Inspiratory valve malfunction in a circle system: pitfalls in capnography

Capnography is a useful technique in monitoring the integrity of anaesthetic equipment such as the malfunctioning of unidirectional valves in circle system. However, the lack of a precise mechanism in existing capnographs to identify the start of inspiration and the beginning of expiration in the capnograms, makes the analysis of the carbon dioxide waveforms during inspiration difficult and thus results in inaccurate assessement of rebreathing. We report a case where, during the malfunction of the inspiratory unidirectional valve in the circle system, the capnograph failed to detect the presence of substantial rebreathing. Critical analysis of the capnogram recorded during the malfunction revealed that there was substantial rebreathing which was underestimated by the capnograph as it reports only the lowest CO2 concentration rebreathed during inspiration in such abnormal situations.(AU)

Maternal respiratory function during pregnancy

Maternal respiratory function in the second (26) and third (76) trimesters of pregnancy was measured in 102 women and showed that: (i) Thirty-eight per cent and 36 percent of the women in second and third trimesters respectively had FEV1.0 percent<75 percent. MTT 0.7 sec. (ii) Nineteen per cent and 29 percent of the women in the second and third trimesters respectively had MTT>0.7 sec. (iii) Pregnancy superimposed on previous respiratory disorders such as bronchial asthma potentiated the compromisation of both central and peripheral airway function in the third trimester in that 41 percent had FEV<75 percent and 34 percent MTT>0.7 sec. It is concluded that normal pregnancy does not significantly affect central and peripheral airway function. However, pregnancy in the presence of upper or lower respiratory tract disease may influence respiratory function negatively. (AU)