Describe the principles of measurement of end-tidal CO2, including the sources of 
error.

[Click here to toggle visibility of the answers]

College Answer

Candidates were expected to be detail the principles required to measure carbon dioxide in 
expired gas. This would involve some comment on ways to sample end tidal gas (in line vs side 
stream) and also ways to measure carbon dioxide. It was expected candidates could provide a 
detailed description of infrared analysis including the apparatus design and principles such as 
the asymmetric nature of CO2 as a polyatomic gas allowing absorption if infrared radiation with 
some discussion of response times and equipment design. It was expected these principles 
would be related to the potential errors (e.g. other gases, collision broadening).