SN4 SHORT NOTE 5M ★ High-yield

Write a short note on Defibrillation.

General Surgery · Final Professional

Definition & Indication

Defibrillation delivers a controlled electric shock across the heart to depolarise the myocardium simultaneously, terminating a chaotic rhythm and allowing the sinus node to resume a coordinated beat. It is the definitive treatment for the shockable arrest rhythms — ventricular fibrillation (VF) and pulseless ventricular tachycardia (VT).

Key Points

Early defibrillation is a key link in the chain of survival — the sooner a shockable rhythm is defibrillated, the better the outcome. Shocks are delivered with minimal interruption to CPR (compressions resumed immediately after the shock). It is useless in asystole and is not used for pea. Safety: ensure everyone is clear of the patient and oxygen is moved away before discharging. Automated external defibrillators (AEDs) analyse the rhythm and guide lay/first responders.

DANGER / REMEMBER

Defibrillate only VF and pulseless VT — shocking asystole is ineffective and interrupts CPR. Ensure the area is clear and oxygen is removed before the shock, and resume compressions immediately afterwards.

CLINICAL PEARL

Defibrillation treats VF and pulseless VT only; earlier is better. Minimise CPR interruption, stay clear of the patient, and resume compressions at once after the shock. Not for asystole/pea.

Manual Versus Automated Defibrillators

Two kinds of defibrillator are used: the manual defibrillator, operated by a trained clinician who interprets the rhythm and decides whether to shock, is used within the advanced-life-support setting; the automated external defibrillator analyses the rhythm itself and instructs the operator whether a shock is advised, making it safe for lay rescuers and first responders and enabling the early defibrillation that so strongly improves survival. The widespread placement of automated defibrillators in public places, and their simplicity of use, are a deliberate strategy to shorten the time from collapse to the first shock in an out-of-hospital arrest.

CLINICAL PEARL

Defibrillate only VF and pulseless VT, as early as possible, keeping the pause in compressions to a minimum and standing clear with oxygen removed — and resume CPR immediately after the shock without waiting to reassess.

Resume compressions at once — do not pause to check rhythm.

Aspect	Detail
Shockable rhythms	Ventricular fibrillation, pulseless VT
Non-shockable	Asystole, pulseless electrical activity
Biphasic energy (adult)	120–200 J
Paediatric	4 J/kg
After shock	Resume compressions immediately for 2 minutes

KEY POINT

Key points TO remember

Defibrillation: synchronous depolarisation of the myocardium to terminate a chaotic rhythm.
Definitive treatment for shockable rhythms — VF & pulseless VT (not asystole/pea).
Early defibrillation improves survival (chain of survival); minimise CPR interruption.
Safety: everyone clear, oxygen away; resume compressions immediately after the shock.

EXAM TIP

Sources: Morgan & Mikhail’s Clinical Anesthesiology; Miller’s Anesthesia; Ajay Yadav’s Short Textbook of Anaesthesia; Resuscitation Council guidelines.

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