Assessment of the gas exchange function of the middle ear using nitrous oxide. A preliminary study

A method for assessing the gas exchange through the middle ear (ME) mucosa using nitrous oxide is introduced. Increases in the ME pressure was determined by a tympanogram or a micropressure sensor inserted into the mastoid cavity during ear surgery under general anesthesia using 67% nitrous oxide, 33% oxygen, and sevoflurane on 30 normal ears, 12 ears with otitis media with effusion (OME), and 3 postoperative ears with chronic adhesive otitis media or cholesteatoma. All the 30 normal ears except one showed varying pressure increase, and an inverse correlation was observed between pressure increase and area of mastoid on radiographs. Pressure increase was observed in 6 (50%) ears with OME, and this finding correlated well with the presence or absence of air space in the ME on computed tomography images examined preoperatively, on ears which had ear surgery, the presence or absence of pressure increase correlated with the degree of previous surgical intervention on the mastoid. The rationale and possibility of clinical application of this method is discussed.