The effect of nitrous oxide on middle ear pressure in children during anaesthesia

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Abstract
Pressure changes in children with normal middle ears were studied under N2O anesthesia. The pre-anesthetic middle ear pressures ranged between +50 and -190 mm H2O. Middle ear pressure increased in all cases to a maximum pressure peak, at which a sudden drop in pressure occurred due to passive opening of the Eustachian tube. This pressure varied between +210 and +500 mm H2O. The pressure did not drop to the pre-anesthetic level. In all cases, in comparison with pre-anesthetic pressure values found 24 h after anesthesia, a definite decrease in pressure occurred with a reduction ranging from -30 to -400 mm H2O. Audiometric correlations between pre- and post-operative findings showed a decreased acuity in 9 patients, increased acuity in 6 patients and no significant change in 5 patients. Compliance results also showed no significant change between pre- and post-operative measurements. N2O raises the middle ear pressure until a level is attained which causes passive opening of the Eustachian tube. After the operation [24 h], even though the N2O is responsible for changes in middle ear mechanics which cause a mild conductive deafness in some patients, there is no significant change in overall acuity.