Blood oxygen level is measured using pulse oximetry, a noninvasive procedure designed to monitor the delivery of oxygen to peripheral tissue, says Johns Hopkins Medicine. Pulse oximetry uses hemoglobin coloration and blood flow pulsation to measure the blood oxygen level.
To measure the oxygen level of the blood, a pulse oximetry device monitors highly oxygenated and less oxygenated blood and works out the difference, explains Johns Hopkins Medicine. First, a probe is attached to a finger or other small part of the body. It uses a light source and a light detector located on opposite sides of the body part to measure the amount of oxygen-rich blood. Hemoglobin without oxygen absorbs a greater part of the red light coming from the device, while hemoglobin rich in oxygen absorbs more of the infrared light. The light detector assesses the amount of each type of light. The difference between them corresponds to the level of blood oxygenation, which the device calculates and displays.
Pulse oximetry is a painless and noninvasive procedure, and as such carries no significant risks, Johns Hopkins Medicine notes. Wearing the device for extended periods may harm the tissue, and the adhesive used may irritate the skin in some cases, but there are no other risks.