Transcutaneous Monitoring of Oxygen Saturation
Also known as pulse oximetry. This is done by a small device clipped over the finger or other extremity that uses absorption red and infrared light to measure the level of oxygenated haemoglobin in pulsatile (i.e. arterial) flow. Veins do not pulsate and so are ignored by the monitor. CarboxyHb from CO poisoning also absorbs light in the same way as OxyHb and so will have normal SpO2.
- Remember when talking about "O2 sats" (like in your favourite medical drama!) to be clear about what you mean. SpO2 (pulse oximetry), PaO2 (arterial blood gas) and oxygen content (Hb, PaO2) all measure oxygen but only the first is properly called "O2 saturation". A normal PaO2 might imply that someone's "sats" SHOULD be high, but remember your haemoglobin binding curves (like in Boron... not so exciting); if temperature or pH are abnormal, and they may be in sick people, you can get pretty poor saturation levels at normal PaO2.