Capnography

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Capnography is the monitoring of the concentration or partial pressure of carbon dioxide (CO₂) in the respiratory gases. Its main development has been as a monitoring tool for use during anaesthesia and intensive care. It is usually presented as a graph of expiratoryCO₂ plotted against time, or, less commonly, but more usefully, expired volume. The plot may also show the inspired CO₂, which is of interest when rebreathing systems are being used.

Capnogram: a typical capnogram is shown above. During inspiration the CO2 tension should be neligible unless there is rebreathing. Dead space gas is exhaled first, it contains no CO2, and is followed by alveolar gas and a rapid rise in CO2 which reaches a clear plateau in normal lungs and is termed the end-tidal CO2 tension. 

Image source: http://www.frca.co.uk/article.aspx?articleid=100389

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