Definition and notation of hemoglobin oxygen saturation.

Oxygen saturation (SO2) should not be confused with oxyhemoglobin fraction (FHbO2). As automated multiple wavelength photometers may yield both SO2 and FHbO2, care should be taken that only SO2 is used in checking the results of pulse oximeters. Arterial SO2 is the quantity aimed at by pulse oximeters. Although the accuracy of the measurement may be less than that of the analysis of an arterial blood sample in vitro, the measured quantity remains SO2. Using a special symbol, like SpO2, obscures this fact and should be discouraged.