Effect of Nitrous Oxide on Middle Ear Mechanics and Hearing Acuity

Abstract

Hearing loss was observed in a few patients following nitrous oxide anesthesia. The defect could result from changes in middle ear pressure incident to increased airway pressure and/or differential solubility of nitrous oxide and nitrogen. Consequently, we tested middle ear mechanics (Zwislocki Acoustic Bridge) and hearing acuity before, during and after breathing nitrous oxide and nonnitrous oxide mixtures, both with and without positive pharyngeal airway pressure. Decreased compliance and increased resistance occurred in all instances but was greater when nitrous oxide was present. Positive airway pressure appeared to be without effect. The observed changes persisted only in patients receiving N2O anesthesia for adenotonsillectomy. A conductive-type hearing loss of short duration was also noted in this group.