A CO-oximeter is a device for detecting hypoxia

Hypoxia (medical)

Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...

, a medical condition relating to oxygen deficiency at tissue level.

The device measures absorption at several wavelengths to distinguish oxyhemoglobin from carboxyhemoglobin

Carboxyhemoglobin

Carboxyhemoglobin is a stable complex of carbon monoxide and hemoglobin that forms in red blood cells when carbon monoxide is inhaled or produced in normal metabolism. Large quantities of it hinder delivery of oxygen to the body...

 and determine the oxyhemoglobin saturation: the percentage of oxygenated Hb compared to the total amount of hemoglobin

Hemoglobin

Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates, with the exception of the fish family Channichthyidae, as well as the tissues of some invertebrates...

 (Hb), including carboxy-Hb, met-Hb, oxy-Hb, and reduced Hb. When a patient presents with carbon monoxide poisoning

Carbon monoxide poisoning

Carbon monoxide poisoning occurs after enough inhalation of carbon monoxide . Carbon monoxide is a toxic gas, but, being colorless, odorless, tasteless, and initially non-irritating, it is very difficult for people to detect...

 (CO), the CO-oximeter will detect this Hb and will report the oxyhemoglobin saturation as markedly reduced.

Measurement

Traditionally, this measurement is made from arterial blood

Arterial blood gas

An arterial blood gas is a blood test that is performed using blood from an artery. It involves puncturing an artery with a thin needle and syringe and drawing a small volume of blood. The most common puncture site is the radial artery at the wrist, but sometimes the femoral artery in the groin or...

 processed in a blood gas analyzer with a CO-oximeter. More recently, pulse CO-oximeters have made it possible to estimate carboxyhemoglobin with non-invasive technology similar to a Pulse oximeter

Pulse oximeter

A pulse oximeter is a medical device that indirectly monitors the oxygen saturation of a patient's blood and changes in blood volume in the skin, producing a photoplethysmograph. It is often attached to a medical monitor so staff can see a patient's oxygenation at all times...

. In contrast, the use of a standard pulse oximeter is not effective in the diagnosis of CO poisoning as patients suffering from carbon monoxide poisoning may have a normal oxygen saturation

Oxygen saturation

Oxygen saturation or dissolved oxygen is a relative measure of the amount of oxygen that is dissolved or carried in a given medium. It can be measured with a dissolved oxygen probe such as an oxygen sensor or an optode in liquid media, usually water.It has particular significance in medicine and...

reading on a pulse oximeter.