A complete guide to AED defibrillators training, use and their operation


Automatic external defibrillators (AEDs) are a vital piece of equipment that anyone can use to save the life of someone who has experienced a sudden cardiac arrest. They are becoming much more common in work places as part of first aid training and more accessible in public spaces across the UK.  If used promptly and correctly, they can significantly increase the chances of survival, especially when used in conjunction with cardio pulmonary resuscitation (CPR). However, not everyone knows how to use one. Here is our helpful guide to AED defibrillators training, use and operation.

Do I need an AED Defibrillator ?

As a general rule we would advise that any organisation; school, charity, construction site, hotel, office, manufacturing site. If they have the ability to buy an AED defibrillator we would recommend it would be a sound investment for the welfare of their staff, visitors and customers. Irrespective of any risk assessment process which takes place, even if the likelihood of a person having a sudden cardiac event is extremely small in your organisation, the most likely outcome if quick access to a defibrillator is not available, is the casualty not surviving.

It is not a legal requirement to perform a risk assessment for purchasing an AED defibrillator, but it is regarded as good practice.

Should my company install an AED?

To decide whether or not you need an AED, you need to look at the potential risk of a cardiac arrest on your premises. According to the Resuscitation Council article ‘Do I need an AED?’ all organisations need ‘to take precautions to reduce foreseeable risks’, including ‘considering the risk of a cardiac arrest occurring in the workplace’.

How to Perform an AED Risk Assessment

The level of risk is assessed by determining the chances of a sudden cardiac arrest, and multiplying this by the potential severity of the outcome. The likelihood is worked out on a scale of 1-5 by considering several factors, such as:

  • The volume of people present or visiting the premises (the greater the number of people, the greater the risk)
  • The age of these people (older people are at an increased risk of SCA)
  • The type of location (busy, stressful locations, such as airports are more likely to produce the circumstances for a SCA)
  •  Do you work in a multi occupancy building with quick access to an AED defibrillator

In this risk assessment, the severity of the outcome is indisputable, since the patient will invariably die if they are not treated promptly, so it is always 5. This means that most locations will be either a moderate risk (5-9) or a high risk (10-15), with high stress locations and locations with a predominantly elderly population creating an extreme risk (16 or more).

Acting on your risk assessment

In an ideal world, an AED should be installed immediately, wherever there is any risk whatsoever of a SCA. However, this is not always practically or financially possible. If you cannot install an AED immediately, then:

  • If you identify a moderate risk, you should aim to install an AED within the next financial year.
  • If you identify a high risk, you should aim to install an AED as quickly as reasonably possible.
  • If you identify an extreme risk, you should install an AED without delay.

What is a sudden cardiac arrest?

The heart is a muscle that pumps blood around the body and to and from the lungs. It creates its own electrical impulses to trigger the muscle contractions in a regular sequence, known as normal sinus rhythm.

During a sudden cardiac arrest (SCA), this rhythm is interrupted and the heart begins to act in a chaotic way, which is unable to pump the blood properly. This is most commonly due to an irregular rhythm, known as ventricular fibrillation (VF), but can also be caused by a rhythm that is too fast, known as ventricular tachycardia (VT) or too slow, known as bradycardia.


The British Heart Foundation estimates that around 80,000 SCAs occur in the UK every year, with three quarters of these occurring outside of the hospital environment where prompt, professional help would be available. It is estimated that the Ambulance Service in England attempts 25,000 resuscitations every year, but only a few of these patients survive.


Sudden cardiac arrest should not be confused with a heart attack, as this is a different condition entirely. During a heart attack, or myocardial infarction, the blood vessels supplying the heart muscles become blocked and this restricts their ability to pump the blood. A heart attack may cause a sudden cardiac arrest, if the area that triggers electrical impulses is damaged, but often heart attack victims remain conscious with a normal heart rhythm.

Sudden cardiac arrest is predominantly caused by heart disease and the resulting heart attack, but may also be caused by electrocution, drowning, choking, respiratory arrest and trauma. Occasionally, there is no identifiable cause for a SCA.


How does the AED help?

An AED is basically a portable version of the ‘crash cart’ that you see in hospitals or carried by ambulance staff. Instead of the paddles used on these machines, an AED has sticky electrodes to transmit the shock to the heart.

When the heart rhythm has been disrupted, an AED can be used to shock the heart back into a normal rhythm. This works by essentially stopping the heart’s electrical impulses, allowing the cells to recharge properly and restart in a normal rhythm. It has been describes as a similar process to re-booting your computer by turning it off when it gets stuck, and turning it back on to start afresh.

Despite what you often see in the movies and on TV, an AED cannot ‘jump start’ a heart that has stopped completely. This is called asystole, and would show up as a flat line on a heart monitor as there is no electrical activity in the heart. Asystole is known as a non-shockable rhythm.


The Chain of Survival

The problem in most cases of SCA is that the ambulance service simply cannot attend fast enough to make a difference. If defibrillation is applied within the first three to five minutes, survival rates can be as high as 75%, however the chances of survival drop by 7%-10% for every minute of delay after this. Even if you live or work close to an ambulance station, three to five minutes is an almost impossible deadline for the paramedics. With an AED on hand, however, defibrillation can easily be applied within this window.

To increase the chances of survival, first responders must apply what is known as the chain of survival. This involves:

Step 1: Early recognition– recognising someone is in cardiac arrest as quickly as possible. Often people who are having a heart attack will show symptoms before they collapse, and you should call for help as soon as you suspect there is a problem.

Step2:Calling an ambulance– summoning professional help without delay. Ideally this should be done by someone else while you look after the patient

Step 3: Performing basic CPR– chest compressions will not only keep blood flowing to the brain, but also keep the heart in a shockable rhythm so that the AED may be used.

Step 4:Using an AED– theAED should be used as soon as possible. You should get someone else to fetch it for you so that you can continue CPR.

If the chain of survival is followed, then the chances of a positive outcome increase significantly.


If you are faced with a sudden cardiac arrest, should you go to get the AED or start CPR?

It is important to understand that an AED is not a substitute for CPR. The Resuscitation Council recommend early, uninterrupted chest compressions to maintain blood flow to the brain and other vital organs. Early and continued CPR has been shown to more than double the chances of surviving a sudden cardiac arrest. CPR should be done in the ratio of thirty chest compressions to two breaths.

However, as discussed above, every second counts in a sudden cardiac arrest, and the use of an AED will be most effective if it is applied within three to five minutes. Therefore if you have help, you should start CPR immediately while someone else goes to fetch the AED machine, but if you are on your own, the AED machine must be your priority.

CPR should be continued throughout the chain of survival, and only stopped when absolutely necessary for the AED machine to monitor heart rhythm or apply a shock. If you have help, you should continue with CPR while the AED machine is prepared and the electrodes are attached to the victim. Unless otherwise instructed by the AED machine, you should continue CPR in between shocks, or until the ambulance crew or paramedics arrive.


Using an AED

  • What do I do? – All automated emergency defibrillators are designed to walk you through the process, so just follow the simple, clear instructions delivered by the machine using either voice commands or clear pictures and written instructions.
  • How do I prepare the victim? – You may need to cut away clothing to get to the bare chest, and if your kit contains a razor, you can quickly shave the two contact points to gain a better adhesion of the electrodes. If the victim is wet or sweating, you should dry the areas to help the pads to stick.
  • Where do I put the electrodes? – Diagrams on the pads will tell you where to place the electrodes, and the machine will check that they are placed correctly. One electrode should be placed on the chest, to the right of the heart just below the collarbone, with the second electrode placed below the heart on the left chest wall.
  • What f I get them mixed up? – Although the electrodes are labelled left and right, don’t worry if you get them the wrong way around; the AED will still work. Swapping them over will only waste time and there is a risk that the electrodes will not stick as well the second time.
  • What happens then? – The machine will check the heart rhythm. It is important to stop CPR while this happens and not touch the victim, as the machine may pick up your heart rhythm instead. If you have helpers, you should clearly tell them to “stop CPR and hands off”.
  • What if a shock is needed? – Semi-automatic emergency defibrillators will then inform you if a shock is required and you will need to press a button to deliver the shock. Fully-automatic emergency defibrillators will deliver the shock automatically. In either case, the machine will give you plenty of warning and once again you should tell any helpers to “stay clear” as the shock is administered.
  • What if I get it wrong? – You should not be concerned about pressing the button, as the machine will not allow you to administer a shock if it is not needed. You cannot get it wrong and there is no chance that you can harm the victim or stop a normal rhythm by applying a shock in error.
  • Remember CPR – It is vital to continue with CPR in between shocks and rhythm tests, in order to maintain a shockable rhythm in the heart. If you allow the heart to run out of oxygen, it may stop completely and you will not be able to save the victim using the AED.


  • When should I stop? –You should follow the machine’s instructions until emergency help arrives, or the victim shows signs of recovery, such as coming round, coughing, opening their eyes and moving. It is important to check that they are breathing normally. Do not remove the electrode pads from the victim, even if they seem to have improved, as their condition can change again very quickly and you may need to restart treatment.


AED safety

AEDs are designed to be as quick and easy to operate as possible, and you should simply follow the instructions that the machine gives you. However, there are a few additional safety considerations that you should be aware of:

  • Avoid jewellery – pads should not be placed on or near jewellery as this may conduct the current and cause burns to the skin.
  • Remove medical patches – some patches worn by heart patients, such as glyceryl tri- nitrate, may react to an electrical current and so you should remove any obvious patches just to be sure.
  • Dry wet skin – to ensure that the electrodes make good contact, you should dry the area before application. (However, there is no risk of you getting a shock from a wet victim, as the current travels between the two pads and not to ‘earth’.)
  • Keep the victim still – the AED can only analyse the heart rhythm if the victim is still, so it is important to stop CPR when instructed and switch off any vibrating machinery nearby. You should not use an AED on a fitting patient.


Maintaining an AED

An AED machine should be stored in a place that is readily accessible by both staff and the general public. It should never be locked away or stored in a manager’s office that may not be accessible if the manager is absent.

It should be stored with a rescue pack containing accessories that may be needed for use, such as scissors to remove clothing, a razor to shave hair and a towel or absorbent pads to dry the skin. Spare electrode pads should also be kept with the machine, in case the original pads do not stick properly, and paediatric pads should also be kept if the machine is installed in places where there are lots of children or children who are at rick of SCA.

The electrodes should be replaced every two years to ensure the adhesive remains effective, and the battery should be replaced regularly as indicated by the machine. Most AED machines will perform self-checks to monitor battery levels, software status and general functions, and will indicate when a problem is detected. You should check your AED regularly and put right any problems as soon as possible so that it is always ready for use in an emergency.




Do you need AED training?

Although specialist AED training is available, and AED use is covered in all one day emergency first aid at work and three day first aid at work courses, it is important to remember that anyone can used an AED to save a life. If there is no trained person available at the time of the incident, it is better to use the machine as an untrained operative, than to not use it at all. Here is what the experts have to say on the subject:

  • Resuscitation Council guidance
  • The Resuscitation Council states that ‘the use of AEDs should NOT be restricted to trained personnel’. Their published guidance says that although it is ‘highly desirable’ for people using an AED to have been trained in their use, there are often situations where no trained operative is present. Their advice is that ‘under these circumstances no inhibitions should be placed on any person willing to use an AED’.
  • HSE guidance
  • The HSE agrees with the Resuscitation Council that AED equipment ‘is safe to use and can be readily used by untrained bystanders’. However, they also ‘welcome the presence of awareness training in first aid courses, as it instils greater confidence in the use of AEDs’. The HSE guidance on defibrillator training goes on to say that ‘if your needs assessment identifies an AED need then we recommend your staff should be fully trained in its use’.
  • British Heart Foundation guidance
  • The British Heart Foundation recommend signage ‘designed to reduce the fear of using the defibrillator and encourage more people to use a defibrillator in an emergency’. Their downloadable Defibrillator / Heart Restarter sign clearly states that ‘anyone can use it, no training necessary’.


The benefits of training

As mentioned above, time is of the essence in an SCA situation, and literally every second counts. So having trained personnel, who are familiar with the AED equipment and know how to use it, can shave vital minutes off the time it takes to apply the required shock.

Training will make the operator more confident and competent, and crucially faster, in the use of the AED machine, and this will make their intervention more efficient and effective. Trained personnel are also more likely to step in straight away, where others may be more reluctant to get involved, once again saving vital minutes.

There are three levels of competence for AED operators.

  • Untrained operator
    1. If you have no training at all, you will still be able to operate the machine in an emergency situation. Automatic external defibrillators are designed to be as easy as possibleto use, and the machine will walk the untrained user step by step through the process using both auditory and visual cues. Some AED machines will deliver the shock automatically, while others require the operator to trigger the shock via a button. The equipment monitors the heart rhythm and will only deliver a shock if it is medically needed.
  • Awareness trained operator
    1. All One Day Emergency First Aid at Work courses, and Three Day First Aid at Work courses will cover the essentials of AED use. This is called AED Awareness Training and is aimed at familiarising the candidate with the machine and its operation.
  • Fully trained operator
  1. Separate AED Training courses will cover both the condition of sudden cardiac arrest and the use of machine in depth including:
  • The anatomy and physiology of heart conditions
  • Treatment of an unconscious casualty
  • How to open an airway and check for breathing
  • How to perform CPR on a non breathing casualty
  • How to check and maintain an AED machine
  • What to checkbefore using an AED
  • How to use an AED

This two hour training course gives the candidate a comprehensive overview of the machine and its use. This course is aimed at appointed first aiders and should be considered as part of the risk assessment for any company or organisation which is installing AED equipment.

This training can be delivered in-house, allowing staff to practice the techniques within the actual environment in which they will be used, making the training more relevant and effective.

Regular refresher training

A cardiac arrest is a very stressful situation, especially when it involves a close colleague or friend, and it is only natural that even the best-trained people will struggle and perhaps panic under such pressure. This is why regular AED training is recommended, and regular drills should be performed within the organisation, so that the appropriate reactions become second nature for nominated first aiders.

AED – a summary

While this article has covered automated emergency defibrillators in considerable depth, it is important to remember that they are designed to be as simple as possible, and that anybody can use one to save a life as part of the chain of survival. Just remember the four steps:

  • Spot the symptoms of sudden cardiac arrest
  • Call an ambulance
  • Apply CPR
  • Use the AED as instructed

Just by following these simple steps, three out of every four victims of sudden cardiac arrest could be saved.

Automated External Defibrillator – Frequently Asked Questions

 Some of the following questions are often asked to our instructors on First aid and AED courses. Some of them have been answered above, but we have tried to group them together to make them easily accessible.

What is an automated external defibrillator?

An automated external defibrillator (AED) is a device used in an emergency situation to restore normal heart rhythm after a sudden cardiac arrest. Sudden cardiac arrest will usually be fatal unless treatment is given promptly.

What is a sudden cardiac arrest?

A sudden cardiac arrest (SCA) occurs when the heart loses its normal rhythm and cannot pump the blood effectively. This is different to a heart attack, which occurs when blood vessels to the heart become blocked.

Can A Defibrillator Restart A Stopped Heart?

Contrary to popular belief, a defibrillator cannot restart the heart once it has stopped completely (flat-lined), but it can shock an abnormal rhythm back into a normal one.

How do I recognise a sudden cardiac arrest?

In a sudden cardiac arrest, the patient will normally be unresponsive and will not be breathing normally. By contrast, if the patient is having a heart attack, they will usually be conscious and responsive, even though they are in pain. An AED cannot help a heart attack patient.

How does a defibrillator work?

The AED checks for what is called a shockable rhythm in the heart. If it detects one, it will give an automatic electric shock, which momentarily stops the heart and allows it to reset to its normal rhythm.

The machine does this automatically, and most machines will administer the shock without operator input, however with some machines, you will be prompted to press a button to administer the shock.

When should I use an AED?

You should use an AED whenever you suspect someone is having a sudden cardiac arrest (ie they are unresponsive and nor breathing normally). It will only work if the patient needs it so you should not hesitate to use it.

Can I make things worse by using an AED?

Absolutely not. The system will check the condition of the patient and will only operate if it can help. You cannot shock a healthy patient and you cannot cause any harm by using the machine. However, if you don’t use it, the patient could die.

How quickly should the AED be used?

The AED should be used as soon as possible, as the chances of survival fall away rapidly with every minute that passes. After three minutes, there is a 70% chance of survival, but this drops to just 50% after five minutes and a mere 20% after eight minutes.

What should I do first in a cardiac arrest?

The first priority is to get someone to call the emergency services. You should then use the AED as quickly as possible. If there are people around to help, get them to retrieve the AED while you start CPR. If not, retrieve the AED as quickly as possible yourself.

Do I need to be trained to use an AED?

As the name suggests, the AED is an automated machine that can be used by anyone, with or without formal training. The machine will walk you, step by step, through the procedure with simple audio or on-screen instructions. You should never let a lack of training stop you from using an AED. Remember, you cannot do any harm, but you could save a life.