Everything you need to know about using a defibrillator

As every state school gets one, here’s what you need to know about the lifesaving device. By Imy Brighty-Potts.

Imy Brighty-Potts
Tuesday 25 July 2023 13:13 BST
AEDs are now in every state-funded school (Alamy/PA)
AEDs are now in every state-funded school (Alamy/PA)

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Louise Thomas

Louise Thomas


In a huge step for first aid in the UK, more than 20,000 defibrillators – which are devices that give an electric shock to the heart of a person who is in cardiac arrest – have been delivered to state schools across the country since January.

Cardiac arrest can affect anyone, of any age, but according to St John Ambulance research, when a defibrillator is used within the first three minutes of a cardiac arrest, the chances of survival increase by up to 70%.

Knowing how a defibrillator works could save someone’s life, but what should you know before using one?

What is a defibrillator?

“A defibrillator is an electrical device that provides a shot across the heart to help bring people out of cardiac arrest,” explains James McNulty-Ackroyd, head of clinical projects and paramedic at St John Ambulance.

They are often labelled as an AED which is “an automated external defibrillator, and it recognises when using one would be beneficial for the patient. When we talk about cardiac arrests, we talk about shockable and non-shockable, and an AED is useful when the heart is in particular shockable rhythms”, he says.

When used, the electrical shock stuns the heart to send it back to its normal function “from the right shoulder down to the left armpit”.

The AED knows when it should work after the pads have been applied, because it “recognises the rhythm like an ECG automatically, and it will not shock if the heart is not in one of the relevant rhythms”.

When should you use one?

You only need a defibrillator in an incident of cardiac arrest.

“They should only be used when the patient is not breathing normally, or the heart has stopped,” explains McNulty-Ackroyd. “Their breathing may be like a fish out of water, there is no rhythm to it, there is no real air entry, or non-purposeful gasping.

“The heart is not pumping in that situation – it is not working, but there is some movement. They need a defibrillator and high-quality CPR (cardiopulmonary resuscitation).”

What should you be wary of?

The good news is, there’s not much to worry about when using one.

“Ideally, you should not have anyone touching the patient when you press the big red button, but there are lots of different devices on the market and most have written and audible instructions, and tell you what to do, so it will say to stand clear and tell you what to press and when,” he explains.

You need to take or cut the person’s shirt off, though.

“There is quite a lot of disinformation about taking someone’s bra off. If you do not take their bra off, you cannot get the pads in the right place. Cut down the middle of the bra, and let it fall open.”

What do you actually do?

So, you have seen someone go into cardiac arrest or found someone who has collapsed. What do you do?

“If you find someone who you think is in cardiac arrest, start CPR, shout for someone to bring you a defibrillator, and ask them to call for help,” advises McNulty-Ackroyd.

“The first thing the ambulance service will ask is, ‘Are they breathing?’ They will ask if they’re awake and you will say ‘no’, as they are in cardiac arrest.

“An ambulance will be sent as the highest priority in that area. In the meantime, you should be using an AED and performing CPR.

“When you ring 999, they will tell you how to do CPR. Do not worry about hurting someone you are doing CPR on. That person is dead, they cannot feel pain, if they sit up and go ouch, they are not in cardiac arrest.”

When using the defibrillator, “the first pad goes on the upper right, touching the clavicle [bone of the pectoral arch], and the other into the left armpit, nice and high”, he explains.

Every minute you don’t shock that abnormal rhythm, the person loses a chance of life, so use a defibrillator and perform CPR if you are in any way worried about someone who has collapsed.

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