Capnometers.

Abstract

The process of monitoring carbon dioxide in the respired gas is described. The physical principle employed in many capnometers is nondispersive infrared absorption: An infrared light beam is projected through a gas sample and the intensity of transmitted light is measured. Differentiation between sidestream and mainstream capnometers is made, where appropriate, in the description of this process. Important factors such as sampling flow rate, water removal, exhaust gas scavenging, measurement interference, calibration, the effect of water vapor, and measurement chamber cleaning are described as part of this process. The value of the data displayed, once derived, is based on the knowledge that carbon dioxide is an end product of the metabolism of oxygen-consuming organisms. The data can be a useful indicator of metabolic, circulatory, and ventilatory processes.