Effect of anesthetic gases on middle ear pressure in the presence of effusion.

Halothane, randomly with or without nitrous oxide (N2O), was administered by face mask to 69 children (selected by tympanometric and otoscopic evidence of chronic otitis media with effusion) for pressure equalization (PE) tube insertion in one or both ears. Tympanograms were obtained from 127 ears prior to and soon after the induction of a satisfactory level of anesthesia. The effect of anesthesia was identical whether N2O was used or not: 85% (75/88) of ears with flat tympanograms (B) remained B (all contained fluid); 15% (13/88) became peaked and 62% (8/13) of those contained fluid. All but two ears with peaked tympanograms showed substantial increases in middle ear pressure (mean: 179 mm H2O, range: -70 to +550 mm H2O) regardless of the presence of fluid. We conclude the N2O is not responsible for aerating the middle ear in the usual surgical setting, and that assisted ventilation used in mask inhalation anesthetic techniques will inflate all normal middle ears, most ears with a peaked tympanogram regardless of fluid, and 15% of ears with a nonpeaked tympanogram. It is unlikely that inhalation of anesthetic gases is responsible for displacement of middle ear fluid down the eustachian tube within the time constraints of the usual operating room setting.