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Defibrillator: how it works!

by Josephine Andrews
Published: Last Updated on 270 views

A defibrillator is designed to restore the heart’s natural rhythm when someone has life-threatening arrhythmias. To do this, the device emits electric shocks via electrodes on the chest of the person concerned. Automated external defibrillators (AEDs) are used in first aid. They are designed in such a way that even a layman can operate them. Find out here when and how a defibrillator should be used and what needs to be considered during defibrillation.

quick overview

  • What is a defibrillator? A device that delivers electrical shocks via electrodes to bring an abnormal heart rhythm (such as ventricular fibrillation) back into its natural rhythm.
  • Use of the defibrillator: Stick on the electrodes according to the instructions, then follow the (voice) instructions of the device.
  • In which cases? The AED should be connected whenever a person becomes suddenly unresponsive and not breathing normally. The device then decides whether a shock delivery is required.
  • Risks : Danger for first responders and victims due to current flow in combination with (a lot of) water. Singing of chest hair when very dense.


  • When defibrillating, follow the device (AED)’s voice or written/graphic instructions closely. Then you can’t do anything wrong, even as a layman.
  • If there is a second first aider on site next to you, one will get the defibrillator and the other will start with manual resuscitation (resuscitation). If you are alone, you must begin chest compressions immediately. If anyone else comes along, ask them to look for a defibrillator.
  • Do not use the defibrillator in water or standing in a puddle.
  • Do not attach defibrillator pads (also called “paddles”) directly above a pacemaker (often recognizable by a scar or similar in the chest area) or another medical implant. The electrical impulse can be impaired in such places.
  • Do not touch the patient while the device is analyzing the patient’s heart rhythm or delivering electrical shocks. The device will prompt you accordingly.

Legally, nothing can happen to a layperson who uses a publicly accessible defibrillator for first aid. According to Section 34 of the Criminal Code, this action falls within the area of ​​”justifying necessity” and takes place within the framework of the presumed consent of the person concerned.

How does a defibrillator work?

You can see them in companies, public buildings and subway stations: small defibrillator cases on the wall. They are identified by a green shield with a heart on which a green lightning flashes.

These automated external defibrillators (AED) are somewhat reminiscent of a first-aid kit with two cables, each end of which has an electrode pad the size of a postcard. These electrodes are placed on the chest when the heart is dangerously out of rhythm. The device then uses the electrodes to deliver small current surges in order to bring the heart back into its natural beating rhythm.

Fully and semi-automated defibrillators

There are fully automatic and semi-automatic defibrillators. The former deliver the power surge automatically. The semi-automatic devices, on the other hand, ask the first responder to trigger the impulse manually by pressing a button.

Using a defibrillator: how it works!

An AED (“layperson’s defibrillator”) is designed so that it can also be used safely and purposefully by laypersons: Pictures on the electrode pads show how and where the pads are to be attached. The device uses the voice function to announce the next moves and their sequence. Depending on the model, there is also an image-based guide via screen or drawings.

In concrete terms, you should proceed as follows during defibrillation:

  1. Free the patient’s upper body : A defibrillator can only be used on bare skin . The skin should be dry and hair-free. This is necessary so that the defibrillator can work efficiently and the patient is not burned by any sparks. Therefore, dry the skin on the upper body if necessary and shave if there is a lot of hair on the chest. A razor is usually included in the emergency kit for this purpose. Hurry to shave! Also remove band-aids and jewelry from the adhesive area.
  2. Attach the electrode pads : Follow the instructions – one electrode is placed on the left side a hand’s width under the left armpit, the other on the right side below the collarbone and over the nipple . If a second person was giving chest compressions, stop them now.
  3. Do not touch the patient during analysis : The defibrillator analyzes the patient’s heart rhythm and detects whether it is shockable or not (see below). Nobody should touch the patient during the analysis.
  4. Then follow the instructions that the device gives you : If it is a semi-automatic AED, in the event of ventricular fibrillation/fluttering, it will prompt you to press the so-called shock button. This triggers an electric shock. You can recognize the button by the lightning symbol. Caution: During the shock, neither you nor anyone else should touch the patient!
  5. Continue to follow the defibrillator’s instructions : for example, it may now ask you to resume chest compressions that were performed before the defibrillation.
  6. After about two minutes, the AED will call back to perform another analysis. Even then, follow the device’s instructions.

Perform CPR until emergency services arrive and treat or until the victim wakes up and is breathing normally. Let the electrodes stick on the chest.

Many AEDs contain the necessary accessories such as a razor, disposable gloves, clothes scissors and possibly a ventilation foil for mouth-to-mouth resuscitation and cleaning tissues, a small towel, a washcloth or handkerchiefs.

Defibrillator: Special features when used on children

Not all defibrillators are suitable for children under the age of eight or who weigh less than 25 kilograms – the shock would be too strong. Some devices have a device (e.g. sliders, child keys) to reduce the energy output.

Other defibrillators recognize themselves whether it is a child, for example when the enclosed, smaller pads are applied. They then automatically regulate the defibrillation energy downwards.

Cardiac arrest in children is very rare. In an emergency, it is better to use an adult defibrillator than to miss the chance to save the child’s life.

When do I use a defibrillator?

An automated external defibrillator (AED) is used when an unconscious person needs to be resuscitated . The defibrillator independently analyzes whether an electric shock makes sense at all. There are two types of heart rhythms:

  • Shockable rhythm : Here the heart muscle still has its own cardiac activity, i.e. it has its own electrical activity. However, this is at most out of step. These include ventricular fibrillation, ventricular flutter and pulseless ventricular tachycardia/pVT. They can be corrected by defibrillation. The device would therefore trigger an electric shock (fully automatic defibrillator) or prompt the first responder to press the corresponding button (semi-automatic defibrillator).
  • Non-shockable rhythm : There are two types of rhythm: Either the electrical (and mechanical) heart action has stopped (cardiac arrest), or there is electrical heart activity, but this is not converted into mechanical reactions (i.e. contractions) (pulseless electrical activity /PEA). In both cases, a defibrillator cannot do anything. He recognizes this during the analysis and will then ask the first responder to continue the chest compressions.

Defibrillation as part of resuscitation

The use of a defibrillator is one of the basic measures of resuscitation (basic life support, bls).

A mnemonic for the sequence of resuscitation is: check – call – push . Check consciousness and breathing , then call 911 and start chest compressions.

You can tell whether you need to initiate resuscitation measures for a person found unconscious by following the steps below:

  1. Test the person’s reaction: Speak out loud and gently shake their shoulders. If you are alone, it is best to call for help now, especially if the person is unresponsive.
  2. Check breathing by tilting the patient’s head back slightly and lifting their chin. Check for foreign objects in the mouth and throat that you can remove. Then the credo “Hear, see, feel!” applies: hold your ear close to the mouth and nose of the unconscious person – with your gaze towards the chest. Check for breath sounds, a puff of air, and the patient’s chest rise and fall. If the affected person is breathing independently, bring them into the stable lateral position.
  3. Call the emergency services or ask another person present to do so.

If you are unable to feel breathing (or breathing is severely abnormal) , then CPR should be started immediately and proceed as follows:

  1. Begin chest compressions immediately , preferably in combination with mouth-to-mouth resuscitation (if you or a bystander feel comfortable doing it). The frequency is the 30:2 rule, i.e. 30 heart massages and 2 breaths alternately. You start with chest compressions because there is usually still enough oxygen in the patient.
  2. If another first responder is present, have them fetch a defibrillator (if one is available) in the meantime. Use the device as described above.
  3. All of these measures are designed to ensure that blood continues to flow to the patient’s brain and heart until the emergency services arrive.

Start resuscitation (resuscitation) as soon as possible – even a few minutes without oxygen can result in irreparable brain damage or death of the patient!

Defibrillator for the home – useful or unnecessary?

According to the German Heart Foundation, there is no reliable evidence that a defibrillator makes sense at home or not. However, if an in-house defibrillator is available, it could be the case that someone delays making the emergency call or neglects manual resuscitation (cardiac massage and artificial respiration) or starts it too late.

The Heart Foundation therefore does not recommend purchasing a defibrillator for your own household. However, she advises anyone who still wants to buy one to seek advice from a heart specialist (cardiologist) beforehand.

Risks of using a defibrillator

If you stick the electrode pads directly over a pacemaker or another implanted device (often recognizable by a scar or similar in the chest area), this can impair the current impulses.

If you use the defibrillator on an unconscious person lying in water, there is a risk of electric shock! The same applies if you stand in a puddle while using the device. On the other hand, there is no problem using a defibrillator in the rain or at the edge of the pool.

You can also get an electric shock if you touch the patient while the device is delivering an electrical pulse. The danger is particularly high with fully automatic defibrillators that independently trigger energy pulses. Therefore, follow the instructions of the device exactly!

The electrodes must lie flat on the bare chest of the unconscious person. If the pads wrinkle , the current cannot flow. The function of the defibrillator is then limited.

Hurry to shave patients with excessive chest hair. If too much time passes before the defibrillator is used, it may be too late for the patient!

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