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Building a DIY defibrillator in an emergency,
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tautech:

--- Quote from: Psi on September 27, 2023, 08:33:26 am ---yeah, using an oscilloscope to look at your heartbeat isn't as easy as it seems like it should be.
I've tried.

--- End quote ---
How hard ?

It need be a differential measurement and skin conductivity needs be improved.
Got any conductive zinc based heatsink compound ?

I do have a stash of used ECG pads saved from a few days in a Cardiac ward especially to have a play around scoping with but as yet not had the chance and these do have a connection nipple that a probe hook could attach to.
Wallace Gasiewicz:
You really do not need timing in V Fib,you just shock   
You assume there is no discernible rhythm because that is the most likely scenario.In cardiac arrest the rhythm, if there is any, will degenerate to v fib. 

This is absolutely true:
--- Quote ---Even if both of you are fully trained in CPR, you still need the defibrillator within the 20-30 min
--- End quote ---
janoc:

--- Quote from: Psi on September 27, 2023, 08:46:09 pm ---
You're forgetting the original scenario in this thread. 
There's another person able to give CPR, there's no hope of getting any help within 12 hours due to your location.
So you might as well try and build something to shock the person. You don't have much time, maybe 20-30min, but that might be long enough to smash apart some devices and add extra caps onto one of them to make 325V DC with some energy behind it. (probably only going to work in 230VAC countries, 110VAC would need voltage doublers and that is getting to complicated)

Even if both of you are fully trained in CPR, you still need the defibrillator within the 20-30 min

--- End quote ---

Even in that scenario you are more likely to kill the person with your gadget than to help. Moreover, you would do better helping or swapping with the person administering the CPR so that they can rest because it is very exhausting, esp. if you are doing both cardiac massage and breathing at once and alone.

Also, don't forget that if victim doesn't get help for whatever caused them to keel over in the first place, you can CPR/shock them as much as you want, they will die - and much faster than in those 12 hours. If they are having a heart attack this serious, they are certainly not going to survive without immediate medical attention, regardless of whether you shock them or just keep doing CPR for hours. That vein blockage won't clear itself even if you stop the fibrillation.

And that assumes you are 100% sure they have a heart attack - a person can suddenly keel over and have no pulse for various reasons, which you can't determine as a layman by merely looking at them.

The defibrillator helps only in one specific situation, which is the reason why the units intended to be used by laymen always have a built-in diagnostics that will not let you shock the patient when the conditions are not met - you could kill them! It is not a magic "save life" button.

You are solving a non-existent/completely wrong problem.
SiliconWizard:
Agreed, that would also assume that you have the required parts lying around where you are, but no access to an emergency service. Yeah. Maybe if you live in Antarctica or something and have lab equipment because you are on scientific program. In which case, you'll probably have commercial defibrillators with you anyway. It's probably more a rhetorical question than anything else.

Also note that if the person dies after you have administered your DIY shocks, you will probably be under investigation and may end up in jail. (Unless again it can be proven that you had absolutely no access to any kind of medical help whatsoever.) Just saying. Don't do it.

Halcyon:

--- Quote from: Psi on April 24, 2020, 02:23:19 pm ---Breathing air into the lungs is no longer considered necessary for CPR. I'm not sure of the details but apparently the lung muscles do move a little while in ventricular fibrillation and you get enough oxygen to keep the brain alive with just chest compression.
However, i'm not sure how well that works for hours on end. so yeah, might need extra person.

--- End quote ---

Emergency services are trained in rescue breaths however they are entirely optional. There are cases where the first responder is unable or unwilling to give rescue breaths and that is perfectly fine (and won't expose you to any litigation if you simply refuse). After 30 chest compressions, 2 rescue breaths is still the recommendation. Rinse and repeat. If rescue breaths are not given, by compressing the chest cavity, you are still causing some air to enter and be expelled from the lungs anyway. If you don't know what you're doing, just stick with compressions (they should be deep enough where you might break ribs).

In relation to the OPs question, my (basic) understanding is that AEDs (Automated external defibrillators) are only effective if the heart muscle in a particular state of tachycardia or fibrillation. After a series of compressions, the AED will instruct the first aider not to touch the patient while it measures what the heart is doing. If it detects that neither condition exists (or if the heart has stopped entirely), a shock will not be delivered.

Manual defibrillators (such as those you see in Ambulances and hospitals) will allow shocks to be delivered in a wider range of circumstances, but are more complicated to operate and require proper training to be effective.

As for the shock that is delivered from the AED itself, they will deliver a shock with a biphasic waveform, I guess similar to AC. The first phase of the shock is generally <=10 milliseconds in duration.

In any case, if chest compressions can be started early and maintained until emergency services arrive, I would say the patient has a far better chance of survival as opposed to attempting any kind of home-brew defibrillation which might put the heart in a state where an AED could be rendered ineffective. If you render first aid as per your training, you won't/can't be sued for negligence even if the patient dies. If you start messing around with mains power and the patient dies, that could be on you. The other consideration is that in a panic and in the heat of the moment, you might be exposing others or yourself to unnecessary danger.
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