Break Through Inspiration During IPPV is Seen as “Curare Crest" in Sevograph

Background: The break through spontaneous effort in anaesthetized and ventilated patients is seen as ‘curarecleft’ during expiratory plateau phase of the capnography. At the open position of the sevoflurane vaporizer, the sevograph displays a mirror image graph to the capnograph. We studied the sevograph changes corresponding to ‘curare-cleft’ in capnography. Methods: We have observed that during break through spontaneous breaths the sevograph complemented ‘curare-crest’ corresponding to ‘curare-cleft’ in six patients. In second part of study 25 consenting adult patients coming for surgery were given general anaesthesia using fentanyl, propofol and suxamethonium. After tracheal intubation, controlled ventilation was started under sevoflurane anaesthesia. We allowed the onset of spontaneous effort and observed for the onset time to ‘curare-cleft’ in capnograph, ‘curare-crest’ in sevograph, visible negative deflection of the needle in airway pressure gauge till negative airway pressure of 5 cm H2O. The onset time for the both changes were statistically analysed for agreement analysis using Blend and Altman test. Results: ‘Curare-crest’ in sevograph was visible at the same breath in majority (76%) of instances along with that of ‘curare-cleft’ in capnograph. Both appeared in respective graphs significantly earlier than the negative deflection of airway gauge needle by 5 cm H2O and disappeared after vecuronium. Onset time for both ‘curare-cleft’ in capnograph and ‘curare-crest’ in sevograph had significant (p<0.01) correlation (R=0.97) too. Conclusions: The authors feel that both changes ‘curare-crest’ in sevograph complemented ‘curare-cleft’ in capnograph and can be equivocally used as warning signal for lighter planes of anesthesia or diminishing effect of muscle relaxant.