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...
COVID causes blood O2 to drop because it causes a viral pneumonia. Early stages of a viral pneumonia can be pre-symptomatic or entirely asymptomatic. Asymptomatic patients can still transmit COVID to others. Patients with low oxygen should seek medical attention because their pneumonia can get worse.
Your source says “Many patients with COVID-19 disease have low oxygen levels even when they are feeling well.” These patients have low oxygen because of COVID pneumonia.
Your (uncited) claim that "These patients have low oxygen because of COVID pneumonia." There are plenty of sources out there[1] that talk about a strange, again, leading indicator, known as "silent hypoxia" which has nothing to do with pneumonia. Further, there's a lot of confusion in your post: if COVID ends up giving you pneumonia, you are definitionally not asymptomatic.
You are mistaken. You can have pretty much any diagnosis and there is no “definitional” reason you must be symptomatic.
Pneumonia is a diagnosis (well, class of), not a symptom nor a sign, which are distinct terms of art. You can have pneumonia that shows up on a chest X-ray (a sign) without any symptoms.
A better example might be high blood pressure, which many people understand can be silent/asymptomatic for years but is easily measurable.
Point still stands, symptoms are noticeable and reportable by the patient. If covid gives you pneumonia you may still be asymptomatic.
> You can have pneumonia that shows up on a chest X-ray (a sign) without any symptoms.
Your post is a bit confusing, I'm not exactly sure what you're arguing. Walking pneumonia (which is what you're describing; the term of art is atypical pneumonia) is extremely rare, and it's not what we're talking about here. Non-atypical pneumonia has symptoms, ergo is by definition not asymptomatic.
What problem if you don't mind? I have a Garmin that says I'm 94ish, though it's accuracy is questionable. Haven't had a chance to test with a proper one.
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 you fall even lower. Doctors then usually instruct nurses to adjust the flow so saturation stays in the 90-95 range.
People at high altitude or in airplane cabins can be at 70% for hours without even noticing. Meanwhile someone having a dip from 90 to 80 with pneumonia might be gasping for air.
Pulse oximeters are not all that simple. The general idea is easy enough to get across and it's possible to build a fairly simple one that will work some of the time. But the top end, highly reliable ones that work well at low sats are pretty complicated things.
Interesting. You're probably not the right person to ask about this sort of thing and I should probably stick with a doctor's opinion, but you may have a better intuition than I do about the reliability of these things' readings.
Suppose I use a pulse oximeter and I get readings of 90%, 91%, 92%, and 99%, all taken ~one minute apart.
Is it most likely that I am fine and there were some issues either with the hardware or its administration? Or is it possible to get spurious high readings?
For what it's worth I had this same experience at the doctor's today for my physical.
Former research engineer (intern) at a pulse oximiter company.
This was about 18 years ago, so the details are shaky.
Yes, this is likely the probe calibrating itself. Recall that the SpO2 is based on the ratio of two measurements. From TFA, you can see that the absorption in the IR is pretty flat, so the IR LEDs don't need to be known with much accuracy - and the IR LEDs you buy are also generally in narrow tolerances because of the telecom industry using them for fiber too. But on the Red side you have a steep slope for one of the spectra, that means that you need to have a better understanding of the wavelength of red LED you're using.
But you know where you get red LEDs? Cheaply? From traffic light manufacturers. In bulk. Apparently it's much cheaper to buy LEDs in huge quantities and pay in intern to develop a measurement device to test every single LED to determine the wavelength. (And probably sell the rest back into the traffic light supply chain.)
Even after that, the red LEDs wavelength was very dependent on temperature (your finger warms it up, for example) and even the current coming in from the probe.
I never worked on the FDA approved code, but there was a bunch of pre-processing put into the sensor to determine the red LED wavelength and make calibration changes before the signal got downstream to the main instrument.
I'm sure any pulse oximiter you buy off of Amazon doesn't go through the calibration that the FDA approved ones do.
Fun fact. As an intern when you're poor, it sounds like a good idea to do calibration studies: they put pulse oximiters on every finger and your earlobes and then have a nurse administer air to you and slowly bring your SpO2 down to 70% while watching the response of the sensors. Talk about light headed! And then they take the mask off and you pop back up to about 95% (our office was a 5000 feet, not sea level) in a minute or two. Fun and you get a $50 gift certificate.
It often takes a while for the probes to stablise and get an accurate reading, so this is a very common pattern, but I haven't looked into why. I think part of it may be the machine calibrating to the flow of blood through the area of skin you have chosen. You often apply the probe and sit it there for 30-60s waiting for it to stabilise.
If you are worried, ask them to leave it on throughout your consult. You should see it sit at 99-100% for the rest of your stay.
> I should probably stick with a doctor's opinion, but you may have a better intuition.
Yes, you should trust your doctor over strangers over the internet. They should have much more context as well. It's one thing to comment on equipment, but it is another to comment on what that result means for you.
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.).
