The Relational Change between Middle Ear Internal Pressure and Mucosa of Mastoid Area during both N₂O Inhalation and Wash out

Abstract

Nitrous oxide (N₂O) is known to cause an increase in volume and/or pressure in enclosed body cavities as a result of diffusion. In the middle ear cavity, both the middle ear pressure (MEP) and volume increase due to the semicompliant boundaries of this region which include the tympanic membrane and eustachian tube. During general inhalational anesthesia, it seemed that the functions were quickly passive ventilation and comfortable ventilation through the mucosa of the mastoid area. This study examined the relation of the mastoid area and MEP under the start and cessation of N₂O.
During general anesthesia with or without N₂O, it seemed that the increase (10.7±2.1mmH₂O•min^-1) or decrease (2.1±0.5mmH₂O•min^-1) in MEP without passive ventilation was related to very low circulation in the mastoid area (MEP during N₂O administration and the area: r=0.55 (p=0.03); MEP during N₂O wash out and the area: r=0.73 (p=0.02)).
Based on the present results, we observed a positive correlation between the changes of MEP in the mastoid area.