Building a DIY defibrillator in an emergency,

[Wallace Gasiewicz]

Just an oscilloscope does not work. We need to get rid of  the RF and especially 60Hz interference we have today.  You need a front end that will get rid of the common mode problems and amplify the ECG signal at the same time.There are DIY pretty simple units that do this. Even Google thinks so. But you need something else besides a scope.
Also the ECG lead connections are important to minimize any galvanic effects on the skin. , while making good connections. 
Silver plated leads were used when I first did an ECG along with special conductive paste, now the disposable leads contain the silver and the conductive paste (gel)
By the way EKG is the German of ECG.

https://www.nutsvolts.com/magazine/article/February2017_Build-ECG-EKG-Unit

[Psi]

yeah, using an oscilloscope to look at your heartbeat isn't as easy as it seems like it should be.
I've tried.

[AVGresponding]

By the time you've built your ad hoc defib it'll be too late to be of any use.

Far better to use a website like this https://www.defibfinder.uk/, or download an app to your smartphone.

[janoc]

By the time you've built your ad hoc defib it'll be too late to be of any use.

Far better to use a website like this https://www.defibfinder.uk/, or download an app to your smartphone.

An even better idea is to learn how to administer CPR and actually perform it, while having someone call the emergency services. Thinking about building anything or searching for a defibrillator on a phone when you have a victim on the floor in cardiac arrest is ... bonkers?

We are talking about minutes that person will survive without immediate help, tops. CPR might not save them either - but if you spend that time looking for gadgets and/or McGyvering something instead of working their chest, they will die for sure.

Something I was taught by an ER doctor - don't worry about breaking ribs or catching something because of mouth-to-mouth breathing. Both will heal but nobody can cure death. The goal is to keep the victim alive while help arrives. Also nobody can successfully sue you for breaking their ribs (or causing  other injury) while you were saving their life. OTOH, in many places you can be criminally prosecuted for not helping despite being able to.

[Psi]

Thinking about building anything or searching for a defibrillator on a phone when you have a victim on the floor in cardiac arrest is ... bonkers?

We are talking about minutes that person will survive without immediate help, tops. CPR might not save them either - but if you spend that time looking for gadgets and/or McGyvering something instead of working their chest, they will die for sure.

Something I was taught by an ER doctor - don't worry about breaking ribs or catching something because of mouth-to-mouth breathing. Both will heal but nobody can cure death. The goal is to keep the victim alive while help arrives. Also nobody can successfully sue you for breaking their ribs (or causing  other injury) while you were saving their life. OTOH, in many places you can be criminally prosecuted for not helping despite being able to.

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

[tautech]

yeah, using an oscilloscope to look at your heartbeat isn't as easy as it seems like it should be.
I've tried.

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:

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

[janoc]

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

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]

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.

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.

[Psi]

As a last resort, after CPR has been given for 30min, you might as well try and shock them.
At that point they are dead anyway and you have nothing left to lose.
Given that help is 12 hours away and both the people are now too exhausted from CPR to continue and continuing after 30 min is pointless anyway.)

No one is suggesting a DIY defibrillator is a good idea, except as a last resort before giving up.
The thread was only an engineering thought experiment.

[SiliconWizard]

If you are concerned about that case possibly happening and have had ample time to think about it, just buy an AED and put it in a safe, yet accessible place.

[Psi]

If you are concerned about that case possibly happening and have had ample time to think about it, just buy an AED and put it in a safe, yet accessible place.

'
Absolutely agree.

But this thread was an engineering thought experiment on building one when you don't have one.
You can all rest easy that I have no desire, or need, to build one 'just in case'. 
For any situation with knowledge ahead of time that one might be needed it would be moronic to build it when you can buy a proper one.

[SiliconWizard]

I think our words of caution were more aimed at random people possibly reading this thread rather than you in particular. In public forums, you never know who's gonna read what. (And now, what is going to end up in a AI model. )

Anyway, technically speaking - and not meant as advertising for AD, but purely to give some ideas about how an AED is designed, you can have a look at this:
https://www.analog.com/media/cn/technical-documentation/apm-pdf/adi-aed-solutions_en.pdf

And otherwise this:
https://www.sciencedirect.com/science/article/pii/S2468067217300354

[NiHaoMike]

What about the case where one is trying to save a pet rather than a person? That might make things easier as the smaller size means a lower voltage.

[AVGresponding]

By the time you've built your ad hoc defib it'll be too late to be of any use.

Far better to use a website like this https://www.defibfinder.uk/, or download an app to your smartphone.

An even better idea is to learn how to administer CPR and actually perform it, while having someone call the emergency services. Thinking about building anything or searching for a defibrillator on a phone when you have a victim on the floor in cardiac arrest is ... bonkers?

We are talking about minutes that person will survive without immediate help, tops. CPR might not save them either - but if you spend that time looking for gadgets and/or McGyvering something instead of working their chest, they will die for sure.

Something I was taught by an ER doctor - don't worry about breaking ribs or catching something because of mouth-to-mouth breathing. Both will heal but nobody can cure death. The goal is to keep the victim alive while help arrives. Also nobody can successfully sue you for breaking their ribs (or causing  other injury) while you were saving their life. OTOH, in many places you can be criminally prosecuted for not helping despite being able to.

Oh FFS do I have to explicitly state the implied context? Of course this is in ADDITION to performing first aid, which would include CPR, when and where appropriate, after ensuring there is no danger extant to yourself or the patient.

Where I work, first aid courses are mandatory, with regular refresher courses.

FWIW you can't be prosecuted for either trying to help or not trying to help, in the UK.

[SiliconWizard]

FWIW you can't be prosecuted for either trying to help or not trying to help, in the UK

Really? In some cases, "not trying to help" is akin to failing your "duty to rescue", which I guess varies from country to country in terms of the law, but isn't there something like this in the UK? That would be interesting.

Of course, the duty to rescue doesn't mean trying to do medical acts that you don't master at all on someone, if that's what you meant by "help". I guess the minimum you'd be expected to do when witnessing that someone has suffered a cardiac arrest would be to call the emergency services. If you can't, that would be trying to find help another way, as much as you can. No one's gonna expect from you than you'll save someone with a magical act that you have no clue about, unless it's actually your job.

Conversely, doing something provably dumb or excessively risky considering the circumstances, especially if you are aware of the risks (say you are an engineer, you're supposed to know what kind of risks you'd take here by making a DIY defibrillator or something like that), I have a hard time believing it won't get you to being prosecuted and facing court.

Would be interested in hearing more about the UK's law, and if indeed you'd never be prosecuted from trying something really stupid and dangerous to help someone. That would look like a can of worms if that were really the case.

[AVGresponding]

I probably should have said "won't" instead of "can't", but in practice, it just doesn't happen.

My guess is if you made a DIY defibrillator and the patient died after you used it, there's a definite possibility of prosecution, depending quite a bit on the findings of the Coroner.

[SiliconWizard]

I probably should have said "won't" instead of "can't", but in practice, it just doesn't happen.

My guess is if you made a DIY defibrillator and the patient died after you used it, there's a definite possibility of prosecution, depending quite a bit on the findings of the Coroner.

Yeah, now from a legal POV, that's still an interesting point I think - from what I have read in the meantime (nothing deep so far though), there indeed doesn't seem to be anything like a formal "duty to rescue" in UK's law, while there is in some other countries. But someone more knowledgeable in UK's law system can possibly correct this or add some precisions.

[Wallace Gasiewicz]

In response to Halcion:
You are essentially correct, in my opinion.
In addition the quality of the "shock" delivered has changed with technology improvements and medical observations of the type of shock effect experimentally in laboratory animals.
There is no way to quickly develop a modern "shock" that is delivered by current defibrillators.I suppose the first defibrillator that I used would be considered quite unsatisfactory in today's world. This was more than 50 yrs ago.

In addition there are differing opinions as to when to terminate unsuccessful CPR. This is an ongoing argument. More than 30 min?
The other thing to consider is how quickly is a defibrillator likely to arrive on the scene. The sooner the better.
The silliest thing I have repeatedly seen in Movies and TV shows in the past is the application of a common AC wall outlet jolt to a victim. This is likely to produce more trouble than it can possibly alleviate.

[SiliconWizard]

The silliest thing I have repeatedly seen in Movies and TV shows in the past is the application of a common AC wall outlet jolt to a victim. This is likely to produce more trouble than it can possibly alleviate.

Mr. Bean illustrates it brilliantly by making a parody of this.

[johansen]

Is it 2000v or 300v needed to dump enough current?


4kv from a fully charged microwave oven cap is 4 to 8 joules assuming you can ensure you dont make a 500ma constant current source that does more than you want it to. The internal 10M ohm bleeder resistor means you have half a second to apply the pads or you lose half the charge.

340 from a dumb pwrsup or 400 volts from a pfc corrected supply is probably a bad idea

[antenna]

CPR will not correct fibrilation (afaik), but the Modified Valsalva Maneuver might.  By sitting up with legs extended and blowing into something to increase chest pressure, blood is forced out of the heart.  After 10 seconds of this, you lay the patient on their back quickly while riasing their legs in the air.  That causes the blood to rush back in and the pressure stimulates a nerve (in the aorta i believe) and resets the heart rhythm.  It has a high sucess rate for SVT but, but from my understanding, only about 50% sucess for vfib. I have SVT, which for those that dont know is terrifying,  and that trick fixed it twice.  Scary sensation though, both SVT and when the Valsalva maneuver corrects it.

[AVGresponding]

My point about finding an actual defib machine rather than trying to ghetto-fab one, is that a proper one will give you verbal instructions on how to use it, and knows whether and when to deliver a shock. You just can't know if a patient is in VF or the heart is stopped unless you're a medical professional with the correct tools. It's pretty easy to miss a weak pulse, even if you're a medical professional without tools, and giving a shock to someone in that situation is going to kill them.

There are lots of these things in public places nowadays, in the UK anyway, and the number keeps going up.

https://www.nddb.uk/

In short, go do a PROPER first aid course, and get a defib locator app on your phone. If you work in or near a public building in the UK, there will be one nearby; take the time to learn where it is.