Designed, Produced and maintained by

Bhavani Shankar Kodali MD


Physics of capnography

Bhavani Shankar Kodali MD


Factors affecting IR Spectrography



Oxygen does not absorb IR light




How does oxygen affect CO2 measurements?

Oxygen does not absorb IR light
Oxygen produces collision broadening phenomena that can cause falsely low CO2 measurements.


Although oxygen does not absorb IR light it may indirectly affect the absorption by C02 by collision with the C02 molecules and broadening the absorption peak. While it does not cause as large an effect as N20, oxygen causes a falsely low C02 reading. Some units automatically correct or have a user-actuated electronic offset for the concentration oxygen encountered.1


1. Carbon dioxide monitors. Health Devices 1986;15:255-85.

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