Someone using a defibrillator (AED) as part of CPR, which you can learn in a St John Ambulance Cymru first aid at work training courses

Using a Defibrillator (AED)

Automated External Defibrillators (AEDs) are used to deliver a shock to a casualty who is in cardiac arrest. You can use an AED on your own or with a helper. 

You need to perform CPR as per current guidelines alongside the use of the AED. CPR is different for adults, children, and infants.



With a helper

Follow the steps below:

Step 1  

Once you have established the person is in cardiac arrest – send the helper to get the defibrillator and call 999/112. This will leave you free to begin CPR - remember to cover the face and do not give rescue breaths.

When the helper returns with a defibrillator, ask them to switch it on and take the pads out while you continue with CPR. They should remove or cut through clothing to get to the casualty's bare chest. They also need to wipe away any sweat. 

The defibrillator will give voice prompts on what to do. 

They should attach the pads to the casualty’s chest by removing the backing paper. Applying the pads in the positions shown on the device. 

  1. The first pad should be on the upper right side below the collar bone. 
  2. The second pad should be on the casualty’s left side below the arm pit. 
Note:
  • If the casualty is a child between the age of 1 and 8, the pads are placed differently. Place one pad in the middle of the chest and the other on the back between the shoulder blades. You should ideally use paediatric pads, but if these aren't available then adult pads can be used in the paediatric position.
  • If the casualty is an infant under the age of 1 then guidance on the use of an AED should be sought from the 999 call operator.
Step 2 

The defibrillator will analyse the heart's rhythm. Stop CPR, and make sure no one is touching the casualty. It will then give a series of visual and verbal prompts that should be followed. 

If the defibrillator tells you that a shock is needed, tell people to stand back. The defibrillator will tell you when to press the shock button. After the shock has been given, the defibrillator will tell you to continue CPR for two minutes before it re-analyses. 

If the defibrillator tells you that no shock is needed, continue CPR for two minutes before the defibrillator re-analyses. 

Step 3 

If the casualty shows signs of becoming responsive such as coughing, opening their eyes, speaking, or starts to breathe normally, put them in the recovery position. 

Leave the defibrillator attached. Monitor their level of response and prepare to give CPR again if necessary. 



Without a Helper

Should you be in a situation where someone has gone into cardiac arrest and there is a defibrillator available then you can use it without needing a bystander to help you. What is important to remember is that you do not leave the casualty to find a defibrillator. Once you have dialled 999/112 for an ambulance, a defibrillator will be coming with the ambulance.  

Step 1  

Before beginning CPR you will need to place the defibrillator on the casualty. To do this follow these simple instructions: 

Switch the AED - the defibrillator will give voice prompts on what to do. 

Remove or cut through clothing to get to the casualty's bare chest and wipe away any sweat. 

Attach the pads to the casualty’s chest by removing the backing paper. Applying the pads in the positions shown on the device 

  1. The first pad should be on the upper right side below the collar bone. 
  2. The second pad should be on the casualty’s left side below the arm pit. 
Step 2 

The defibrillator will analyse the heart's rhythm. Make sure no one is touching the casualty. It will then give a series of visual and verbal prompts that should be followed. 

If the defibrillator tells you that a shock is needed, tell people to stand back. The defibrillator will tell you when to press the shock button. After the shock has been given, the defibrillator will tell you to continue CPR for two minutes before it re-analyses. 

If the defibrillator tells you that no shock is needed, continue CPR for two minutes before the defibrillator re-analyses. 

Step 3 

If the casualty shows signs of becoming responsive such as coughing, opening their eyes, speaking, or starts to breathe normally, put them in the recovery position. 

Leave the defibrillator attached. Monitor their level of response and prepare to give CPR again if necessary. 

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