Cardiac arrest

Overview

Arrest rhythms
FeatureVF / pVT (shockable)PEA / Asystole (non-shockable)
MechanismDisorganised/fast electrical activity - ineffective pumpPEA: organised ECG but no mechanical output; Asystole: no electrical activity
ECGVF: chaotic; pVT: wide-complex tachycardiaPEA: recognisable rhythm (e.g. sinus); Asystole: flat
DefibrillationYes - shock immediatelyNo - treat reversible cause
Key drugAdrenaline 1 mg IV after 3rd shock; amiodarone 300 mg IV after 3rd shockAdrenaline 1 mg IV as soon as IV access obtained, repeat every 3-5 min

Feature	VF / pVT (shockable)	PEA / Asystole (non-shockable)
Mechanism	Disorganised/fast electrical activity - ineffective pump	PEA: organised ECG but no mechanical output; Asystole: no electrical activity
ECG	VF: chaotic; pVT: wide-complex tachycardia	PEA: recognisable rhythm (e.g. sinus); Asystole: flat
Defibrillation	Yes - shock immediately	No - treat reversible cause
Key drug	Adrenaline 1 mg IV after 3rd shock; amiodarone 300 mg IV after 3rd shock	Adrenaline 1 mg IV as soon as IV access obtained, repeat every 3-5 min

🎯
PEA = organised ECG + no pulse. The problem is mechanical/metabolic, not electrical - defibrillation has no role. Always ask: what reversible cause is driving this?

Reversible Causes - 4Hs and 4Ts

4Hs and 4Ts (most important for PEA)
Hypoxia
Hypovolaemia
Hyperkalaemia / metabolic
Hypothermia
Tension pneumothorax - tracheal deviation, absent breath sounds
Tamponade - pericardial, no breath sound change
Thrombosis (PE) - RV dilatation on echo, post-op/immobility
Toxins

💡
Tension pneumothorax and massive PE are the two reversible causes most commonly tested. Both cause PEA via mechanical obstruction to cardiac output. Tension: tracheal deviation, absent breath sounds, mechanically ventilated patients at risk. PE: post-operative, immobile patient, RV dilatation on echo - treat with alteplase 50 mg IV and continue CPR for 90 minutes post-thrombolysis.

Management - ALS Algorithm

Step 1 - Confirm arrest
1Unresponsive, apnoeic (or agonal gasping), no central pulse
2Start CPR 30:2 immediately
3Attach defibrillator - identify rhythm
↓
Shockable (VF / pVT)
Deliver 1 shock → immediately resume CPR 2 min → rhythm check. After 3rd shock: adrenaline 1 mg IV + amiodarone 300 mg IV. Repeat adrenaline every 3-5 min. Amiodarone 150 mg after 5th shock. Alternative to amiodarone: lidocaine.
Non-shockable (PEA / Asystole)
CPR 2 min + adrenaline 1 mg IV as soon as IV access obtained → repeat every 3-5 min. Identify and treat reversible cause. No shock. No atropine.
↓
Special case
1Witnessed, monitored arrest (e.g. in ED): up to 3 successive shocks acceptable before starting CPR

⚠️
Adrenaline 1 mg IV (NOT 500 mcg - that is the IM anaphylaxis dose). Route must be IV or intraosseous during arrest - IM is not appropriate. Atropine is NO LONGER part of the ALS algorithm; it is reserved for symptomatic bradycardia only.

📌
Why adrenaline? Acts via alpha-1 receptors causing systemic vasoconstriction → increases aortic diastolic pressure → increases coronary perfusion pressure during CPR → improves chance of ROSC.

Post-ROSC Care

•Confirm ROSC - return of pulse, rise in end-tidal CO2, arterial waveform

•12-lead ECG immediately - if STEMI, refer urgently for PCI

•Oxygen - titrate to SpO2 94-98%; avoid hyperoxia

•Haemodynamic target - MAP >65 mmHg

•Temperature - avoid fever (>37.7°C); controlled normothermia

•Neurological prognostication - deferred to at least 72 hours post-ROSC