Colorimetric capnography is a qualitative measurement method that detects the presence of carbon dioxide (CO2, a relatively acidic gas) in a given gaseous environment.
Correct placement is evidenced by sufficient color change of the litmus paper while exposed to the airway gases which, if the device is properly placed, will contain relatively high amounts of exhaled CO2.
Detection of sufficient CO2 suggests that a patient is metabolically active and capable of eliminating CO2, while lack of color change or insufficient color change suggests an issue at one or more of many possible levels including issues with cellular metabolism, airway device integrity and placement, circuit integrity, mucous plugging, cardiopulmonary function, device malfunction, and more.
The colorimetric method rather presents CO2 simply as a color most commonly on the spectrum of purple (lower CO2) to gold (higher CO2) and leaves the clinician to interpret anything beyond this single returned value.
[6] There has been debate related to the term 'colorimetric capnography,' especially with the growing employment of this method during the COVID-19 pandemic due to an increased volume of patients requiring mechanical ventilation.