Cardiac Arrest and Advanced Life Support
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Direct answer
Cardiac arrest is the cessation of effective cardiac output, recognised by an absent pulse and unresponsiveness. Advanced life support divides it into shockable rhythms, ventricular fibrillation and pulseless ventricular tachycardia, and non-shockable rhythms, asystole and pulseless electrical activity. High quality compressions and prompt defibrillation for shockable rhythms come first, adrenaline is given every three to five minutes, and the search for reversible causes runs throughout.
What you must remember
- Compressions: 100 to 120 per minute, depth 5 to 6 cm in adults, full chest recoil and minimal pauses; rhythm check every two minutes.
- Shockable rhythms: ventricular fibrillation and pulseless VT get an immediate shock, followed by two minutes of CPR before the next check.
- Adrenaline: 1 mg every three to five minutes, given after the second shock in shockable rhythms and as early as possible in asystole or PEA.
- Amiodarone: 300 mg after the third shock, with a further 150 mg if needed; lidocaine is an acceptable alternative.
- 4H (5H in AHA): hypoxia, hypovolaemia, hypo- or hyperkalaemia and metabolic disturbance, and hypo- or hyperthermia; the AHA list also names hydrogen ion acidosis separately.
- 4T: tension pneumothorax, cardiac tamponade, toxins and thrombosis, whether coronary or pulmonary.
- Confirmation: waveform capnography; a sudden sustained rise in end-tidal CO2 suggests return of circulation.
- Post-ROSC care: 12-lead ECG for STEMI and PCI, avoidance of hypotension and hyperoxia, and targeted temperature management per current guidance.
Running the algorithm for a collapsed patient
A 58-year-old man collapses in a hospital corridor, and the nurse finds no pulse. CPR starts at once, and the first rhythm check shows fine ventricular fibrillation.
- Confirm and call: The team confirms arrest, calls for help and starts compressions at 100 to 120 per minute with minimal pauses.
- Shock immediately: The defibrillator is attached and a shock is delivered immediately. Two minutes of CPR follow, with the airway secured and waveform capnography checking ventilation.
- Check the rhythm: The next rhythm check determines the path. If the rhythm remains shockable, adrenaline follows the second shock and amiodarone follows the third.
- Treat non-shockable rhythms: If the rhythm is asystole or pulseless electrical activity, adrenaline is given as early as possible and no shock is delivered.
- Hunt the cause: At every check the team asks what is driving the arrest. A hypovolaemic patient needs fluid and blood, a tension pneumothorax needs decompression, and a pulmonary embolus may call for thrombolysis under expert guidance.
- Start the post-ROSC bundle: Once circulation returns, the work shifts to ECG, oxygen titrated to avoid hyperoxia, blood pressure support and temperature control.
Where the algorithm breaks down
Four traps recur in examiner questions.
- Trap: shocking a non-shockable rhythm, or delaying the shock while adrenaline is given to a fibrillating patient Correct: the shock is the treatment for ventricular fibrillation, and adrenaline does not replace it.
- Trap: giving atropine routinely in asystole or PEA Correct: atropine is not routinely recommended for these rhythms, so a stem offering it as the answer is testing current guidance.
- Trap: missing the underlying cause Correct: a patient after a long flight with sudden hypoxia points to pulmonary embolism, a patient with a fractured rib and falling pressures points to tension pneumothorax, and sudden hypotension after cardiac surgery raises tamponade.
- Trap: adding drugs after circulation returns Correct: a patient who regains circulation but remains hypotensive or febrile is at risk of a worse neurological outcome, so blood pressure support and temperature control usually come before more drugs.
Frequently asked questions
What is the defibrillation energy in adult cardiac arrest?
Biphasic defibrillators deliver energy specified by the manufacturer, typically 120 to 200 J, while older monophasic machines deliver 360 J. The device labelling should be followed for the exact setting.
When is adrenaline given in cardiac arrest?
Adrenaline 1 mg intravenously is given every three to five minutes. In shockable rhythms it follows the second shock, and in asystole or PEA it is given as early as possible.
What are the 4H and 4T causes of cardiac arrest?
The 4H causes are hypoxia, hypovolaemia, hypo- or hyperkalaemia with metabolic disturbance, and hypo- or hyperthermia; the AHA lists hydrogen ion acidosis as a fifth H. The 4T causes are tension pneumothorax, cardiac tamponade, toxins and thrombosis, whether coronary or pulmonary.
Why is capnography used during cardiac arrest?
Waveform capnography confirms endotracheal tube placement and reflects the quality of CPR. A sudden sustained rise in end-tidal CO2 suggests return of spontaneous circulation, while a persistently low reading during CPR prompts a check of compression quality.
What is the first drug for shock-refractory ventricular fibrillation?
Amiodarone 300 mg intravenously is given after the third shock for shock-refractory ventricular fibrillation or pulseless VT, followed by 150 mg if needed. Lidocaine is an acceptable alternative when amiodarone is unavailable.