Analysis of CO2 waveforms:
Prolongation phase II and III:
Prolongation or slanting of the expiratory upstroke phase II occurs when there is obstruction to expiratory gas flow (e.g., asthma, bronchospasm, obstructive pulmonary disease, and kinked endotracheal tube,1-9 or in the presence of leaks in the breathing system.10 A sidetream capnograph may allow gas mixing within the sampling tube (dispersion) if sampling rate is slow (50 ml.min-l) or if the tubing is too long or has too wide a bore, or both. Such dispersion of gases can also result in prolongation of the expiratory upstroke.11-13 The slope of the expiratory plateau (phase III) can be increased during pregnancy as a normal physiological variation.5,14 Besides, it can also result from factors that produce obstruction to expiratory gas flow which may also result in a prolonged phaseII.1-9
| Non Pregnant || Capnogram during cesarean section |
(The slope the expiratory plateau is increased as a normal physiological variation in pregnancy)
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|Normal|| Airway obstruction (eg., bronchospasm). Phase II and phase III are prolonged and alpha angle (angle between phase II and phase III) is increased |
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|Normal||Capnograms recorded with prolonged response time (Base line is elevated, prolongation of phase II and III, prolongation of inspiratory descending limb)|
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A dip in the plateau (curare cleft) indicates a spontaneous respiratory effort during mechanical ventilation.5,8,10
| Curare cleft|
A dip in the plateau indicates spontaneous respiratory effort
It can also result from surgical manipulations in abdomen
Terminal dip of alveolar plateau: Dilution of PETCO2 by fresh gas flow (FGF) in circuits and ventilators using a continuous flow may result in the dilution of expired gases by the FGF’s producing a terminal dip in alveolar plateau. This results in falsely low PETCO2 values.
|Normal||Dilution of PETCO2 by fresh gas flow (use of PEEP or CPAP in IMV bird ventilators, can also occur as a result of dilution of expired gases by FGF in rebreathing circuits)|
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