Currently available systems for breath-by-breath CO2 analysis include mass spectrometry and infrared light absorption. Mass spectrometry has a faster response time (about 100 ms) and the ability to analyze several gas concentrations simultaneously. However, its main drawback is its high price and costly maintenance. Infrared CO2 analyzers are cheaper and easier to use; each one is dedicated to a single patient, and the range of response times oscillates between 100 and 200 ms which is sufficient for breath-by-breath monitoring purposes. Two types of CO 2 analyzer based on the infrared radiation principle are available. Mainstream analyzers have the advantage of being part of the ventilatory circuit and exhibiting a very rapid response time. Sidestream analyzers pump the gas sample from the airway at a flow rate of 150 to 500 ml/min through a small tube to a remote analyzer. Their major disadvantages are obstruction of the tubing by pulmonary secretions or condensation and a slower response time than the mainstream analyzers (Hess 1990).
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