Editing Capnography (section)

== Working mechanism ==
{{see also|Carbon dioxide sensor}}
[[File:Capnometer-schema.jpg|thumb|Schematic overview of a capnograph|148x148px]]

Capnographs work on the principle that {{chem|CO|2}} is a polyatomic gas and therefore absorbs [[Infrared|infrared radiation]]. A beam of infrared light is passed across the gas sample to fall on a sensor. The presence of {{chem|CO|2}} in the gas leads to a reduction in the amount of light falling on the sensor, which changes the voltage in a circuit. The analysis is rapid and accurate, but the presence of [[nitrous oxide]] in the gas mix changes the infrared absorption via the phenomenon of collision broadening.<ref>{{cite journal|vauthors=Raemer DB, Calalang I|date=April 1991|title=Accuracy of end-tidal carbon dioxide tension analyzers|journal=J Clin Monit|volume=7|issue=2|pages=195–208|doi=10.1007/BF01618124|pmid=1906531|s2cid=33836449 |doi-access=free}}</ref> This must be corrected for measuring the {{chem|CO|2}} in human breath by measuring its infrared absorptive power. This was established as a reliable technique by [[John Tyndall]] in 1864, though 19th and early 20th century devices were too cumbersome for everyday clinical use.<ref>{{cite journal|author=Jaffe MB|date=September 2008|title=Infrared measurement of carbon dioxide in the human breath: "breathe-through" devices from Tyndall to the present day|journal=Anesth. Analg.|volume=107|issue=3|pages=890–904|doi=10.1213/ane.0b013e31817ee3b3|pmid=18713902|s2cid=15610449 |doi-access=free}}</ref> Today, technologies have since improved and are able to measure the values of {{chem|CO|2}} near instantaneously and has become a standard practice in medical settings. There are currently two main types of {{chem|CO|2}} sensors that are used in clinical practice: main-stream sensors and side-stream sensors. Both effectively serve the same function to quantify the amount of {{chem|CO|2}} that is being exhaled in each breath.