A defibrillator, or an automated external defibrillator (AED), is a device designed to provide an electric shock to a person experiencing cardiac arrest. The purpose of the shock is to help the heart re-establish an effective rhythm that can sustain life. In the critical moments following a cardiac arrest, prompt and efficient use of an AED can significantly increase the chances of survival. The device is designed to be user-friendly, allowing even those with minimal training to use it effectively in an emergency.
It is important to recognise the signs of cardiac arrest, which include unresponsiveness and absence of normal breathing. When these signs are present, immediate action is critical. The use of an AED involves turning on the device, following the audio and visual prompts to attach the electrode pads correctly, and allowing the machine to analyse the heart’s rhythm. If a shockable rhythm is detected, the AED will advise the rescuer to deliver a shock.
Understanding the operation of an AED and its role in the chain of survival can empower individuals to act with confidence in an emergency. The accessibility of AEDs in public spaces and the provision of clear instructions makes it feasible for laypeople to become potential lifesavers. Through awareness and basic training, communities can improve their response to cardiac emergencies and potentially save lives.
Last reviewed: September 2026 — checked against Resuscitation Council UK Guidelines 2025.
Understanding Defibrillators
Defibrillators are critical life-saving tools designed to treat sudden cardiac arrest by restoring a normal heart rhythm through an electric shock. Their correct operation is paramount to increasing the chances of survival.
Types of Defibrillators
Automated External Defibrillators (AEDs) are portable, user-friendly devices available in public places. Used by laypeople, they guide users through the defibrillation process with voice prompts. Implantable Cardioverter-Defibrillators (ICDs) are surgically placed into patients at high risk of recurrent, potentially life-threatening arrhythmias, while Manual Defibrillators are primarily operated by healthcare professionals with the necessary expertise.
How Defibrillators Work
A defibrillator delivers an electric shock to the heart, with the goal of stopping nonproductive and dangerous fibrillation. By doing so, it allows the heart’s natural pacemaker to reset and potentially resume a normal rhythm. It’s a critical intervention during sudden cardiac arrest when the heart’s electrical activity becomes chaotic, preventing it from pumping blood effectively.
Automated External Defibrillators (AEDs) in the Community
AEDs in the community are invaluable. Potential rescuers can find them in locations such as shopping centres, airports, and leisure centres. The British Heart Foundation and NHS have worked to improve the availability of AEDs across communities, recognising their importance in bolstering survival rates from sudden cardiac arrest when immediate action is essential.
Importance of AEDs in Saving Lives
Rapid defibrillation is a key component of the chain of survival; therefore, AEDs are indispensable in their role in enhancing survival chances. Studies have shown that immediate defibrillation can significantly increase the likelihood of survival following sudden cardiac arrest, accentuating the critical nature of AED accessibility and training within communities to save lives.
Before Using a Defibrillator
Prior to utilising a defibrillator, it’s crucial to properly assess the emergency situation, determine the necessity for defibrillation, and ensure that emergency services are alerted. Additionally, understanding how to prepare the device for use and being mindful of legal considerations form part of the essential preliminary steps.
Assessing the Situation
Start with a primary survey. Check that it is safe to approach, then check for responsiveness by gently shaking the person’s shoulders and asking loudly whether they are alright. If they do not respond, they are unresponsive – and under the Resuscitation Council UK Guidelines 2025 that alone is enough to call 999 now, before you assess anything else. Only then do you open the airway with a head tilt and chin lift and spend up to ten seconds checking for normal breathing. Occasional gasps or slow, noisy breathing are not normal breathing; they are a sign of cardiac arrest. Do not feel for a pulse – lay rescuers are no longer taught to check one.
Calling for Help
It is paramount to call 999 as soon as you find that the person is unresponsive if you’re in the UK, and request emergency help. This is the change that catches most people out: you no longer wait until you have confirmed that their breathing is abnormal before phoning. If you are alone, place the call on speakerphone to ensure that you can continue to render aid whilst speaking with the emergency services. Ask a bystander to fetch the nearest defibrillator while you carry on – the ambulance call handler can tell you where it is, because UK ambulance services draw on the British Heart Foundation’s national defibrillator network, The Circuit. If you are on your own with no one to send, calling 999 and starting CPR come first.
When to Use a Defibrillator
A defibrillator should be used when an individual is unresponsive and not breathing normally. Signs that indicate the use of an Automated External Defibrillator (AED) include sudden collapse or an inability to respond. Attach the AED as soon as it arrives; if in doubt, use it, because the device analyses the rhythm itself and will not shock anyone who does not need it.
CPR and Defibrillation
If the individual is not breathing or only gasping, start CPR immediately. Give chest compressions in the centre of the chest to a depth of 5 to 6 cm at a rate of 100 to 120 per minute, with two rescue breaths after every 30 compressions if you are trained and willing. If you are not trained to give rescue breaths, or would rather not, give continuous chest compressions with no interruptions instead – hands-only CPR, which the Resuscitation Council UK recommends for exactly this situation. CPR should be continued until the defibrillator is ready to use or until emergency services take over.
Preparing the Defibrillator
When preparing an AED, turn on the device and follow its instructions. Most AEDs will guide you through the process, including where to place the pads. Ensure that no one is touching the person when delivering a shock.
Legal Considerations
In the UK, Good Samaritan laws typically protect individuals who assist others in distress. The use of AEDs by untrained bystanders is encouraged as the devices are designed to prevent a shock from being delivered if it’s not needed. It’s important, however, to be aware of and follow the guidelines provided by the NHS or relevant health authorities.
How to Use a Defibrillator
Using a defibrillator correctly can be critical in an emergency cardiac situation. Following the precise steps for operation and post-shock procedures is vital to improve the chances of survival.
Step-by-Step Guide
- Call 999: Call for emergency assistance as soon as you find the person unresponsive – before you check their breathing, and before you start using the device. Send someone else for the nearest AED while you stay with the casualty.
- Start CPR: If the individual is not breathing or not breathing normally, begin CPR immediately. Push hard and fast in the centre of the chest, 5 to 6 cm deep at 100 to 120 compressions per minute, giving two rescue breaths after every 30 compressions if you are trained and willing – otherwise compressions only.
- Turn on the AED: Power on the automated external defibrillator (AED) and follow the voice prompts.
- Attach Pads: Expose the individual’s chest and attach the defibrillator pads. One pad should be placed on the right upper chest, the other below the left breast. For more detail, see our guide to the proper placement of defib pads.
- Stand Clear & Analyse: Ensure that no one is touching the individual. Press the ‘analyse’ button if the AED does not automatically start analysing the heart rhythm.
- Deliver Shock: If the AED advises a shock, ensure everyone is clear and press the ‘shock’ button.
After Delivering a Shock
- Continue CPR: Immediately resume CPR after the shock is delivered for 2 minutes before the AED reanalyses.
- Repeat if Necessary: If a shock is recommended again, clear the area and press the shock button.
- Monitor Breathing: Check regularly for normal breathing. If the individual starts breathing normally, place them in the recovery position.
Troubleshooting Common Issues
- Device Not Turning On: Check for any visible issues with the AED battery and connections.
- No Shock Advised Message: Continue with CPR as the AED will only advise a shock if it detects a rhythm likely to respond to defibrillation.
- Residue or Medication Patches: Wipe the chest dry before attaching pads and remove any medication patches with gloves on.
Training on how to use a defibrillator is advised to be more effective in an emergency; however, AEDs are designed to be used by anyone, regardless of training, as they provide step-by-step instructions.
Post-Defibrillation
After a defibrillator has been used, it is crucial to monitor the patient’s vital signs continuously, prepare for the arrival of emergency services, and ensure the defibrillator is ready for future use. Emotional support for the patient and those involved in the incident shouldn’t be overlooked.
Monitoring the Patient
Once an automated external defibrillator (AED) has been used and the patient is stabilised, they should be monitored closely. Watch for signs of breathing, circulation, and any changes in consciousness. If the patient remains unresponsive but is breathing, place them in the recovery position while ensuring their airway remains open.
Handover to Emergency Services
When the emergency services arrive, a clear and concise handover is important. Inform them of the patient’s condition, the number of shocks administered, and any changes observed. It’s essential to share all relevant information to continue providing optimal care.
Reporting and Equipment Maintenance
After the mayhem has settled, any use of an AED should be reported to the local NHS ambulance service as this can be vital for the patient’s ongoing health record and provides valuable data for community health initiatives. The defibrillator should undergo a maintenance check to ensure it’s operational for future emergencies.
Emotional Support and Debriefing
Both the patient and the individuals involved in providing care may require emotional support and debriefing after such a stressful event. Liaising with the healthcare professionals can help understand what to do after the incident. This not only aids emotional recovery but ensures the community feels prepared and confident to save lives again in the future.
Additional Considerations
When using a defibrillator, it’s vital to understand not only the basic operation but also additional factors that can affect its use. These considerations include the device’s use on certain populations, training requirements, accessibility and placement, operating procedures for specific individuals, and the impact of a defibrillator on a community’s health readiness.
Defibrillator Use on Children and Infants
An AED should be attached as soon as possible to a child of any age, including an infant under one year. The Resuscitation Council UK Guidelines 2025 are explicit that you should never withhold defibrillation from a baby or a child because you only have a standard adult AED to hand. Activate the paediatric mode or attenuated paediatric pads if the device has them, for every infant and child under about 25 kg (roughly eight years old); for larger children and adolescents, and whenever the AED has no paediatric setting, use it in standard adult mode. Pad position also changes for the smallest casualties: in infants and children under about 25 kg, use the front-and-back (anteroposterior) position, with one pad on the middle of the chest just to the left of the breastbone and the other on the back between the shoulder blades. If you are on your own with a child, calling 999 and starting CPR take priority over going to fetch an AED.
Importance of Ongoing Training
Regular training in defibrillator use ensures prompt and correct application of AEDs during cardiac emergencies. The British Heart Foundation emphasises that ongoing training enhances muscle memory ensuring critical steps are followed correctly under pressure.
Defibrillator Accessibility in Workplaces
Workplaces should ensure AEDs are easily accessible and that staff are aware of their location. Periodic drills and signage can enhance awareness and accessibility. Additionally, the Resuscitation Council UK offers valuable information on incorporating defibrillators into emergency response plans.
Who Can Use a Defibrillator
AEDs are built for use by the general public, and one does not need to have medical training to use them. Clear instructions provided by the AED guide the user through the process. However, formal training can instil confidence to act quickly and correctly.
Defibrillators and Pacemakers
If the person in need has a pacemaker or an implantable cardioverter defibrillator, the Resuscitation Council UK advises placing the pad more than 8 cm away from the device, or using an alternative pad position such as front-and-back. A visible bulge under the skin, usually below the collarbone, typically indicates the device’s location, and care must be taken to avoid placing the pads directly over it. An implanted device is never a reason to withhold defibrillation.
Raising Community Awareness
Communities benefit from awareness programmes regarding the availability and use of defibrillators. They can partner with organisations like the British Heart Foundation to teach residents about AED locations and use, which in turn can increase survival rates from cardiac arrests.
Final Thoughts
Understanding the operation of an Automated External Defibrillator (AED) is crucial for providing aid during a sudden cardiac arrest. These devices are designed to be user-friendly and can guide a rescuer with clear, spoken instructions. It’s important to remember that an AED is most effective when used in conjunction with CPR (cardiopulmonary resuscitation).
In an emergency situation, the priority is to call emergency services immediately. If an AED is readily available, one should use it without hesitation; time is of the essence. The device will analyse the heart’s rhythm and, if necessary, advise the user to administer a shock. This could potentially save lives by restoring a normal heart rhythm.
- Do: Call for medical help immediately.
- Don’t: Delay using the AED while waiting for medical professionals.
AEDs are often found in public places, and their locations are sometimes registered with emergency services so that a 999 operator can direct bystanders to the nearest unit. The use of an AED by a bystander can increase the chances of survival until professional help arrives.
They are equipped with visual and verbal cues, ensuring that even individuals without formal training can operate them. However, it is encouraged to familiarise oneself with the use of an AED through first aid training.
- Remember: Quick action can make a significant difference.
Every second counts, and the assimilation of AEDs into emergency response routines has already had a profound impact on survival rates for sudden cardiac arrest victims. The presence of AEDs in communities, workplaces, and schools underscores the importance of public access to defibrillation as a critical step in saving lives.
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