PULSE OXIMETRY or SaO2 - This is a non-invasive measure of one's oxygen saturation; that is, the amount of oxygen saturated in one's hemoglobin in terms of a percentage. This is not as accurate as the values obtained from a blood sample and should only be used as a gauge of one's oxygenation. Normal ranges are between 95-100%. Supplemental oxygen is not generally instituted unless SaO2 is less than 88-90% at rest.

Pulse oximetry is based on two principles: that oxyhemoglobin and deoxyhemoglobin differ in their absorption of red and infrared light (that is spectrophotometry), and that volume of arterial blood in tissue (and hence, light absorption by the blood) changes during the pulse (that is plethysmography).

A pulse oximeter determines SpO2 by sending red and infrared light into a blood vessel bed and measuring changes in light absorption during the pulsatile cycle. Red and infrared low-voltage Light Emitting Diodes (LEDs) in the oximetry sensor serve as light sources, a photodiode serves as photo detector. Because oxyhemoglobin and deoxyhemoglobin differ in light absorption, the amount of red and infrared light absorbed by blood is related to hemoglobin and oxygen saturation.

To identify the oxygen saturation of the arterial hemoglobin, the sensor uses the pulsatile nature of arterial flow. During systole, a new pulse of arterial blood enters the vascular bed, and blood volume and light absorption increases. During diastole, the blood volume and light absorption reach their lowest point. The sensor bases its SpO2 measurements on the difference between maximum and minimum absorption (that is measurements at systole and diastole). By this means, it focuses on light absorption by pulsatile arterial blood, eliminating the effects of nonpulsatile absorbers such as tissue, bone, and venous blood.