How are blood Oxygen levels determined via a Pulse Oximeter?
Basically, the oximeter consists of a light source with two lights of different wavelengths, and a sensor. It is clipped to the patient (usually a finger, but you can use a toe or an earlobe) so the lights shine through the tissue and is measured at the other end – oxygenated hemoglobin and deoxygenated hemoglobin absorb light at different wavelengths, so by measuring the relative amount of light that is transmitted through by the two light sources, you can calculate the percentage of hemoglobin that is oxygenated. It’s not perfect though – notably, when carbon monoxide is bound, to the pulse ox, it will look exactly the same as if oxygen were bound, so someone with CO poisoning will show a 100% “oxygen saturation,” but will probably actually be in very bad shape.
