Anesthetic and respiratory gas measurements by infrared technology.

Infrared systems for measuring respiratory gas are accurate, stable, and reliable, and cover most respiratory gases. Their most serious limitations (requiring complementary analyzers) are their inabilities to measure O2 (to assure a safe inspired O2) and nitrogen (for clinical N2 washout and detection of air emboli). Properly designed IR systems can monitor higher breath rates, are smaller, require less power, and are less costly than time-shared mass spectrometers. IR systems have a multitude of interfering factors that affect absorption, but control and analysis systems can compensate for them. IR technology continues to advance, with its most recent enhancement being the ability to identify the anesthetic agent in use. Mass spectrometers and Raman analyzers, which have more comprehensive capabilities, will not render IR technology obsolete until they can meet IR technology levels for cost, size, and reliability.