![]() ![]() Phase IV: start of inhalation, CO 2 decreases to zero as atmospheric air enters the airway.This phase ends with a value of maximum CO 2 concentration Phase III: CO 2 concentration is relatively constant (reflects the concentration of CO 2 in the alveolar gas).Phase II: CO 2 increases rapidly as alveolar gas exits the airway.Phase I: start of exhalation, CO 2 concentration is initially zero.There is a similar shape for subjects with normal lung function.The width of the waveform depends on expiratory time.The amplitude of the waveform depends on EtCO 2 concentration.A maximum CO 2 is reached with each breath, corresponding to EtCO 2.The waveform shape always starts at zero and returns to zero.Whilst it is fairly easy to interpret numerical values for EtCO 2 and RR, interpretation of the waveform shape requires specific knowledge discussed below.Ī normal capnogram always has the following features: When monitoring End Tidal CO 2, there are 3 aspects to consider: the EtCO 2 value, the waveform shape and the respiratory rate (RR). The Microstream monitor has a rapid response time and may be used with both invasive and non-invasive ventilation. The newest type of EtCO 2 monitor is Microstream which uses molecular correlation spectrography for greater precision. But mainstream monitors increase mechanical dead space, depending on size of the chamber used to collect a gas sample, while adding weight on the airway, and can’t be used for non-invasive ventilation. This allows a more rapid response time and requires a smaller amount of sample gas than sidestream monitoring. Mainstream monitors have a sampling window which is inserted directly in-line with the ventilator circuit for CO 2 measurement. Sidestream monitors can be used with non-invasive ventilation. Gas samples are aspirated from exhaled gas flow via the ventilator circuit and are read at the monitor. Sidestream monitors rely on a separate monitor connected to the patient’s airway by a tube. There are 3 main types of End Tidal CO 2 monitors: sidestream, main¬stream, and Microstream. ![]()
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