Cardiopulmonary resuscitation (CPR) combined with automated external defibrillation (AED) is the foundational emergency intervention for cardiac arrest — the sudden cessation of effective cardiac output leading to global ischaemia. Cardiac arrest claims approximately 300,000 lives annually in the United States and 420,000 in Europe, with survival rates that remain below 10% for out-of-hospital cardiac arrest (OHCA) despite decades of research. Outcomes are directly tied to the speed and quality of CPR initiation, defibrillation delivery, and return of spontaneous circulation (ROSC). Advanced life support (ALS) protocols — standardised by the International Liaison Committee on Resuscitation (ILCOR) and implemented through national guidelines (Resuscitation Council UK, AHA, ERC) — structure resuscitation into a systematic 2-minute cycle of CPR (compressions:ventilations 30:2) interrupted only for rhythm check and defibrillation attempts. Shockable rhythms (ventricular fibrillation [VF] and pulseless ventricular tachycardia [pVT]) are treated with immediate defibrillation: biphasic defibrillators at 120–200 J (first shock) and 150–360 J (subsequent shocks); monophasic defibrillators at 360 J for all shocks. Non-shockable rhythms (pulseless electrical activity [PEA] and asystole) require continuous CPR with treatment of reversible causes (the '4Hs and 4Ts'). Adrenaline (epinephrine) 1 mg IV is administered every 3–5 minutes in all cardiac arrest rhythms; amiodarone 300 mg IV is given after the third shock in VF/pVT. Post-ROSC care targets: SBP >100 mmHg, SpO₂ 94–98%, PaCO₂ 35–45 mmHg, and targeted temperature management to prevent secondary neurological injury.
CPR cycle: 30 chest compressions : 2 rescue breaths (30:2) for adults; rate 100–120/min; depth 5–6 cm; full chest recoil; defibrillation: biphasic 120–200 J (first shock), 150–360 J (subsequent); monophasic 360 J; adrenaline 1 mg IV q3–5min; amiodarone 300 mg IV after 3rd shock, then 150 mg after 5th; reversible causes: 4Hs (Hypoxia, Hypovolaemia, Hyper/Hypokalaemia, Hypothermia) + 4Ts (Tension pneumothorax, Tamponade, Thrombosis PE/coronary, Toxins)
- 1Confirm cardiac arrest: unresponsive, not breathing normally (absent or gasping breaths), no pulse palpable within 10 seconds — call for help, call 999/911, and start CPR immediately; do not delay compressions to look for a pulse for more than 10 seconds.
- 2Deliver high-quality CPR: position hands on the lower half of the sternum; compress at rate 100–120/min; depth 5–6 cm (2–2.4 inches); allow full chest recoil after each compression; minimise interruptions to compressions (pause <10 seconds for rhythm check only); maintain 30:2 ratio until advanced airway is placed, then continuous compressions at 100–120/min with ventilation every 6 seconds.
- 3Attach AED/defibrillator as soon as available: analyse rhythm; if VF or pVT is identified, deliver shock immediately (biphasic 120–200 J for first shock); immediately resume CPR after shock without checking pulse; continue 2-minute CPR cycles.
- 4Secure IV or IO access during CPR; administer adrenaline (epinephrine) 1 mg IV as soon as access is established for non-shockable rhythms (PEA/asystole), or after the 3rd shock in VF/pVT; repeat every 3–5 minutes.
- 5Administer amiodarone 300 mg IV after the third shock in refractory VF/pVT; a second dose of 150 mg IV may be given after the fifth shock if VF/pVT persists.
- 6Systematically identify and treat reversible causes during every CPR cycle using the 4Hs and 4Ts mnemonic: Hypoxia — optimise oxygenation; Hypovolaemia — IV fluid bolus; Hyper/Hypokalaemia/metabolic — treat with ECG guidance; Hypothermia — active rewarming; Tension pneumothorax — needle decompression; Tamponade — pericardiocentesis or surgical drainage; Thrombosis (PE or coronary) — thrombolysis or primary PCI/surgical embolectomy; Toxins — specific antidotes.
- 7After ROSC, initiate post-cardiac arrest care: maintain airway with endotracheal intubation if not already placed; target SpO₂ 94–98% (avoid hyperoxia); maintain SBP >100 mmHg with fluids/vasopressors; target PaCO₂ 35–45 mmHg (avoid hypo- and hypercapnia); 12-lead ECG for STEMI identification and emergency coronary angiography; initiate targeted temperature management (TTM) at 32–36°C if comatose.
Every minute without defibrillation in VF reduces survival by 7–10%; bystander CPR doubles or triples survival rates.
VF is the most shockable and potentially reversible cardiac arrest rhythm; witnessed VF with early defibrillation has the best survival outcomes — some series report >50% survival when AED is applied within 3 minutes.
Tension pneumothorax is a reversible cause (4T) of PEA; needle decompression may restore circulation.
In PEA and asystole, CPR without treatment of the underlying cause is futile; systematic 4H/4T assessment during every 2-minute CPR cycle is the key to ROSC in non-shockable rhythms.
Amiodarone reduces the recurrence of VF and pVT after defibrillation and is the only antiarrhythmic with Class I evidence in cardiac arrest.
Refractory VF (persisting after ≥3 shocks) has a poor prognosis without additional pharmacotherapy; amiodarone improves short-term survival to hospital admission, though its effect on discharge survival is less clear.
Hyperoxia (SpO₂ >98%) and hypocapnia post-ROSC independently worsen neurological outcomes — avoid aggressive over-ventilation.
Post-cardiac arrest syndrome involves whole-body ischaemia-reperfusion injury; precise physiological targets in the first 24–72 hours are as important as achieving ROSC itself.
Emergency service dispatchers use telephone CPR protocols to guide bystanders through hands-only CPR while ambulance services respond, improving outcomes in out-of-hospital cardiac arrest, enabling practitioners to make well-informed quantitative decisions based on validated computational methods and industry-standard approaches
AEDs deployed in airports, shopping centres, sports venues, and schools enable lay responders to defibrillate VF within minutes of collapse — dramatically improving community cardiac arrest survival, helping analysts produce accurate results that support strategic planning, resource allocation, and performance benchmarking across organizations
Hospital crash teams use ALS algorithms on resuscitation trolleys and simulation training to ensure systematic, high-quality CPR delivery during in-hospital cardiac arrests, allowing professionals to quantify outcomes systematically and compare scenarios using reliable mathematical frameworks and established formulas
Cardiac intensive care units use post-ROSC care bundles to implement TTM, coronary angiography pathways, and neuroprognostication protocols for comatose cardiac arrest survivors, supporting data-driven evaluation processes where numerical precision is essential for compliance, reporting, and optimization objectives
Sports medicine teams at professional sporting events carry AEDs and train coaching staff in CPR to manage commotio cordis and sudden cardiac arrest in young athletes, which requires precise quantitative analysis to support evidence-based decisions, strategic resource allocation, and performance optimization across diverse organizational contexts and professional disciplines
Drowning cardiac arrest
Drowning cardiac arrest is typically hypoxic in origin (not primary cardiac); rescue breathing is therefore more important than in adult cardiac arrest — a 5 initial rescue breath approach is used (as in paediatric ALS). Hypothermia is common in cold-water drowning and actually provides some neuroprotection — prolonged resuscitation (>60 minutes) is warranted; no patient is dead until warm and dead.
AED use in children
AEDs can safely be used in children over 1 year. Paediatric pads/attenuators should be used for children <8 years or <25 kg where available — they reduce energy delivery to 50–75 J. If only adult pads are available, they should still be used in a child rather than withholding defibrillation. Place one pad anterior (sternum) and one posterior (back) in small children to avoid pad overlap.
Pregnancy and cardiac arrest
Standard CPR algorithm applies in pregnancy, with left lateral uterine displacement (manual) to relieve aortocaval compression during compressions. Defibrillation is safe and should not be delayed. If ROSC is not achieved by 4 minutes of cardiac arrest in a gestation ≥20 weeks, perimortem caesarean section should be performed immediately — it removes the IVC compression, restoring CPR effectiveness, and may save the fetus.
Traumatic cardiac arrest
Traumatic cardiac arrest (TCA) follows a different protocol: airway management and haemorrhage control take priority over CPR; bilateral thoracostomies are performed immediately to relieve tension pneumothorax; resuscitative thoracotomy is indicated for penetrating trauma with loss of signs of life within 10 minutes; adrenaline is not routinely given in TCA.
| Rhythm | Shockable? | First Drug | Energy (Biphasic) |
|---|---|---|---|
| VF (ventricular fibrillation) | Yes | Adrenaline after 3rd shock; amiodarone 300 mg after 3rd shock | 120–200 J first; escalate for subsequent |
| pVT (pulseless VT) | Yes | Adrenaline after 3rd shock; amiodarone 300 mg after 3rd shock | 120–200 J first; escalate for subsequent |
| PEA (pulseless electrical activity) | No | Adrenaline 1 mg IV immediately; treat 4Hs/4Ts | No defibrillation — compressions only |
| Asystole | No | Adrenaline 1 mg IV immediately; atropine not recommended (2010+) | No defibrillation — compressions only |
What is the 30:2 compression-to-ventilation ratio based on?
The 30:2 ratio was adopted by ILCOR in 2005 based on evidence that excessive ventilation during CPR raises intrathoracic pressure, reduces venous return, and impairs coronary perfusion pressure. 30 compressions:2 breaths optimises the compression fraction and allows adequate CO₂ clearance without haemodynamic compromise. In children, a 15:2 ratio (two rescuers) is recommended because paediatric arrest is more often respiratory in origin.
What energy levels should be used for defibrillation?
Biphasic defibrillators: 120–200 J for the first shock; use the same or higher energy for subsequent shocks (up to the device maximum). If the effective energy is unknown, use 200 J as default. Monophasic defibrillators (becoming rare): 360 J for all shocks. Biphasic waveforms are more effective with lower energy and cause less myocardial damage than monophasic waveforms.
When should adrenaline be given in cardiac arrest?
In non-shockable rhythms (PEA/asystole): adrenaline 1 mg IV as soon as vascular access is established, then every 3–5 minutes. In shockable rhythms (VF/pVT): after the third shock, then every 3–5 minutes during alternating 2-minute CPR cycles. Early adrenaline in non-shockable rhythms improves ROSC rates; its role in shockable rhythms is more complex and timing matters.
What are the 4Hs and 4Ts?
The 4Hs and 4Ts are the reversible causes of cardiac arrest that should be systematically assessed during CPR: 4Hs = Hypoxia, Hypovolaemia, Hyper/Hypokalaemia/metabolic, Hypothermia; 4Ts = Tension pneumothorax, cardiac Tamponade, Thrombosis (pulmonary embolism or acute coronary syndrome), Toxins. Identifying and treating a reversible cause is the most important determinant of survival in PEA and asystole.
What is targeted temperature management (TTM) and who should receive it?
TTM involves cooling the patient to 32–36°C for 24 hours after ROSC in comatose cardiac arrest survivors. It reduces cerebral metabolic demand during the vulnerable post-arrest reperfusion period. The TTM2 trial (2021) showed no difference between 33°C and 37.5°C targets, but all centres maintained strict fever prevention (<37.7°C). TTM is recommended for all comatose (GCS ≤8) adult survivors of out-of-hospital cardiac arrest with any initial rhythm, and for in-hospital cardiac arrest in selected centres.
When should CPR be stopped?
CPR should be continued as long as there is a realistic chance of achieving ROSC. Resuscitation may be terminated after: ≥20–30 minutes of CPR without ROSC in a non-hypothermic patient with no reversible cause identified; clinical evidence of irreversibility (rigor mortis, decapitation, decomposition); confirmed DNAR order; or physician/team decision based on clinical context. Prolonged CPR >60 minutes can achieve ROSC in selected cases (hypothermia, drug overdose, ECMO-CPR).
Is hands-only CPR effective?
Yes. Continuous chest compressions without ventilation (hands-only/compression-only CPR) is as effective as 30:2 CPR for the first 4–6 minutes of witnessed cardiac arrest in adults, because residual oxygen in the lungs and circulation is sufficient initially. Hands-only CPR is strongly recommended for bystanders without formal training or those unwilling to perform mouth-to-mouth ventilation — removing the ventilation barrier significantly increases bystander CPR rates.
What is ECMO-CPR (ECPR)?
Extracorporeal CPR (ECPR) involves establishing veno-arterial ECMO (extracorporeal membrane oxygenation) during ongoing cardiac arrest, bypassing the heart and lungs to provide systemic circulation and oxygenation. ECPR can support perfusion indefinitely, allowing time for coronary angiography, thrombolysis, or treatment of reversible causes. It is used in selected refractory cardiac arrest patients (<75 years, witnessed arrest, within 60 minutes of collapse) at specialised ECMO-capable centres.
Pro Tip
High-quality chest compressions are the single most important intervention in cardiac arrest. Before any other consideration, ensure compressions are at 100–120/min, to a depth of 5–6 cm, with full recoil, and minimal interruptions. A 10% improvement in CPR quality translates to a measurable improvement in survival — more than any pharmacological intervention.
Did you know?
The first successful defibrillation of a human heart was performed by Claude Beck in 1947 at the Cleveland City Hospital on a 14-year-old boy whose heart had fibrillated during surgery. Beck used an open-chest technique with paddles applied directly to the heart — external defibrillation did not come until 1956, when Paul Zoll shocked a patient's heart through the intact chest wall for the first time.
References
- ›Resuscitation Council UK — Advanced Life Support, 8th Edition (2021)
- ›AHA — CPR and ECC Guidelines (2020)
- ›ERC Guidelines 2021 — Adult Advanced Life Support (Soar J et al.)
- ›Nielsen N et al. — TTM Trial — Targeted Temperature Management (NEJM 2013)
- ›Dankiewicz J et al. — TTM2 Trial — Hypothermia vs Normothermia (NEJM 2021)