A Brief Explanation of How a Defibrillator Works

February 24th, 2023

24/2/2023

A Brief Explanation of How a Defibrillator Works

24/2/2023

In the 21st century, electrical defibrillation has proven to be the most effective treatment for cardiac arrest caused by ventricular fibrillation (VF) or pulseless ventricular tachycardia. There is sufficient scientific evidence that favours early defibrillation, which states that the time between collapse and the administration of the first shock is the most critical factor of survival. Survival rates of up to 75% have been observed when defibrillation is administered immediately. On the contrary, the chances of a favourable outcome result decrease by around 10% for every minute cardiac defibrillation is delayed.
The invention of an automated external defibrillator has been of great help to victims in NZ, who might have suffered cardiac arrest at their homes or in public places that are far away from healthcare institutions.
This blog post will allow you to understand the principle of an automated external defibrillator, its various types available in the NZ market today, its applications and its limitations.
Different types of defibrillatorsMost defibrillators are based on energy—the device charges the capacitor to a certain electrical voltage and then delivers a certain amount of energy in joules. The amount of energy that reaches the myocardium depends on the voltage chosen and the transthoracic impedance (which refers to the dissipation of energy in the lungs, thoracic cage, and other parts of the chest), which varies from one patient to another.
Most of the contemporary Automated External Defibrillators (AEDs) in NZ are powered by electricity, but there are two other types of defibrillators that aren't used as often in the real world.
Impedance-based defibrillators let you choose how much current to use based on the transthoracic impedance (TTI), which is first checked with a test pulse, and then the capacitor charges to the correct voltage. Compared to the energy-adjusting defibrillators, this method had a big impact on the success rate of shocks in people with a high TTI.
Current-based defibrillators use a fixed amount of current to set defibrillation thresholds that are independent of TTI. The best amount of current for ventricular defibrillation appears to be 30 to 40 amperes, regardless of both TTI and body weight, which means less energy is used than with the old method. This is because the new method doesn't use the same amount of energy.
Automated External DefibrillatorsDefinitionThis is a term that refers to a computerised device, that’s easily portable and is lightweight. It comes with rhythm analysis and defibrillation systems, and it tells people how to defibrillate anyone who has gone into cardiac arrest because of VF or pulseless VT.
There are two types of AEDs: semi-automatic and fully automatic. The semi-automatic AED tells the operator that the person needs to be defibrillated, but the operator has to push a button to deliver the shock. In the case of the fully automatic one, the device can administer the shock, without any external help.
Basic AED componentsThe devices comprise of the following components:

Batteries
Capacitor
Electrodes
Electrical circuit
Controls

Defibrillation successDefibrillation is said to be successful when it stops ventricular fibrillation (VF) for at least five seconds after the shock. DFT (Defibrillation Threshold) is the lowest amount of energy that can be used to get the heart rate back to normal. Defibrillation depends on the accurate selection of energy and TTI.
How to use an Automated External Defibrillator in NZSTEP 1:
Power it up. This lets the operator get a text or a voice prompt that will help them with the next steps.
STEP 2:
The electrode pads should be plugged in now. Place the self-adhesive electrodes on the victim’s skin, as it may be illustrated on a pad or AED. An alert message will appear if there aren't good connections between electrode pads and the skin, so the rescuer should check them first.
STEP 3:
Analyze the rhythm. The rescuer must ensure that the victims aren’t manhandled by anyone else and they themselves should also refrain from making any movement. In some devices, the user might need to press the “ANALYZE” button, whereas, in the case of others, it happens automatically, as soon as the electrodes are attached. If the VF is there, it will announce a message, visual or an alarm.
STEP 4:
Press the SHOCK button. There will always be a clear message that says "clear the patient." Most of the time, when a treatable rhythm is found, the capacitors are automatically charged.
Integrating AED use with Basic Life Support systemWhen rescuers arrive at the incident site, they must immediately begin cardiopulmonary resuscitation (CPR) and use the available AED. In general, three things must happen at the same time:
(1) activating the Emergency System
(2) CPR and
(3) Usage of the AED

Chest compression should start as soon as possible. It must be continued while the adhesive pads of the AED are being attached and the defibrillator is charging. The rescuer should first put on the pads and then start chest compressions. If there is only one rescuer present, they should start with chest compressions only without the ventilation. But when there are two or more rescuers present at the site, chest compression and ventilation should be done in the 30:2 order.
The CPR interruptions should be kept to a minimum range. All guidelines stress how important it is to start chest compressions early and keep them going for a long time. Only stop CPR when it's important to look at the rhythm and give a shock. Defibrillation should be possible with a break in chest compressions of no more than 5 seconds. After a person gets an electric shock, it is important to start CPR right away for the next two minutes. Only then should you stop to reanalyze the heartbeat again.
Under the old guidelines, CPR was supposed to be done for 2-3 minutes before analyzing the rhythm. Now, this suggestion has been scrapped because of its ineffectiveness.
For any VF taking place outside the hospital premise, the three-shock recommendation is also no longer valid either. To use this strategy, you should only use it if you have seen VF happen in a hospital setting, like in the cath-lab or for people who have had heart surgery in the past. When someone has a cardiac arrest outside of the hospital, they should get an initial shock if they're in VF, then two minutes of CPR, and then have their heart rhythm reanalyzed.
Electrode pastes and gels can spread between the two paddles, which could cause a spark. Hence they should not be used.

Modified prototype AEDs keep track of how often and how deep chest compressions are during CPR. These devices are now on the market and can help rescuers improve their CPR skills.
ConclusionSudden cardiac arrest, which often happens because of VF or pulseless VT, is traditionally not recommended to increase your chance of survival. With manual defibrillators, only qualified rescuers who can read ECGs can help these patients. This is because manual defibrillators can only be used by people who know how to use them. AEDs solve this problem because they can look at the rhythm and tell rescuers if they need to shock the person.
When someone has a cardiac arrest outside of the hospital, rescuers can use this method to provide effective early defibrillation, which has been shown to significantly increase survival and survival with intact neurologic function. One problem with using an AED is that it interrupts CPR, which can be bad for people who can't be shocked. To improve rhythm analysis and "hands-off" time during CPR, a lot of research and innovation is still in progress.
To know more about Automated External Defibrillator in NZ, get in touch with our team today.

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February 24th, 2023