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Regarding the oxygen saturation levels that have been so much in focus the last few days (the usual thresholds for starting intubation might be wrong for Covid-
by usrusr 7y ago
Regarding the oxygen saturation levels that have been so much in focus the last few days (the usual thresholds for starting intubation might be wrong for Covid-19 patients): is this a metric that is measured directly or is it usually derived from proxies? That's what my debugging instincts are shouting whenever I read something about the oxygen saturation mismatch, it would be easy to get misled of the proxies have never been (noticeably) unreliable before.
- maxerickson 7y agoIt's relatively direct: https://www.lung.org/lung-health-diseases/lung-procedures-and-tests/pulse-oximetry https://www.lung.org/lung-health-diseases/lung-procedures-an...
- nradov 7y agoPulse oximeters measure the light absorbed by hemoglobin. So that's pretty much a direct measurement, I don't think it could be wrong. https://opentextbc.ca/vitalsign/chapter/why-is-pulse-oximetry-used/ https://opentextbc.ca/vitalsign/chapter/why-is-pulse-oximetr...
- Trasmatta 7y agoWhen this first started popping off, I ordered one of them on Amazon. If I get it, it should help give me info on if / when I would need to go to the hospital.
- dharma1 7y agoSame here. You can get a fitness band that measures SpO2 among other things for 30 bucks or so
- darkerside 7y agoMost recent Samsung Galaxies have one built in. You just need to enable it in the Samsung Health app.
- nradov 7y agoI have a Samsung Galaxy myself but it's less accurate than a real medical device. Readings depend on how you hold your finger against the sensor.
- darkerside 7y agoI think you'd only be looking for a significantly low reading anyway. So if you get a low reading try again until it goes up or it's time to go to the hospital.
- usrusr 7y agoCouldn't there be a million other things that change light absorption?
- ajross 7y agoNot inside a body, no. These aren't the most accurate tests (the big failure mode has nothing to do with the science, it's that the little clamp falls off the finger), but they are very mature technology with well characterized behavior. Basically everyone who's been under anaesthesia of any kind (even stuff like wisdom teeth removal) for the past 3-4 decades has had one of these on them. We know how they work.
- wenc 7y agoI read that despite the simple measurement mechanism ("shine a light through a finger"), the accuracy is generally pretty high (+/- 2%). This document from the American Thoracic Society does state some corner cases though [1]. Quote: "How accurate is the pulse oximeter? The oxygen level from a pulse oximeter is reasonably accurate. Most oximeters give a reading 2% over or 2% under what your saturation would be if obtained by an arterial blood gas. For example, if your oxygen saturation reads 92% on the pulse oximeter, it may be actually anywhere from 90 to 94%. The oximeter reading may be less accurate if a person is wearing nail polish, artificial nails, has cold hands, or has poor circulation." [1] https://www.thoracic.org/patients/patient-resources/resources/pulse-oximetry.pdf https://www.thoracic.org/patients/patient-resources/resource...
- wallflower 7y agoOne very important thing to note is that the Oxygen - Hemoglobin dissociation curve has a sigmoidal shape. It is not linear. After a certain point, around 90 %, there is a very sharp drop-off. https://en.m.wikipedia.org/wiki/Oxygen–hemoglobin_dissociation_curve https://en.m.wikipedia.org/wiki/Oxygen–hemoglobin_dissociati...
- yread 7y agoI read speculation based on protein protein docking, that it could limit ability of hemoglobin to bind oxygen. On the other hand it can't enter red blood cells so it does not make sense. But I think you would see high blood oxygenation even in a person with CO poisoning as it just measures whether something is bound to hemoglobin