Changes in respiratory pattern during induction of anaesthesia with sevoflurane: comparison of nasal and the oral breathing.

In order to test the hypothesis that the effects on ventilation of nasal inhalation of sevoflurane during induction of anaesthesia differ from those of oral inhalation, 20 patients underwent inhalation induction of anaesthesia with sevoflurane 5% either through the nasal route or the oral route. In 10 patients who breathed through the nose (N-group), there was an immediate decrease in tidal volume with no change in respiratory duration whereas no similar change was observed in the 10 patients who breathed through the mouth (O-group). The time from the start of sevoflurane inhalation to the onset of sleep was significantly shorter in the O-group compared with the N-group [86.2 +/- 4.4 (mean +/- SE) vs. 115.0 +/- 8.4 sec, P < 0.01].