All about defibrillators (AEDs) - what they are and how to use them


Cardiac arrests can affect anyone at any time. 30,000 occur outside of hospitals across the UK each year. Currently less than 10% of these people experiencing cardiac arrests in the community survive…

With speedy emergency treatment, chances of survival shoot up by a whopping 80%.

CPR and AED shocks given within the first four minutes are crucial to enable survival.

Yet, terrifyingly, the average ambulance response time in an urban area is a full eleven minutes. In the rest of the UK, it’s around 8 minutes.

20% of out-of-hospital cardiac arrests happen in public places. If you suffer an arrest out and about, you would be reliant on the public’s ability to perform CPR and indeed the availability of a defibrillator.

CPR alone can double the chances of survival. When you use a defibrillator in addition to quality CPR, the odds of someone’s survival can jump from around 6% to 74% – an incredible difference.


What are AEDs?

Defibrillators are the brightly coloured boxes seen in supermarkets, tube, rail and bus stations, airports, some telephone boxes and other high traffic areas and public places.

All about defibrillators – what they are and how to use them



How a defibrillator works:

An AED is an Automatic External Defibrillator – which means that it automatically detects if someone is in a shockable rhythm and it speaks to you, to tell you what to do.

Defibrillators do not jump start the heart like jump starting a car; they stop it like rebooting a computer. Ultimately this allows the individual heart cells to recharge simultaneously and the pacemaker in the heart to hopefully restart it in a normal rhythm. 

The defibrillator administers a shock to stop the heart if it is in an abnormal but shockable rhythm. Enabling the heart’s own system to reboot and hopefully restart in sinus rhythm (normal beat).

AEDs are used in addition to CPR to save the lives of those suffering cardiac arrest.

Research has shown that deploying a defibrillator within 3–5 minutes of collapse can produce survival rates as high as 50–70%.


Where to find them

Automatic External Defibrillators (AEDs) are now easily accessible at numerous locations; train and tube stations, shopping centres, Dental and GP Practices, sports grounds, leisure centres and are available for the general public to use.

They can be semi-automatic (you still need to press the shock button when indicated) or fully automatic (the machine shocks automatically when a shock is advised).


Apps can help locate AEDs

These days there are apps that can be used to locate your nearest defibrillator, such as HeartStart, Pulse Point AED and Good Sam. Good Sam can locate nearest first responders to help too.


Why are they important?

Defibrillators are crucial to be able to have a chance of bringing someone back following a cardiac arrest. CPR helps circulate the blood, keeping the heart and brain sufficiently oxygenated. The AED is necessary to deliver the shock hopefully returning the heart to a viable rhythm.

Most sudden cardiac arrests result from ventricular fibrillation (VF). VF is a fast and erratic heart rhythm originating in the heart’s ventricles.

AEDs are only indicated for use if someone is unconscious and not breathing normally. An AED will only enable a shock to be given if someone is in a shockable rhythm – Ventricular Fibrillation or Ventricular Tachycardia, the machine will recognise the rhythm and advise whether or not a shock is advised.

Most importantly: you cannot shock someone if they don’t need it.


Chain of survival

All about defibrillators – what they are and how to use them


The sooner you recognise there is a problem, get help on the way, start CPR, use a defibrillator and transfer the casualty to advanced medical care, the better the outcome.

Law change

The Defibrillators Availability Bill was first read in Parliament in 2018 and not only recognises the need for AEDs in public places but also legislates for awareness and training to ensure people are ready to use them.
Since September 2020, CPR has become a mandatory topic on the National Curriculum in England. Consequently, all young people in England should have learnt how to give CPR and use a defibrillator by the time they leave secondary school. Hopefully this will dramatically improve our survival rates from out of hospital cardiac arrests, to the same extent as it has in Denmark and other Scandinavian countries.


Click here for an online Condensed Emergency First Aid at Work – with Covid-19 updates


What do Employers need to know?

It is not compulsory for employers to purchase AEDs to comply with the Health and Safety (First Aid) regulations 1981. However, if your needs assessment identifies an AED need then it is recommended that staff should be fully trained in its use.


How to use an AED

Hundreds of people are alive today entirely due to the prompt and appropriate use of a defibrillator. For every minute’s delay in deploying a defibrillator, the odds of survival reduce by about 10%.

Once activated, the AED will talk to you and tell you what to do: 

Check for:
Danger: Do not put yourself in danger
Response: If no response shout for help and if possible, get a bystander to call for an ambulance and locate a defibrillator if there is one.
Airway: Open the airway and check for breathing.
Breathing: If the casualty does not appear to be breathing normally and there are less than 2 breaths in a 10 second period you will need to start CPR
If you are on your own: Call 999/112 and get the AED as quickly as possible if there is one nearby.
If you have help: Get your bystander to let the emergency services know that the casualty is unconscious and not breathing. Meanwhile, you should bring the AED as quickly as possible. Continue CPR whilst waiting for the defibrillator.


Giving effective CPR

To give effective CPR: push down 5-6 cms on the centre of the chest at a rate of about 2 compressions per second and ensure a release from pressure in between compressions, to enable the heart to refill. Give 30 compressions to 2 breaths.

Giving CPR during the pandemic: Because of the heightened awareness of the possibility that the victim may have COVID-19, Resuscitation Council UK offers this advice:

  • Recognise cardiac arrest by looking for the absence of signs of life and the absence of normal breathing. Do not listen or feel for breathing by placing your ear and cheek close to the patient’s mouth. If you are in any doubt about confirming cardiac arrest, start chest compressions until help arrives.
  • Make sure an ambulance is on its way. If COVID 19 is suspected, tell them when you call 999.
  • If there is a perceived risk of infection, rescuers should place a cloth/towel over the victims mouth and nose and attempt compression only CPR and early defibrillation until the ambulance (or advanced care team) arrives. Put hands together in the middle of the chest and push hard and fast.
  • Early use of a defibrillator significantly increases the person’s chances of survival and does not increase risk of infection.
  • If the rescuer has access to personal protective equipment (PPE) (e.g. FFP3 face mask, disposable gloves, eye protection), these should be worn.
  • After performing compression-only CPR, all rescuers should wash their hands thoroughly with soap and water; alcohol-based hand gel is a convenient alternative. They should also seek advice from the NHS 111 coronavirus advice service or medical adviser.


Defibrillators are designed to be as easy as possible to use. They will tell you how to use them so even if you’ve never been trained you should try your hardest.

All about defibrillators – what they are and how to use them


1. Firstly, activate it. Machines vary but this is usually done by opening the lid or pressing an obvious button.
2. If you aren’t alone, someone should continue CPR, whilst the other attaches the leads to the AED (if necessary).
3. Dry the chest (and use the razor to shave if excessively hairy).

4. Peel the pad off the backing one at a time and place onto the dry chest according to the diagram on the packet.

5. Place one pad below the casualty’s right collar bone.
6. Position the other on the casualty’s left-hand side, over their lower ribs.
7. The AED will analyse the heart rhythm.
8. Stop CPR when instructed by the AED.
9. Ensure no one is touching the casualty.

If a shock is advised:

10. Check the whole length of the casualty to ensure no one is touching them.
11. Then shout loudly: ‘stand clear’.
12. Press the flashing shock button as directed (fully automated AEDs will do this automatically once a shock is advised).
13. Continue with CPR as directed.
14. Keep going with 30 compressions to 2 breaths.
15. Do not stop to check them unless they begin to regain consciousness and start breathing normally.
16. The machine will reassess their heart rhythm every 2 minutes and advise another shock if indicated.

If no shock is advised:

• Continue with CPR and follow prompts
• Keep going until help arrives. Stop CPR if the casualty begins to regain consciousness and starts to breathe normally.
• The machine will reassess their heart rhythm every 2 minutes and advise a shock if indicated.

To give CPR: 30 compressions, then 2 rescue breaths. Repeat.

If there is more than one rescuer swap every couple of minutes.

Defibrillators dramatically improve a casualty’s chance of survival and are now widely available for the general public to use. However, we need far more in the community and work-places to be able to have the major improvements on survival from cardiac arrest that is seen in other countries such as Sweden.


Common myths about defibrillators and AEDs

Unfortunately there are many common misconceptions about defibrillators that prevent people from incorporating them in their mainstream first aid equipment:

“Defibrillators are complicated!” – MYTH

They couldn’t be much easier! The machine speaks to you and takes you step by step through what you need to do to help save someone’s life. Furthermore, they are now available in so many public places and are easily accessible for the general public to grab and use as quickly as possible in a medical emergency. Additionally, you do not need specific training to use them.

“You have to be medically trained to use them!” – MYTH

Wrong! They are available for use by the general public. Ideally you would have received training in how to give the best CPR as this will make a huge difference and give them the best possible chance of survival. Using an AED is simple.

“You are jump starting the heart, like you do with a car!” – MYTH

Quite the reverse from jump-starting the heart, you are stopping the heart to allow the heart’s natural back-up system to take over and return it to normal sinus rhythm. Speed is of the essence as research has shown that the chances of survival for an out of hospital (community) cardiac arrest are only about 6%.

Thankfully, if you can get the pads onto the patient’s chest within 3 minutes and they are in a shockable rhythm, the chances of survival jump to 74%. This drops by 10% for every minute’s delay in using the machine.

“You could make things worse!” – MYTH

You cannot use a defibrillator if the casualty does not need it! It will not let you. So apply the pads, switch on the machine, you simply can’t do anything wrong. If someone is unconscious and not breathing, if you don’t do anything they will die.

“A defibrillator will always bring them back to life!” – MYTH

Sadly, this is not the case. There are many reasons why someone may experience a sudden cardiac arrest and it is not possible to resuscitate everyone. However, good quality CPR, prompt use of a defibrillator and swift transfer to professional medical care, will give them the best possible chance.

“You need to wait until the heart has stopped before using the machine!” – MYTH

Definitely not the case. The sooner you use the defibrillator the better their chances of survival.

“They are expensive!” – MYTH

You can now get a good quality defibrillator from us for less than £650.

“You can’t use them on children” – MYTH

If a child is unconscious and not breathing, you should use a defibrillator as quickly as possible in the same way as you would with an adult. You can use adult pads if you don’t have children’s ones available and would place one on the front of the chest and one on their back. For a child you start with 5 rescue breaths.

“You don’t need to do CPR if you are using a defibrillator” – MYTH

It is essential to be giving effective CPR alongside using the defibrillator. CPR circulates blood to the heart and brain. Without quality CPR it is highly unlikely the casualty will survive.

“Paramedics will always be there before I need to use it!” – MYTH

I am afraid that this is highly unlikely as our emergency services are hugely overstretched and they are not likely to be with you within 3 minutes.


Click here for an online Condensed Emergency First Aid at Work – with Covid-19 updates


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