About This Page
This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- Cardiac arrest rhythms: shockable (VF, pulseless VT) vs non-shockable (PEA, asystole)
- BLS: 30 compressions : 2 breaths, rate 100–120/min, depth 5–6 cm. Attach AED as soon as available
- ALS: Shockable → defibrillate immediately, then CPR 2 min → rhythm check. Adrenaline 1 mg IV after 3rd shock, then every 3–5 min. Amiodarone 300 mg IV after 3rd shock, 150 mg after 5th
- ALS: Non-shockable → adrenaline 1 mg IV immediately, then every 3–5 min. NO defibrillation
- Reversible causes: 4 Hs (Hypoxia, Hypovolaemia, Hypo/Hyperkalaemia, Hypothermia) and 4 Ts (Tension pneumothorax, Tamponade, Toxins, Thrombosis PE/MI)
Overview
Cardiac arrest is the sudden cessation of effective cardiac mechanical activity, confirmed by the absence of a detectable pulse. Without immediate intervention, irreversible brain injury begins within 4–6 minutes. The chain of survival consists of early recognition, early CPR, early defibrillation, and early advanced life support with post-resuscitation care. Shockable rhythms (VF and pulseless VT) have a better prognosis than non-shockable rhythms (PEA and asystole). The Resuscitation Council UK 2021 guidelines provide the national standard for BLS and ALS algorithms.
Epidemiology
Out-of-hospital cardiac arrest (OHCA) affects approximately 30,000–60,000 people per year in the UK. Overall survival to hospital discharge is approximately 8–10%. Survival is highest for witnessed VF arrest with early bystander CPR and defibrillation (up to 50% in optimal settings). In-hospital cardiac arrest (IHCA) affects approximately 1 in 500 hospital admissions with survival to discharge around 20%. The most common initial rhythm in OHCA is VF/pulseless VT; in IHCA it is PEA or asystole.
Clinical Features
Symptoms
Sudden collapse with loss of consciousness
Preceding symptoms may include chest pain, palpitations, dyspnoea (not always present)
No response to stimulation
Signs
Unresponsive to voice and pain
Absent or abnormal breathing (agonal gasps are NOT normal breathing)
No palpable carotid pulse (healthcare professionals should check — lay rescuers need not)
Loss of consciousness, cyanosis, fixed dilated pupils (late signs)
Investigations
First-line
Cardiac rhythm assessmentAttach defibrillator pads/monitor immediately. Identify: VF, pulseless VT (shockable) vs PEA, asystole (non-shockable)
ABGAssess pH, K⁺, lactate, base excess — guide treatment of reversible causes
Second-line
Point-of-care bloodsGlucose, K⁺, Ca²⁺, Mg²⁺ — rapid identification of metabolic causes
Point-of-care ultrasoundDuring rhythm check — assess for tamponade, RV dilatation (PE), hypovolaemia, cardiac standstill
Specialist
12-lead ECG post-ROSCIdentify ST elevation → cardiac catheterisation, arrhythmia assessment
CT head and CT pulmonary angiographyIf cause of arrest unclear post-ROSC — exclude stroke, PE
Coronary angiographyIf STEMI on post-ROSC ECG → immediate PCI
Management
Resuscitation Council UK 2021 Guidelines1
Basic Life Support (BLS)
- Ensure scene safety. Check responsiveness (shake and shout). Call 999 and request AED
- Open airway (head tilt, chin lift). Look, listen, feel for normal breathing (max 10 seconds)
- If not breathing normally → start CPR: 30 compressions : 2 breaths
- Compressions: centre of chest, rate 100–120/min, depth 5–6 cm, allow full recoil, minimise interruptions
- Attach AED as soon as available — follow prompts
2
ALS — Shockable (VF / Pulseless VT)
- Defibrillate immediately (biphasic 150–200 J). Resume CPR for 2 min. Reassess rhythm
- If VF/pVT persists after 3rd shock: adrenaline 1 mg IV + amiodarone 300 mg IV
- Continue: shock → 2 min CPR → rhythm check. Adrenaline every 3–5 min (alternate cycles)
- After 5th shock: amiodarone 150 mg IV (further dose)
- Advanced airway (supraglottic or ETT) — then continuous compressions with 10 breaths/min
3
ALS — Non-shockable (PEA / Asystole)
- Adrenaline 1 mg IV immediately, then every 3–5 min
- CPR 2 min → rhythm check → continue
- NO defibrillation for asystole or PEA
- Actively seek and treat reversible causes (4Hs and 4Ts)
- Consider stopping if asystole persists despite 20 min of ALS and all reversible causes addressed
4
Post-resuscitation care (post-ROSC)
- Targeted temperature management (36°C for 24 h — NICE recommends avoiding fever)
- 12-lead ECG — if STEMI → immediate coronary angiography and PCI
- Aim SpO₂ 94–98%, avoid hyperoxia
- Aim normocapnia (PaCO₂ 4.5–6.0 kPa)
- Maintain MAP >65 mmHg (vasopressors if needed)
- ICU admission, neuroprognostication at ≥72 h post-ROSC
Complications
- Hypoxic brain injury: Leading cause of death post-cardiac arrest
- Post-cardiac arrest syndrome: Myocardial dysfunction, systemic inflammation, reperfusion injury
- Rib fractures: Common after CPR — acceptable consequence of effective compressions
- Aspiration pneumonia: From vomiting during resuscitation
- Organ failure: Multi-organ dysfunction from prolonged hypoperfusion
UKMLA Exam Tips
- 1Shockable rhythms (VF/pVT) → defibrillate FIRST. Non-shockable (PEA/asystole) → adrenaline FIRST
- 2Adrenaline timing: in shockable rhythms give after 3rd shock; in non-shockable give immediately
- 3Amiodarone is ONLY for shockable rhythms: 300 mg after 3rd shock, 150 mg after 5th shock
- 44Hs: Hypoxia, Hypovolaemia, Hypo/Hyperkalaemia and metabolic, Hypothermia. 4Ts: Tension pneumothorax, Tamponade, Toxins, Thrombosis (PE/MI)
- 5Agonal gasps are NOT normal breathing — start CPR immediately
- 6Compression rate: 100–120/min, depth: 5–6 cm — these numbers are commonly tested
- 7Post-ROSC: avoid hyperoxia (target SpO₂ 94–98%), perform 12-lead ECG immediately
practicetest your knowledge on cardiac arrest and bls/alsApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — cardiovascular and beyond.
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