Why the First Few Minutes Matter Most

Every year in the UK, tens of thousands of people collapse outside hospital after their heart stops beating properly. When that happens, the brain and vital organs are starved of oxygen, and survival falls by roughly ten per cent for every minute that passes without help. Bystander CPR buys precious time, but for certain rhythms — ventricular fibrillation and pulseless ventricular tachycardia — the only thing that will restart the heart is a defibrillator.

That is why automated external defibrillators, or AEDs, now hang in green cabinets outside village halls, leisure centres, railway stations, shopping centres and even old phone boxes. They are designed for people who have never used one before. The machine does the thinking: it analyses the heart rhythm, decides whether a shock is appropriate, and will not deliver one if it is not. It talks you through every step in clear, calm English.

Send for Help and Find the Machine

Before anything else, call 999 and put the phone on speaker so you can keep both hands free. Tell the call handler where you are and that someone is not breathing normally. They will stay on the line, talk you through CPR and tell you where the nearest defibrillator is — many ambulance services hold a database of them and can give you the cabinet code if one is needed.

If there is anyone else nearby, send them for the AED while you start chest compressions. Do not leave the casualty alone to fetch it yourself unless the cabinet is within sight and you can be back within seconds.

• Compress the centre of the chest hard and fast — around 5 to 6 cm deep, at 100 to 120 compressions per minute.
• If you are trained and willing, give two rescue breaths after every 30 compressions.
• Do not stop to check for a pulse. If they are unresponsive and not breathing normally, treat it as a cardiac arrest.

Open the Case and Listen to the Prompts

Switch the AED on as soon as it arrives — some models start automatically when you lift the lid. From that moment, simply do what the voice says. It is deliberately loud so it can be heard over a crowd, and it will repeat instructions if you need a moment. There is no way to do this in the wrong order; the machine will not let you.

Cut or tear clothing away from the chest so you have bare skin to work with. If the chest is wet with rain, sweat or water, dry it quickly with whatever you have — a towel, a shirt, a tea towel. If the casualty has a very hairy chest and the pads will not stick, most kits contain a small razor; shaving the two pad sites takes seconds and makes a real difference.

Pads on Bare, Dry Skin

Peel the backing from the pads and press them firmly onto the chest, following the pictures printed on them. One goes below the right collarbone, the other on the left side beneath the armpit. They need to be flat, stuck down and touching skin only.

• Move any medication patches, nicotine patches or jewellery out of the way — do not place a pad over them.
• Look and feel for a hard lump under the skin near the collarbone, which may be an implanted pacemaker or defibrillator. Keep the pad at least 8 cm clear of it.
• For a child under eight, use paediatric pads or the paediatric setting if the machine has one. If it does not, use the adult pads — a shock from an adult AED is far better than no shock at all.

Once the pads are on, the machine will tell everyone to stand clear while it analyses the rhythm. Keep your hands off the casualty and ask others to do the same.

Stand Clear During the Shock

If a shock is advised, the AED will charge and then instruct you to stand clear. Say the words out loud — "stand clear" — and check with your own eyes that nobody is touching the casualty, including you. Oxygen masks and any loose equipment should be moved away. Then press the flashing shock button if the machine asks you to.

The body may jolt or twitch. That is normal. As soon as the machine says so, go straight back into chest compressions. Do not pause to look for a pulse or wait for the person to wake up; the AED will re-analyse the rhythm every two minutes and tell you when to stop again. Keep going until the ambulance crew arrives, the casualty begins to breathe normally and move, or you are genuinely too exhausted to continue.

After the Shock: What Happens Next

Leave the pads on and keep the AED switched on. If the person starts breathing normally, roll them into the recovery position and stay with them, watching their breathing closely — they can deteriorate again. If that happens, start CPR and use the AED exactly as before. When the paramedics arrive, tell them how many shocks were delivered and how long you have been doing compressions.

Afterwards, it is worth letting the ambulance crew know which defibrillator you used so the pads and battery can be replaced, and it is worth telling someone how you are feeling. Using an AED is something thousands of ordinary people do every year, often with no training at all. If you would like to feel more confident, a short CPR and defibrillator course through a local community group takes only a couple of hours — and the best preparation of all is simply knowing where your nearest cabinet is before you ever need it.