Effect of anesthetic gas on middle ear fluid.

Tympanometry was performed before (preoperative) and after (intraoperative) the administration of inhalation anesthesia including nitrous oxide and halothane on 109 children undergoing myringotomy with pressure equalization tube insertion. A total of 213 preoperative tympanograms were compared with their intraoperative counterparts and the presence or absence of middle ear effusion at myringotomy. When preoperative tympanograms were consistent with pneumatized middle ears, intraoperative findings demonstrated a mean middle ear pressure increase of +147 daPa. When preoperative tympanometry suggested middle ear effusion, less than 1% demonstrated intraoperative tympanometric changes and/or findings at surgery that would support anesthesia clearing middle ear effusion. Preoperative tympanometric data were poor predictors of the presence or absence of effusion at myringotomy. The relationship between inhalation anesthetics (i.e., nitrous oxide and halothane) and middle ear fluids, and the reliability of tympanometry to predict middle ear effusion are discussed.