Oximetry is a procedure for measuring the concentration of oxygen in the blood.

This is done using an oximeter, a photoelectric device specially designed for this purpose. A sensor is placed on a relatively thin part of the patient’s body, usually a fingertip or an earlob and red and infrared light is passed from one side to the other.

A pulse oximeter works by passing a beam of red and infrared light through a pulsating capillary bed. The ratio of red to infrared blood light transmitted gives a measure of the oxygen saturation of the blood.