Lippencott's Nursing Center states that SpO2, or pulse oximetry, is normal when in the range of 97 to 99 percent. Pulse oximetry measures the rate of arterial oxygen saturation.
Lippencott's Nursing Center further states that the effect of a low arterial oxygen saturation can come before some noticeable signs of respiratory distress, such as lethargy, cyanosis and agitation. Reading SpO2 levels is done by determining how much red and infrared light are absorbed by a pulsating capillary. Readings between 95 and 99 are considered to be well within the guidelines for a normal reading, and only if readings are under this do doctors check for respiratory distress.