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How Pulse Oximeters Work (2015)

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Re: How Pulse Oximeters Work (2015)

#61

Post by asveikau »

alkonaut wrote: post #32
asveikau wrote: post #29

Earlier quoted context omitted.

I thought I recall reading that 94 is not dangerous or abnormal, and 90 is when you should get checked out.

This is something that is still not quite understood by doctors. I take my kid (Who has a respiratory condition) to hospital at 90. In my experience if you are in hospital with oxygen because of a respiratory illness, the oxygen would probably be given once you dip below 92-93 assuming they know you have a respiratory condition. Not because that’s the danger level but because they want to be able to tweak the O2 if y…

Sorry to hear about your kid. Must be hard on both child and parent. I wish everybody well.

Re: How Pulse Oximeters Work (2015)

#62

Post by joshgel »

bdcravens wrote: post #57

The most painful thing I've experienced medically was an arterial blood draw to measure my o2 sat levels. (They numb your inner wrist with novocaine then go in with a giant needle to the artery deep in there. If it's that painful numb, I can't imagine what it'd be like otherwise. And each time it was no more accurate than the pulse oximeter.

Most of the time we don’t numb patients to be honest. I’ve had it done to me, we practiced on each other in Med school. It is painful, but I suspect the Novocain you got didn’t work because it’s the artery that’s painful not the skin.

But it does give you different information than a pulse ox. For example, people can have respiratory failure from too low oxygen (captured on a pulse ox), but also from top high CO2 (not measured on pulse ox). It also gives a measure of acid-base status, which can be thrown off for a variety of reasons (usually renal or respiratory). It is used somewhat too much in my opinion but can be life saving in some situations.

Re: How Pulse Oximeters Work (2015)

#63

Post by mturmon »

DangerousPie wrote: post #31
mturmon wrote: post #22

Earlier quoted context omitted.

I purchased a relatively cheap one from Amazon a couple of months ago. Less than $50, I believe. I tried some simple stuff when it arrived. I believe I was able to get it to swing within the 94-99% range by holding my breath and by deliberate, deep breathing, over the span of just a minute or two. It definitely was not pegged at 99%. The changes were surprisingly fast. My wife was able to get the same response. If it…

How long did you hold your breath for?

Perhaps 30 seconds? It was uncomfortable but not a big strain. I see someone nearby saying 2-3 minutes. For me, it was not that long!

Re: How Pulse Oximeters Work (2015)

#64

Post by joshgel »

dvt wrote: post #3

Went to a party last weekend where the host used a pulse oximeter (and thermometer) on everyone. Blood O2 level is apparently a leading indicator of COVID-19. Pretty cool stuff. The inner workings of it are actually quite simple as well, pretty amazing that it works as well as it does.

It’s probably a leading indicator of COVID pneumonia but that probably still takes some days to develop during which time infected people are still contagious. Probably better to stay home or at least wear a mask...

Re: How Pulse Oximeters Work (2015)

#65

Post by OJFord »

DangerousPie wrote: post #17

Does anybody have any suggestions for how to check whether a pulse oximeter actually works properly? I bought one online from a not particularly trustworthy shop. I have never seen it show any value other than 99%. How can I figure out whether it actually does anything and doesn't just show 99% no matter what?

To test it's accuracy or just to see if it ever shifts from 99% (or random fluctuations)? For the latter you you'd just use inorganic material of varying thickness/opaqueness.

Re: How Pulse Oximeters Work (2015)

#66

Post by renewiltord »

DangerousPie wrote: post #17

Does anybody have any suggestions for how to check whether a pulse oximeter actually works properly? I bought one online from a not particularly trustworthy shop. I have never seen it show any value other than 99%. How can I figure out whether it actually does anything and doesn't just show 99% no matter what?

Held my breath till I nearly passed out. Watched the indicator tick down. You'll start seeing stars and the meter should be matching you.

It is hard to do so normally so I forced the air out and then pinched my nose shut with my fingers to prevent accidentally breathing in.

Re: How Pulse Oximeters Work (2015)

#68

Post by wtallis »

dmitrygr wrote: post #48
alister wrote: post #39

Earlier quoted context omitted.

The author explains his visualization as follows: One is a red light, which has a wavelength of approximately 650 nm. The other is an infrared light, which has a wavelength of 950 nm. (Throughout our description, we will show the infrared light in light blue. In reality, infrared light is invisible to the human eye.)

i mean this, for example: https://web.archive.org/web/20191230203925im_/https://www.ho...

The fact that those curves don't even come close to resembling sine waves seems more wrong to me, and really helps drive home the fact that the diagram was made in MS Paint with little regard for accuracy.

Re: How Pulse Oximeters Work (2015)

#69

Post by dialamac »

bdcravens wrote: post #57

The most painful thing I've experienced medically was an arterial blood draw to measure my o2 sat levels. (They numb your inner wrist with novocaine then go in with a giant needle to the artery deep in there. If it's that painful numb, I can't imagine what it'd be like otherwise. And each time it was no more accurate than the pulse oximeter.

An Pulse Ox and ABG are not interchangeable exams, with the ABG giving a lot more data about respiratory and metabolic derangements. A pulse ox can also be outright fooled such as in cases of carbon monoxide poisoning or essentially wrong in other poisoning. Also for a wrist ABG there’s no reason to use a giant needle. A 23g is usually fine, length is usually not an issue as the artery is actually quite superficial. For reference, an 18 gauge is the smallest that might be considered “large”. And the sizes are bigger as the number gets smaller.

Re: How Pulse Oximeters Work (2015)

#70

Post by dvt »

leetrout wrote: post #59
dvt wrote: post #3

Went to a party last weekend where the host used a pulse oximeter (and thermometer) on everyone. Blood O2 level is apparently a leading indicator of COVID-19. Pretty cool stuff. The inner workings of it are actually quite simple as well, pretty amazing that it works as well as it does.

You may not choose to reply if you see this but I'm going to ask anyway: I'm curious if you were concerned about going to the party?

Not really. It was a very small gathering (< 10 people) mostly with people I already had spent a lot of quarantine with (doing camping, kayaking, etc.).
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