The formula for pulse oximetry calculates the arterial oxygen saturation (SaO2), representing the percentage of hemoglobin in the blood that is saturated with oxygen. It is expressed as:
SaO2 = [HbO2] / ([HbO2] + [Hb])
Where:
- SaO2 is the arterial oxygen saturation.
- [HbO2] is the concentration of oxygenated hemoglobin.
- [Hb] is the concentration of deoxygenated hemoglobin.
In simpler terms, the formula divides the amount of hemoglobin carrying oxygen by the total amount of hemoglobin in the blood. This ratio is then expressed as a percentage, giving the SaO2 reading.
Pulse oximetry devices estimate SaO2 non-invasively by shining red and infrared light through a pulsating capillary bed (typically a fingertip, toe, or earlobe) and measuring the absorbance of these wavelengths. Oxygenated and deoxygenated hemoglobin absorb these wavelengths differently, allowing the device to estimate the ratio used in the formula.
