COMPLICATIONS OF NITROUS OXIDE ANESTHESIA FOR EAR SURGERY

Abstract

SUMMARY Middle ear pressure measured in surgical patients has been as high as 450 mm H2O after only 15 to 20 minutes of nitrous oxide inhalation. This increase in pressure bulges the eardrum outward and complicates otologic procedures such as replacement of the tympanic membrane or closing of a perforation. Increased middle ear pressure can also contribute to postoperative pain, delirium, nausea, and vomiting. Furthermore, discontinuation of nitrous oxide brings a decrease in middle ear pressure that can displace a tympanic graft. For all these reasons, many authors suggest avoiding nitrous oxide anesthesia for surgical procedures on the middle ear: tympanoplasty, stapedectomy, ossicular repositioning, and mastoidectomy. Finally, the possible lingering presence of nitrous oxide within the middle ear makes it wise to avoid nitrous oxide for all surgical patients who have middle ear disease and abnormalities of the eustachian tube. Because of the possibility of tympanic membrane rupture during or after nitrous oxide anesthesia, specific information concerning previous otologic surgery should be obtained prior to anesthesia. Patients especially vulnerable are those with acute or chronic middle ear infections or inflammation or scarring of the nasopharynx. Techniques that promote rapid recovery from anesthesia and the early return of pharyngeal reflexes facilitate venting of middle ear gas through the eustachian tube. The clinician can prevent the diffusion problem encountered with nitrous oxide by using a mixture of oxygen and air as the vaporizing vehicle for a more potent halogenated agent. If the anesthetist wants to use nitrous oxide, however, the lowest concentration feasible (50% or less) should be combined with a more potent agent for the shortest period possible and then discontinued as soon as the level of anesthesia is adequate.