4 Cardiac Arrest and Resuscitation

A practical guide to recognizing adult cardiac arrest, delivering CPR and rhythm-based resuscitation, addressing reversible causes, and responding when circulation returns.

Recognize arrest and activate help

In an adult who is unresponsive and not breathing normally—including one who is gasping—activate the emergency response system and obtain an AED or monitor-defibrillator. A healthcare professional should check for a pulse for no more than $10$ seconds. If no definite pulse is felt, start CPR; if unsure whether a pulse is present, begin compressions.

A lone rescuer without a phone should leave briefly to activate emergency response and retrieve an AED, then return and begin CPR. Follow local protocols and dispatcher instructions. Start CPR while help and the defibrillator are being prepared.

Deliver

Place the heel of one hand in the center of the chest, on the lower half of the breastbone, and place the other hand on top. Compress at $100$ – $120$ per minute, to a depth of at least $2$ inches ( $5$ cm), while avoiding depths greater than $2.4$ inches ( $6$ cm). Allow full chest recoil and do not lean on the chest between compressions.

Keep interruptions as short and infrequent as possible. Change compressors about every $2$ minutes, or sooner if fatigued.

Without an advanced airway, use $30$ compressions to $2$ breaths. Give each breath over about $1$ second—just enough to make the chest rise—and avoid excessive ventilation. With an advanced airway, continue compressions without pauses and give $1$ breath every $6$ seconds ( $10$ per minute).

If available, waveform capnography helps confirm and monitor an endotracheal tube and assess CPR quality. A low or falling end-tidal CO₂ should prompt reassessment of compressions and ventilation; a sudden increase may signal ROSC.

Assess the rhythm and defibrillate safely

Attach the monitor-defibrillator as soon as possible and classify the rhythm as shockable or nonshockable. Check the rhythm about every $2$ minutes, minimizing the pause. Resume CPR immediately after each shock; do not pause for a routine pulse check unless an organized rhythm or other signs suggest ROSC.

Use the defibrillator manufacturer’s recommended biphasic energy, often an initial $120$ – $200$ J. If the recommended energy is unknown, use the maximum available. Subsequent doses should be equivalent, and higher doses may be considered. For a monophasic defibrillator, use $360$ J. Follow the device and local protocol, and ensure rescuers are clear before delivering a shock.

Follow the rhythm-specific pathways

Ventricular fibrillation or pulseless ventricular tachycardia

For shockable rhythms, deliver a shock, then immediately resume CPR for $2$ minutes and establish IV or IO access. Reassess the rhythm. If it remains VF or pulseless VT, shock again and immediately resume CPR. Give epinephrine $1$ mg IV/IO every $3$ – $5$ minutes; consider an advanced airway and waveform capnography.

If the rhythm remains shockable after another cycle, shock again and resume CPR. For refractory VF or pulseless VT, give amiodarone $300$ mg IV/IO, then $150$ mg if needed, or lidocaine $1$ – $1.5$ mg/kg, then $0.5$ – $0.75$ mg/kg if needed. Continue treating reversible causes.

Asystole or pulseless electrical activity

Do not defibrillate asystole or PEA. Resume CPR immediately, establish IV/IO access, and give epinephrine $1$ mg IV/IO as soon as possible, then every $3$ – $5$ minutes. Recheck the rhythm about every $2$ minutes, continue CPR, and actively search for and treat reversible causes. If the rhythm becomes VF or pulseless VT, switch to the shockable pathway.

Search for reversible causes

Look for causes that can be corrected during resuscitation:

Hs: hypovolemia; hypoxia; hydrogen ion (acidosis); hypo- or hyperkalemia; hypothermia.
Ts: tension pneumothorax; cardiac tamponade; toxins; pulmonary thrombosis (for example, pulmonary embolism); coronary thrombosis.

Use the history, examination, rhythm, and available tests to guide treatment. Examples include addressing severe blood loss, improving oxygenation, or treating suspected tension pneumothorax. Do not let investigations or procedures unnecessarily interrupt compressions or delay defibrillation.

Respond when circulation returns

Signs of ROSC include a palpable pulse, purposeful movement, a measurable blood pressure, or a sudden sustained rise in end-tidal CO₂. Confirm circulation and transition promptly to post-arrest care.

Support the airway, oxygenation, ventilation, and blood pressure; obtain a $12$ -lead ECG; and evaluate and treat the cause of the arrest.