What is CO-oximetry?

The term CO-oximetry refers to devices that use at least four wavelengths of light to measure not only oxy and deoxy-hemoglobin, but also other forms of hemoglobin (e.g. CO-Hb, Met-Hb). While most conventional pulse oximeters use two wavelengths of light and can only detect oxyhemoglobin or deoxy-hemoglobin (to provide a functional saturation, sO2), some pulse oximeters contain many more wavelengths and the ability to function as ‘pulse CO-oximeters.’ With more wavelengths, these devices can measure dyshemoglobins and provide “fractional” oxygen saturation – see image below. (Note: these devices are clearly marked with this function and often are considerably more expensive than other devices). 

Despite this, the term ‘CO-oximeter’ is often used synonymously with ‘arterial blood gas analyzer’ because historically it was only multi-function arterial blood gas analyzers that possessed CO-oximetry functionality.  Some pulse CO-oximeters have ~10 wavelengths of light, whereas benchtop CO-oximeters may use 128 to 256 wavelengths of light.

Of note, the terms “CO-oximeter” and “Hemoxemeter” are brand names coined by the companies Instrumentation Laboratories and Radiometer, respectively. The generic term for a device with these capabilities is a “multi-wavelength oximeter,” but the term “CO-oximeter” is widely used to refer to these devices, regardless of brand.

Keywords: CO-oximetry, arterial, carboxyhemoglobin, methemoglobin