What is oxygen saturation?

Oxygen is carried in the blood attached to haemoglobin molecules. Oxygen saturation is a measure of how much oxygen the blood is carrying as a percentage of the maximum it could carry.

One haemoglobin molecule can carry a maximum of four molecules of oxygen, if a haemoglobin molecule is carrying three molecules of oxygen then it is carrying 3/4 or 75% of the maximum amount of oxygen it could carry.

One hundred haemoglobin molecules could together carry a maximum of 400 (100 x 4) oxygen molecules, if these 100 haemoglobin molecules were carrying 380 oxygen molecules they would be carrying (380 / 400) x 100 = 95% of the maximum number of oxygen molecules that could carry and so together would be 95% saturated.

Oxygen saturation is also refered to as SpO2.

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page last modified: 25/10/2005
Pulse oximetry
What is oxygen saturation?
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