AED — Automated External Defibrillator Guide

An Automated External Defibrillator (AED) is a portable, battery-powered device that analyses a patient's heart rhythm and delivers an electrical shock when it detects a shockable arrhythmia — specifically ventricular fibrillation (VF) or pulseless ventricular tachycardia (pVT). These two rhythms cause the vast majority of sudden cardiac arrests in adults. Without defibrillation, the heart cannot resume an organised pumping rhythm on its own. CPR buys time, but the AED is what saves the heart.

Understanding how and when to use an AED is one of the most impactful first-aid skills any person can develop. The device is deliberately designed so that no medical training is required to operate it safely.

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Why AEDs Save Lives — The Time Factor

Survival from sudden cardiac arrest depends almost entirely on how quickly a shockable rhythm is treated. The statistics are stark:

• Defibrillation within 3–5 minutes of witnessed VF arrest: survival rate up to 70%
• Each minute of delay without defibrillation: approximately 10% reduction in survival probability
• After 10 minutes without defibrillation: survival is rare, even with CPR

CPR alone cannot convert VF or pVT back to a normal rhythm. What CPR does is circulate oxygenated blood to the brain and heart muscle, preserving the window of opportunity for defibrillation to succeed. Together, high-quality CPR and early defibrillation form the core of the Chain of Survival.

⚠️ Every minute matters. If an AED is nearby, retrieving and using it takes priority alongside calling emergency services. Do not wait for paramedics to arrive before attempting defibrillation.

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Recognising Sudden Cardiac Arrest

Before using an AED, you must confirm you are dealing with cardiac arrest, not a faint, seizure, or other emergency:

1. Check for response — tap shoulders firmly, shout "Are you okay?"
2. Call for help — shout for bystanders, send someone to call emergency services and retrieve the AED simultaneously
3. Check breathing — look at the chest for no more than 10 seconds. Agonal breathing (occasional gasping, gurgling) is NOT normal breathing — treat as cardiac arrest
4. No pulse check required — untrained rescuers should not waste time attempting a pulse check; assume cardiac arrest if unresponsive and not breathing normally

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Finding an AED

Public AEDs are increasingly common. Look for them in:

• Shopping centres, supermarkets, and transport hubs
• Gyms, sports facilities, and stadiums
• Airports and railway stations
• Government buildings, courthouses, and libraries
• Schools, universities, and workplaces
• Hotels and large entertainment venues

Apps and registries to find nearby AEDs:

• The Restart a Heart / GoodSAM app (UK) — shows nearest registered AED
• PulsePoint (USA) — crowd-sourced AED map plus community responder alerts
• Many local ambulance services maintain national AED registries

When calling emergency services, the dispatcher can often direct you to the nearest registered AED and may be able to remotely guide you through CPR and AED use.

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How an AED Works

An AED contains electrodes (pads) that sense the electrical activity of the heart. Its internal algorithm analyses the rhythm and determines whether a shock is appropriate. If a shockable rhythm (VF or pVT) is detected, the device charges and instructs you to deliver a shock. If the rhythm is non-shockable (asystole, pulseless electrical activity), it will NOT advise a shock — it is physically impossible to deliver an inappropriate shock with an AED.

This means you cannot make the wrong decision. The AED makes the clinical call. Your job is to attach it correctly, follow its instructions, and keep everyone clear during analysis and shock delivery.

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Step-by-Step AED Use

1. Turn on the AED — open the lid or press the power button. Most devices power on automatically when opened.
2. Follow voice prompts — all AEDs provide step-by-step spoken (and often visual) instructions. Do exactly what it says.
3. Expose the chest — remove or cut away clothing. A wet chest must be dried with a cloth or clothing before pad placement.
4. Attach the pads — peel the backing from the adhesive pads and place them as shown in the diagram on the pads themselves (and below).
5. Clear for analysis — ensure no one is touching the patient. Say loudly: "Stand clear." The AED analyses the rhythm.
6. Deliver shock if instructed — press the shock button when told. Ensure no one touches the patient at this moment.
7. Immediately resume CPR — after the shock, begin chest compressions without waiting to check for a pulse. The AED will prompt you.
8. Continue cycles — the AED will re-analyse every 2 minutes. Follow prompts until emergency services arrive.

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Pad Placement

Correct pad placement is critical for the shock to pass through the heart muscle effectively.

Pad	Position
Right (sternum)	Upper right chest, just below the right collarbone
Left (apex)	Left side of chest, below and to the left of the left nipple — mid-axillary line

Most AED pads have diagrams printed directly on them. If a second set of pads is included (some devices), they can be placed in an anterior-posterior configuration (one pad on the front of the chest, one on the back) if the standard position is impractical.

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Special Situations

Wet Victim

Water conducts electricity and reduces the effectiveness of the shock while creating a risk of injury to bystanders. Quickly dry the chest with a cloth, clothing, or jacket before applying pads. If the patient is lying in a puddle, move them to a dry surface if safe to do so.

Child (Under 8 Years / Under 25 kg)

Use paediatric AED pads if available — they deliver a reduced energy dose appropriate for a child's smaller heart. If only adult pads are available, use them rather than withholding defibrillation. In this case, place one pad on the front of the chest and one on the back (anterior-posterior placement) to prevent pad overlap.

Implanted Pacemaker or ICD

A visible lump under the skin (usually below the collarbone, left or right) indicates an implanted device. Do not place pads directly over the device. Position the pad at least 8 cm (3 inches) away. The AED can still be used effectively.

Medication Patch

Remove any medication patch (nitroglycerin, nicotine, pain patch) from the chest before applying AED pads. Wear gloves if available. Leaving a patch in place may cause burns or reduce shock effectiveness.

Hairy Chest

Excessive chest hair can prevent good pad adhesion. If the AED is equipped with a razor (some kits include one), quickly shave the pad areas. If not, press the pads down firmly — a firm press-and-rip can also remove hair quickly as a last resort.

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Common Fears — Addressed

Fear	Reality
"I might shock someone who doesn't need it"	Impossible — the AED will NOT advise a shock unless a shockable rhythm is detected
"I might hurt the patient by doing it wrong"	The patient is in cardiac arrest — doing nothing guarantees death; AEDs are designed for untrained users
"I'll be sued if something goes wrong"	Most countries have Good Samaritan laws protecting lay rescuers acting in good faith
"The shock will kill someone nearby"	Only the person touching the patient during shock delivery is at risk — clear the area and it is safe
"I don't know how"	The device talks you through every step; no memorisation is needed

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AED Maintenance and Readiness

If you manage an AED at a workplace, community centre, or school:

• Inspect monthly — check indicator light shows "ready" status
• Check battery level — replace per manufacturer schedule (typically 2–5 years)
• Check pad expiry — pads have a use-by date printed on the packaging (typically 2 years)
• Register your AED — register with your local ambulance service so dispatchers can direct bystanders to it
• Post-use — after any use, replace pads and notify your maintenance provider

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Quick Reference

Situation	Action
Patient unresponsive, not breathing	Call emergency services, start CPR, retrieve AED
AED arrives — when to use	As soon as it is available — prioritise over continued CPR if alone
Shockable rhythm detected	Stand clear, press shock button, immediately resume CPR
No shock advised	Continue CPR; AED will re-analyse in 2 minutes
Wet chest	Dry chest before applying pads
Child under 8	Use paediatric pads if available; anterior-posterior if not
Pacemaker visible	Place pads at least 8 cm away from device
After shock	Do NOT check pulse — resume compressions immediately
When to stop	When EMS take over, patient recovers, or you are physically unable to continue

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Key Takeaways

• AEDs save lives — survival rates up to 70% with defibrillation in the first 3–5 minutes
• The device is designed for untrained users — it will not shock unless the rhythm requires it
• Register any AED you manage with your local ambulance service
• AED + high-quality CPR together give the best chance of survival
• Familiarise yourself with the location of AEDs in your workplace and regular venues before an emergency occurs