Oxygen Saturation Calculation Formula

Oxygen saturation (SpO2) monitoring via pulse oximetry is standard practice in NICUs. Pulse oximeters work on the principle that saturated hemoglobin (oxyhemoglobin) is a different color from desaturated hemoglobin (deoxyhemoglobin) and thus absorbs light of a different frequency.

The functional oxygen saturation measured by pulse oximeters is represented by the equation:

 100 × OxyHb/(OxyHb + DeoxyHb), 

Where, OxyHb is oxyhemoglobin and DeoxyHb is deoxyhemoglobin.

In general, pulse oximeters provide excellent data about oxygenation in the physiologic range, but there are important limitations that should be considered. The calculation of saturation is dependent on sensing light so that ambient light striking the sensor can lead to a false reading.

Oxygen Saturation Estimate from PO2

This modified Hill equation produces an excellent estimation of O2 Saturation, closely mirroring the standard dissociation curve for human blood.

Oxygen Saturation = 100 / [1 + {23400 / (PO2^3 + (150 × PO2))}]

Where, PO2 = partial pressure of oxygen.

This equation is appropriate for saturation estimates when blood pH is 7.4 blood temperature is 37° C.


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