How do the hospital medical machines measure your oxygen saturation just by having the little clip thing on your finger?

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I’m currently in hospital and was in the ICU yesterday and just thought about this late last night when I couldn’t sleep, because of being hooked up to the machines and all of the constant beeping.

I understand how they can measure your heartbeat, temperature, etc. with that, but was kind of confused on the oxygen saturation?

Does it check the skin coloration? I. E. how people with really low saturation can get blue fingertips?

In: 38

Oxygenated blood is a different colour to unoxygenated blood. The clip on your finger shines a bright light through your finger and measures it’s colour to determine how oxygenated it is.

They use the same sort of sensor that is on many sport watches to measure your heart rate.

The sensor sends a light pulse into your finger and measures the wavelength that bounces back. Built-in software then takes that reading and compares it to a pre-programmed calibration curve to determine your oxygen saturation.

You can use that information to calculate heart rate and breathing rate too, but the ICU has other gadgets that do that as well.

Edit – I know with sport watches they need to do testing on a range of skintones, since darker skin will absorb more light. But that’s more related to sensitivity than to the reading itself.