The O2 saturation test involves just clipping a plastic thing–like a clothespin–onto the finger. It is not tight, it does not pierce the skin, but somehow it still works. How?
By shining light through the clipped flesh and measuring the difference in transmission between oxygenated and non-oxygenated blood.
Well, it doesn’t actually tell you the percentage of oxygenated blood. What it tells you is the percentage of bound hemoglobin. It can tell this because the bound hemoglobin folds into a different shape.
While typically this doesn’t make a difference, it can in some cases. For example, hemoglobin has a much higher affinity for carbon monoxide than it does for oxygen so in cases of CO poisoning someone could be showing a sat of 100% but still be hypoxic.
Also, it can’t tell you how much hemoglobin the person has, so someone could still be hypoxic with a sat of 100% because their crit is too low.
St. Urho
Paramedic