Cardiac arrest - out of hospital care
Exam Tips
- In OSCEs, agonal gasps in an unresponsive adult should be treated as cardiac arrest; do not delay CPR for prolonged reassessment.
- State the adult CPR metrics clearly: compressions at 100-120/min, depth 5-6 cm, ratio 30:2, and minimal interruptions.
- Prioritise chain of survival language: early recognition, call 999, early CPR, early defibrillation, and advanced care.
- For ALS viva questions, remember key arrest drugs and doses: adrenaline 1 mg IV/IO every 3-5 minutes; amiodarone 300 mg after 3rd shock (then 150 mg after 5th if needed).
- If asked about poor-outcome rhythms, emphasise that asystole/PEA survival is low unless a reversible cause is rapidly identified and treated.
- See Figure: Resuscitation Council UK adult basic life support algorithm (use this as your mental sequence in exams).
Definition
Out-of-hospital cardiac arrest is the abrupt cessation of effective cardiac mechanical activity in the community setting, causing immediate circulatory collapse and loss of consciousness. Clinically it is identified by unresponsiveness with absent or abnormal breathing (including agonal gasps), and it requires immediate emergency activation, high-quality CPR, and early defibrillation where indicated.
Pathophysiology
Most adult out-of-hospital cardiac arrests are triggered by acute coronary ischaemia or structural/electrical heart disease, leading to malignant rhythms (especially ventricular fibrillation or pulseless ventricular tachycardia) or non-shockable rhythms (pulseless electrical activity/asystole). Global cessation of perfusion rapidly causes cerebral and myocardial hypoxia, worsening acidosis and cellular failure; this creates a self-perpetuating cycle unless the chain of survival is restored. Reversible precipitants are classically approached as the 4 Hs and 4 Ts: hypoxia, hypovolaemia, hypo-/hyperkalaemia and other metabolic derangement, hypothermia; tension pneumothorax, cardiac tamponade, toxins, and thromboembolism (coronary or pulmonary).
Risk Factors
- Coronary artery disease and previous myocardial infarction
- Left ventricular systolic dysfunction/heart failure
- Cardiomyopathies (including hypertrophic cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy)
- Inherited arrhythmia syndromes (for example long QT syndrome, Brugada syndrome)
- Valvular heart disease
- Medical/surgical emergencies such as pulmonary embolism or tension pneumothorax
- Drug toxicity and illicit drug use (opioids causing hypoxic arrest; stimulants such as cocaine/amphetamines causing ischaemia/arrhythmia)
- Smoking, malnutrition/eating disorders, and chronic comorbidity burden
Clinical Features
Symptoms
- Usually none reported at the point of arrest because the patient is unconscious
- Possible preceding chest pain, palpitations, dyspnoea, or syncope
- Possible prodromal collapse after exertion or acute emotional stress
Signs
- Unresponsive and not breathing normally
- Agonal breathing/gasping (treat as cardiac arrest, not normal respiration)
- No signs of life, with pulselessness confirmed by trained clinicians
- Pallor/cyanosis and sudden collapse
Investigations
Management
Lifestyle Modifications
- Activate emergency response immediately (999), use speakerphone, and start CPR without delay
- Community CPR and AED training to increase bystander response and early defibrillation
- Secondary prevention in survivors: smoking cessation, cardiovascular risk-factor optimisation, and adherence to cardiology follow-up
- Family screening where inherited sudden arrhythmic syndromes are suspected
Pharmacological Treatment
Vasopressor during adult ALS (non-bystander, trained clinicians)
- Adrenaline 1 mg IV/IO (10 mL of 1:10,000) every 3-5 minutes during cardiac arrest
Given as soon as possible for non-shockable rhythms; for shockable rhythms, typically after 3rd shock. Do not delay CPR/defibrillation to give drugs.
Antiarrhythmic for refractory shockable rhythm (adult ALS)
- Amiodarone 300 mg IV/IO after the 3rd shock, then 150 mg IV/IO after the 5th shock if VF/pulseless VT persists
- Lidocaine 1 mg/kg IV/IO (alternative if amiodarone unavailable/unsuitable), with additional dosing per ALS protocol
Use only in refractory VF/pVT. Monitor for hypotension/bradyarrhythmia after ROSC; specialist protocols apply.
Reversible-cause targeted therapy
- Naloxone 400 micrograms IV/IM, repeated every 2-3 minutes up to 10 mg in suspected opioid toxicity (primarily for respiratory depression; arrest management still prioritises CPR/ALS)
- Calcium chloride 10% 10 mL IV for life-threatening hyperkalaemia/hypocalcaemia or calcium-channel blocker toxicity (as cause-directed treatment)
Cause-specific drugs should not interrupt core resuscitation steps. Safety warning: medication delivery in arrest is for trained professionals; lay responders should focus on CPR and AED use.
Surgical / Interventional
- Immediate defibrillation with AED/manual defibrillator for shockable rhythms
- Advanced airway interventions by trained teams (for example supraglottic airway or endotracheal intubation)
- Urgent coronary angiography with possible PCI after ROSC when acute coronary occlusion is suspected
- Implantable cardioverter-defibrillator (ICD) consideration in selected survivors with ongoing arrhythmic risk
Complications
- Hypoxic-ischaemic brain injury and long-term cognitive impairment
- Recurrent arrhythmia or further cardiac arrest
- Acute kidney injury, hepatic injury, and multiorgan dysfunction after prolonged low-flow/no-flow states
- Aspiration pneumonia and acute lung injury
- Rib/sternal fractures from chest compressions
- Psychological sequelae in survivors and relatives (anxiety, depression, PTSD)
Prognosis
Overall survival from out-of-hospital cardiac arrest is poor, with fewer than 1 in 10 surviving to discharge in most series. Prognosis is strongly time-dependent: immediate bystander CPR can markedly improve survival, early defibrillation within minutes offers the best outcomes, and each minute of delay significantly worsens the chance of discharge alive. Initial rhythm also matters: VF/pulseless VT carries better survival than PEA/asystole, while older age and major comorbidity are adverse factors.
Sources & References
💊BNF Drug References(1)
- Ponesimod[cautions]
✅NICE Guidelines(1)
- Cardiac arrest - out of hospital care[overview]
📖Textbook References(20)
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 421)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 418)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 266)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1050)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 316)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 423, 424)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 267)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 267)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 398)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 229)[context]
- Guyton and Hall Textbook of Medical Physiology (John E. Hall, Michael E. Hall) (Z-Library).pdf(pp. 307)[context]
- Guyton and Hall Textbook of Medical Physiology (John E. Hall, Michael E. Hall) (Z-Library).pdf(pp. 307, 308)[context]
- Guyton and Hall Textbook of Medical Physiology (John E. Hall, Michael E. Hall) (Z-Library).pdf(pp. 387)[context]
- Oxford Handbook of Clinical Diagnosis (Huw Llewelyn, Hock Aun Ang, Keir Lewis etc.) (Z-Library).pdf(pp. 37)[context]
- Oxford Handbook of Clinical Diagnosis (Huw Llewelyn, Hock Aun Ang, Keir Lewis etc.) (Z-Library).pdf(pp. 497, 498)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 669, 670)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 863)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 7, 8)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 7, 8, 9)[context]
- [Williams, Bailey and Love's Short Practice of Surgery] Norman Williams, Christopher Bulstrode, P Ronan O'Connell - Bailey & Love's Short Practice of Surgery 26E (2013, CRC Press) - libgen.li.pdf(pp. 865, 866)[context]