CARBON DIOXIDE ANALYSER

Typical Number in Hospital: 2

Cost Bands: 4

References:

Measurement of carbon dioxide in expired gases is important in lung function studies, and in intensive care where the expired carbon dioxide level may be used as a substitute for blood gas analysis, or to reduce the frequency at which blood sampling is required. The commonest method of carbon dioxide determination is by measuring the absorption of infrared light passing through the gas mixture. Sampling types exist, often using a Golay cell, but on-line (real time) analysers also exist which can produce graphical representation of the carbon dioxide variation during breathing or assisted ventilation.

The method is fast acting and accurate except for interference by the presence of other gases (e.g. carbon monoxide) and the accuracy is modified by the presence of different oxygen and nitrous oxide concentrations. These latter are often compensated for by setting controls on the main instrument. However, to make the necessary adjustments, some knowledge of the approximate levels of oxygen and nitrous oxide is required. See also Capnometer, and Infrared gas analyser.

Slower acting, and more accurate versions exist which include a moisture absorber.