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Designed, Produced, and maintained (Edition 10, March 2019) by 

Bhavani Shankar Kodali MD

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Derek FlahertyScotlandI have just set a test for our anaesthesia residents and asked them about the physical principles underlying measurement of CO2 in respired gases. All of them came back and described the Beer-Lambert Law. At first I thought they were just getting confused with pulse oximetry, but the more I mulled it over, the more I thought that the B-L law might actually be involved, and, on searching the web, a number of sites do say that the B-L law is used in capnography. However, the senior anaesthetists here continue to disagree - please can you clarify?