I’ve Got the Defibrillator… Now What?
When I teach first aid courses, one question comes up time and time again, read on for a complete Step-by-Step Guide to using an AED.
“I’ve attached the defibrillator pads and given the first shock… what happens next?”
It’s a great question, and one that many people are unsure about.
People often imagine that a defibrillator (AED – Automated External Defibrillator) gives one shock and then the casualty suddenly wakes up. Films and television don’t help, often showing dramatic recoveries that simply aren’t how cardiac arrests happen in real life.
The reality is that an AED is there to guide you throughout the entire resuscitation. It doesn’t just deliver a shock and stop working. It continues to analyse the casualty’s heart rhythm, tells you exactly what to do next and supports you until the ambulance crew arrives.
The good news is that modern AEDs are incredibly clever. They are designed to be used by ordinary members of the public, not just healthcare professionals. You don’t need to remember complicated medical procedures because the machine talks you through every step. You don’t need to be first aid trained to use a defibrillator.
In this blog, we’ll look at exactly what happens from the moment the defibrillator arrives, what happens after the first shock, what “No Shock Advised” really means, and answer some of the most common questions I’m asked by learners.
First things first – don’t panic
If someone has collapsed and is in cardiac arrest, every second counts.
Hopefully someone has already called 999 and another person has gone to collect the nearest defibrillator.
As soon as the AED arrives, don’t be frightened by it.
You cannot accidentally make the situation worse by following its instructions.
Modern AEDs are specifically designed so that they will not allow you to deliver a shock unless it is needed. The machine analyses the casualty’s heart rhythm before deciding whether a shock is appropriate.
If a shock isn’t required, it simply won’t let you give one.
This is why AEDs are so safe to use.
Continue CPR while someone prepares the AED
If there are two or more rescuers, don’t stop CPR while someone opens the AED.
One person should continue chest compressions while another:
- Opens the case.
- Switches the machine on.
- Removes the pads.
- Prepares the casualty’s chest.
Keeping interruptions to CPR as short as possible gives the casualty the best chance of survival.
If you’re on your own, quickly turn the AED on and follow the voice prompts.
Turn the AED on immediately
Most defibrillators either switch on automatically when you lift the lid or have a large power button.
As soon as it’s switched on, the machine begins giving clear spoken instructions.
Don’t try to work ahead.
Listen carefully and follow each prompt in order.
The AED has been designed to guide you step by step.
Prepare the casualty’s chest
The AED pads need to stick directly to the skin.
Remove or cut away clothing covering the chest.
Before applying the pads, quickly check for anything that might prevent them sticking properly.
If the chest is wet
Dry it quickly with a towel, clothing or anything absorbent.
Water can reduce the effectiveness of the pads.
If there is excessive chest hair
Most AED kits contain a razor.
Only shave the area where the pads need to stick, and only if the hair prevents good contact.
Don’t waste valuable time shaving the entire chest.
If the casualty has medication patches
If a patch is exactly where the pad needs to be placed, remove it while wearing gloves if available and wipe the area before applying the pad.
Jewellery
Necklaces usually don’t need removing unless they interfere with pad placement.
Attach the pads
Most adult pads have pictures showing exactly where they go.
Normally:
- One pad is placed on the upper right side of the chest, just below the collarbone.
- The second pad is placed on the left-hand side of the chest, below the armpit.
Take a moment to smooth the pads down firmly so they stick properly.
Don’t worry if they aren’t absolutely perfect.
Getting them on quickly is more important than spending time trying to make them look neat.
Stand clear while the AED analyses
Once the pads are attached, the AED will tell everyone to stand clear.
At this point:
- Stop CPR.
- Make sure nobody is touching the casualty.
- Clearly say:
“Stand clear!”
The AED now analyses the heart rhythm.
This only takes a few seconds.
Touching the casualty during analysis could affect the reading.
Shock advised
If the AED detects a heart rhythm that can be treated with electricity, it will announce:
“Shock advised.”
The machine will usually charge automatically.
Some AEDs require you to press a flashing shock button.
Others deliver the shock automatically after a countdown.
Before the shock is delivered:
- Check that nobody is touching the casualty.
- Look around the casualty.
- Clearly say:
“Stand clear!”
Once everyone is clear, allow the shock to be delivered.
You may notice the casualty’s body jerk slightly.
This is completely normal.
What happens after the first shock?
This is the question I probably hear more than any other during first aid training.
Many people think they should now:
- Check for a pulse.
- See if the casualty is breathing.
- Wait to see if they wake up.
The answer is no.
As soon as the shock has been delivered, the AED will tell you to restart CPR immediately.
This is one of the most important parts of the whole resuscitation process.
Don’t wait.
Don’t pause.
Don’t spend time looking for signs of improvement unless the casualty is obviously moving, breathing normally or showing clear signs of life.
Instead:
Resume chest compressions immediately.
Continue CPR until the AED tells you to stop again.
Why do we restart CPR straight away?
Many people are surprised by this.
Surely if the shock has worked, shouldn’t we stop?
Not necessarily.
A defibrillator doesn’t restart the heart like pressing a reset button on a computer.
Instead, the electrical shock attempts to stop the abnormal rhythm that is preventing the heart from pumping effectively.
The hope is that the heart’s own natural pacemaker can then regain control.
However, even if this happens, the heart often needs help.
Chest compressions continue circulating oxygen around the body while the heart recovers.
Stopping CPR too early could reduce the casualty’s chance of survival.
The AED keeps working
The first shock isn’t the end of the process.
The AED continues guiding you.
Typically, you’ll perform around two minutes of CPR before the machine says something like:
“Stop CPR. Analysing heart rhythm.”
Everyone stands clear again.
The AED checks the heart rhythm.
It then makes another decision.
Either:
- Shock advised
or
- No shock advised
The cycle continues until the ambulance crew arrive or the casualty shows clear signs of life.
What if the AED says “No Shock Advised”?
This often confuses people.
Some think it means the casualty is recovering.
Unfortunately, this isn’t always the case.
“No Shock Advised” simply means that the heart rhythm present is not one that will benefit from a defibrillation shock.
It does not necessarily mean the heart has started beating normally.
If the casualty is still unresponsive and not breathing normally:
Continue CPR immediately.
Leave the pads attached.
Keep following the AED instructions.
The machine will continue checking the heart rhythm at regular intervals.
Sometimes a rhythm changes and a shock becomes appropriate later.
When do I stop CPR?
Continue until one of the following happens:
- The casualty starts breathing normally and shows obvious signs of life.
- The ambulance crew tell you to stop.
- You become physically unable to continue.
- The situation becomes unsafe.
If another trained person is available, swap every two minutes if possible, as chest compressions are physically demanding.
When the ambulance arrives
When the ambulance crew take over, don’t remove the pads.
Leave everything exactly as it is unless instructed otherwise.
Tell the crew:
- Approximately what time the casualty collapsed.
- When CPR started.
- When the AED was attached.
- How many shocks were delivered (if you know).
- Whether the casualty ever showed any signs of life.
- Any medical information you know.
The AED stores important information about the incident.
Paramedics may download this data later to help guide ongoing treatment.
What happens to the AED afterwards?
Many people never think about this.
Once the incident has finished, the AED needs checking before it can be used again.
Usually this involves:
- Replacing the pads (they are single use).
- Checking or replacing the battery if required.
- Cleaning the unit.
- Inspecting cables.
- Running the machine’s self-test.
- Returning it to its cabinet ready for the next emergency.
If the AED belongs to your workplace, school or organisation, make sure the responsible person knows it has been used.
If there is no person you can hand it over to. Put it back in the cabinet, as the authorised person will know it is out of circuit and can go over the checks. Once the AED is fully checked and in full working order, the authorised person will put the AED as available with Circuit, and is ready to be used again.
Don’t forget about yourself
Helping during a cardiac arrest can be emotionally overwhelming.
Many rescuers replay events in their minds afterwards and wonder if they did enough.
Remember:
You gave someone the best possible chance of survival.
Without early CPR and early defibrillation, survival rates are much lower.
Even if the outcome wasn’t what everyone hoped for, your actions mattered.
If you’re struggling afterwards, speak to your employer, family, friends or seek professional support if needed.
Final thoughts
The biggest thing I want people to remember is this:
You don’t have to remember every step.
That’s the job of the AED.
It talks to you.
It tells you when to stop.
It tells you when to continue.
It tells you whether to shock.
It tells you when to restart CPR.
Your role is simply to stay calm, follow the prompts and keep going until help arrives.
You are never expected to be perfect.
Doing something is almost always better than doing nothing.
If you’ve never used a defibrillator before, I would encourage you to attend a practical first aid course. Having the opportunity to practise using an AED on a training manikin can make all the difference if you ever need to use one in a real emergency.
Frequently Asked Questions My Learners Ask
Can I accidentally shock someone who doesn’t need it?
No. The AED analyses the heart rhythm and will only advise a shock if one is appropriate.
What if I press the shock button by mistake?
If the AED hasn’t advised a shock, it won’t allow one to be delivered.
Can I stop CPR after the first shock?
No. Restart CPR immediately unless the casualty is showing obvious signs of life.
What if the casualty moves after the shock?
If they begin breathing normally or show clear signs of life, follow the AED prompts and monitor them. If they remain unresponsive and are not breathing normally, continue CPR.
What if the AED keeps saying “No Shock Advised”?
Continue CPR and follow every prompt. The machine will reassess the heart rhythm regularly.
Should I remove the pads when the ambulance arrives?
No. Leave the pads attached unless a healthcare professional tells you otherwise.
Can I use a defibrillator on a child?
Yes. If available, use paediatric pads for children under eight years old. If paediatric pads aren’t available in an emergency, adult pads may be used, following current guidance and ensuring they don’t touch each other.
What if the casualty has a pacemaker?
Avoid placing the pad directly over the visible pacemaker lump. Position it slightly away from the device.
Can I use an AED on someone who is pregnant?
Yes. A cardiac arrest is a life-threatening emergency, and an AED should be used in the same way.
What if the casualty is lying on a wet surface?
Move them to a safer area if it can be done quickly. Dry the chest before applying the pads and make sure nobody is touching the casualty when a shock is delivered.
What if there is chest hair?
Only shave enough hair to allow the pads to stick properly if necessary. Don’t delay treatment unnecessarily.
What if I don’t know how long they’ve been unconscious?
Start CPR, use the AED and tell the ambulance crew everything you do know. Don’t delay treatment trying to work it out.
Will I get into trouble if I use a defibrillator?
People acting in good faith to help during an emergency are extremely unlikely to face legal action. The priority is giving the casualty the best possible chance of survival.
Does the AED remember what happened?
Yes. Most AEDs record information such as heart rhythms, timings and shocks delivered. This data can help healthcare professionals.
What if I’m on my own?
Call 999, put your phone on speaker if possible, start CPR and use the AED as soon as it arrives. The emergency call handler can also provide guidance until help arrives.
Our current first aid courses – A Complete Step-by-Step Guide to Using an AED;
Our Emergency and First Aid at Work courses are for those working in an office, factory, warehouse, manufacturing or on a building site. These courses will set you up to know exactly what to do in an emergency. Completing our courses will help you understand the hazards and risks in your workplace to therefore prevent accidents.
Apprentices, staff who are unlikely to be left alone with children, and lunchtime supervisors are all candidates for our Emergency Paediatric First Aid Training. Our one-day course includes roles and responsibilities of a first aider, first aid kits, accident reporting, reasons of a life-threatening condition, CPR, defibrillator, causes of unconsciousness and recovery position, choking, bleeding, burns, and minor injuries.
Our Paediatric First Aid Training 2-day course includes all elements of the one-day first course including; broken bones, spinal injuries, head injuries, slings, sprains and strains, diabetes, febrile convulsions, hypothermia, hyperthermia, epilepsy, poisons, eye injuries, allergies and anaphylaxis, and asthma.
This course is ideal for those working alone with children, whether you are a Teacher or Teaching Assistant working in the Early Years or a childminder. Our Paediatric courses are fully accredited. We have open courses running at our Brownhills Centre or we can come to your setting.
Additionally, if you prefer to have a short session with us and complete a bespoke parents/grandparents course; our Parent’s first aid course is for you. These start from 2 hours up to 4 hours. Can include any modules of your choice, but we will cover: reasons of life-threatening conditions, CPR, Defibrillator, unconsciousness, recovery, choking and gagging, burns, and minor illnesses, including dangers within the home.
Our courses provide you with the peace of mind that you’ll know what to do in the event of an emergency, such as illnesses like asthma. Furthermore, getting first aid training will give you the skill set of knowing exactly what to do if your child, friend, or work colleague suffers from an injury or life-threatening condition. Never put yourself in a situation where you’re thinking, “Because Emergencies Don’t Only Happen at Work” Get First Aid Trained Today!
If you have any questions about this blog, we are happy to help. A Complete Step-by-Step Guide to Using an AED – if you want to know how, book onto an annual first aid course with us. Here is the link to our upcoming courses. https://www.hmbtrainingservices.co.uk/courses
For further enquiries, please call us on: 01543 453338 or email on info@hmbtrainingservices.co.uk
