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This is a discussion on How does an O2 sat monitor work? in General Nursing Student, part of Nursing Student ... After taking pts' O2 sats for so many semesters, I realize that no one's ever explained to me...by NTPinky Sep 29, '05After taking pts' O2 sats for so many semesters, I realize that no one's ever explained to me exactly how they work! I'd like to know since I'm sure one of my pts will someday ask me! I know the laser is involved, but how just how does it work to reveal the O2 level in the blood??
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- Sep 29, '05 by freshdHiya, first post - sorry if i'm a little vague, as I'm don't fully comprehend how these things work myself (not a physicist).
So, from what I gather, the LED (light emitting diode) in the finger thingy (the technical term) sends out 2 wavelengths of red light (which you saw already). The light travels through the finger, appendage, or whatever and reflects against the RBCs and the hemoglobin they contain (carrying oxygen or not), and out to the other side where the sensor on the other side of the probe sends the data to the computer. Using (apparently) well-established algorithms, we're able to extrapolate the percentage of oxygenated blood at the measurement site.
Incidentally, here's an interesting article about the benefits and shortfalls of using pulse oximetry:
If you have one molecule of hemoglobin that's fully oxygenated travelling around in your body, your SpO2 is 100% - but obviously not perfusing adequately!
I've heard anecdotally that this technolgy was invented by someone at Stanford in the 90's - there are some interesting research articles on it's use on animals over on PubMed.
All the best and keep asking questions!
daveLast edit by freshd on Sep 29, '05 : Reason: typo
- Sep 29, '05 by DaytoniteThe pulse oximeter is actually a computerized gizmo that gives you a ratio of the saturated hemoglobin compared to the unsaturated hemoglobin that it detects expressed as a percentage. It actually emits two different lights, a plain old red light and an infrared light which noninvasively pass through tissue. A sensor which is opposite the two light sources is able to compute the amount of light that is passing through tissue. One of the lights is absorbed by hemoglobin molecules and the other is not. The results of what the light sensor detects from the two different lights is what forms the ratio of saturated to unsaturated hemoglobin that is then mathematically expressed as a percentage.
The aparatus must be able to detect a pulse that is strong enough to bring enough blood flow into the area so the little light is going to be able to bounce off an adequate number of hemoglobin molecules so the ratio can be computed. The pulse must be rhythmic. Pulse ox doesn't work very well in people who have very irregular heart beats.
- Sep 29, '05 by Curious1alwysWow, good question. Very good answers too! You guys are SO smart!!
- Sep 29, '05 by rjflynas a side note they can also give one a false sense of security in a patients condition. the bigest example is a pt with carbon monoxide poisoning. the will and can read 100% saturation. the pulse ox cant tell the difference between o2 and co. although is did just see the other day that they now have a pulse oximeter that can.
- Aug 17, '12 by zhillzThe best answer I've found on the internet is a pdf at this address:
Quote from NTPinkyAfter taking pts' O2 sats for so many semesters, I realize that no one's ever explained to me exactly how they work! I'd like to know since I'm sure one of my pts will someday ask me! I know the laser is involved, but how just how does it work to reveal the O2 level in the blood??
Thanks!Last edit by Esme12 on Aug 18, '12
- Aug 18, '12 by Esme12Although this thread is 8 years old.......it is good to re-visit some information as it always valuable. Thanks!