If an inhalation agent has an odor that causes airway irritation and cardiovascular instability, it is important that inhalation induction is performed rapidly and smoothly. So, we studied characteristics of inhalational induction in healthy adults using high inspired concentrations of sevoflurane.

Fifty-three patients, 19 to 59 years old, received 6 vol% sevoflurane in 66 vol%N₂O/28 vol%O₂ by face mask for five minutes until endotracheal intubation. Participants exhaled to residual volume and took vital capacity breaths of the gas mixture, thereafter ventilation was manually assisted. Subsequently we recorded the number of breaths before apnea, time to loss of consciousness, the loss of lid-lash reflex, eyeball deviation, the time until BIS reduced to 45, degree of jaw relaxation, and vital signs. After endotracheal intubation without muscle relaxant, ease of intubation and vital signs were observed.

Apnea developed after an average three time vital capacity breaths, time to unconciousness was less than one minute. The mean times to loss of lid-lash reflex was 69.0 ± 8.2 seconds, to eyeball deviation 85.7 ± 22.2 seconds, and to pupil convergenece 239.5 ± 31.4 seconds. There was no case of increased secretion or laryngospasm during mask ventilation. The BIS score was significantly lowered after inhalational induction, and the time to a BIS < 45 was 132.3 ± 19.7 seconds. Mean blood pressures before and after intubation were 75.0 mmHg, and 104.6 mmHg, and heart rates before and after intubation were 77.0 beats/min and 109.8 beats/min, respectively.

The speed of the induction of anesthesia to loss of lid lash reflex in healthy adults approaches that of intravenous induction techniques. No untoward airway responses were noted using the vital capacity breath technique. Healthy adults were successfully intubated with sevoflurane without muscle relaxant.