Pulse Oximetry versus Co-oximetry: What’s the Difference?

Pulse oximeters and co-oximeters are both used to determine trends in a patient's blood oxygen saturation levels and are intended to warn clinicians of abnormal saturation levels. These devices, however, are used to measure different blood parameters and utilize slightly different techniques for measurement.

Pulse oximeters are noninvasive diagnostic devices that continuously estimate the oxygen saturation of hemoglobin in a patient's arterial blood (SpO2). A pulse oximeter uses a sensor and/or a probe to measure SpO2, which represents functional oxygen saturation. This is the ratio of oxygenated hemoglobin (hemoglobin that is carrying oxygen O2Hb) to functional hemoglobin (hemoglobin that is capable of carrying oxygen). The operation of these instruments is based on measuring light absorbance changes resulting from arterial blood flow pulsations. These oximeters include red and infrared light sources (typically LEDs), photodetectors, and probes that transmit light through a pulsating arterial bed, such as the fingertip, earlobe, or toe.

A co-oximeter, on the other hand, is invasive and uses a blood sample to measure a different value: SaO2, which represents fractional oxygen saturation. This is the ratio of oxygenated hemoglobin to total hemoglobin. The SaO2 measurement takes into account dysfunctional hemoglobin (hemoglobin that cannot carry oxygen, also called dyshemoglobin), which the pulse oximeter measurement does not. Co-oximeters provide...