spontaneous Circulation (ROSC): If the patient begins moving, coughing, groaning, or breathing normally, stop chest compressions. Place them on their side in the lateral recovery position to protect their airway against vomiting. Leave the AED pads attached; cardiac arrest recurs in up to 40 percent of successfully resuscitated patients before paramedics arrive.
  2. Emotional impact on the rescuer: Performing CPR is traumatic. Rescuers frequently experience intrusive thoughts, sleep disruption, and anxiety. Talk to mental health professionals or trusted peers. Understand that sudden cardiac arrest carries an out-of-hospital mortality rate exceeding 85 to 90 percent; stepping forward to perform CPR gave that individual their only chance of survival.
  3. Course recommendation: CPR cannot be mastered solely by reading a guide. Practicing hands-on psychomotor compressions on certified feedback manikins is essential. Enroll in a certified cardiopulmonary resuscitation and automated external defibrillator certification course through the American Heart Association, Red Cross, St John Ambulance, or national resuscitation councils.

Frequently asked questions

The official compression rate for adult CPR is 100 to 120 compressions per minute, to a depth of at least 50 mm (2 inches) but no greater than 60 mm (2.4 inches). Allow the chest to recoil completely between each compression to permit full cardiac refill.

Can you perform CPR if you are not trained in rescue breaths?

Yes. If you are untrained or uncomfortable delivering mouth-to-mouth breaths, perform Hands-Only CPR by delivering uninterrupted chest compressions at 100 to 120 beats per minute. Hands-Only CPR is as effective as conventional CPR for adult sudden cardiac arrest during the first several minutes.

What should you do if you hear or feel ribs cracking during CPR?

Continue chest compressions without stopping. Sensation or sound of cracking ribs or cartilage separation frequently occurs during effective CPR due to the downward force required to compress the heart between the sternum and spine. Pausing compressions because of broken ribs is fatal.

Can an automated external defibrillator (AED) shock someone accidentally if they do not need it?

No. An automated external defibrillator uses advanced internal rhythm analysis software that will only permit a shock to be delivered if it detects ventricular fibrillation or pulseless ventricular tachycardia. It is impossible to shock someone whose heart is beating normally.