Capnometry

Capnometry is the measurement of the carbon dioxide (CO2) content in the breathing gas during the entire breathing cycle. Capnography refers to a continuous display of the capnometrically recorded CO2 curve on a monitor or permanent recording system.

The devices used for this purpose are called capnometers or capnographs, a displayed curve is called a capnogram.

Capnometry is mainly used to monitor respiratory patients in anaesthesia and intensive care. It provides information about the position and functional state of an endotracheal tube and allows the assessment of the metabolic situation and the quality of spontaneous breathing in both intubated and non-intubated patients.

Various physical methods can be used to measure the CO2 concentration. The currently most commonly used method is infrared spectrometry, also known as infrared spectrography or infrared spectroscopy.

The normal range of the partial pressure of CO2 in the expiratory air is 33-43 mm Hg, or with a CO2 content in the exhaled air of 4.3-5.7 vol%.