Middle ear pressure variation: effect of nitrous oxide

Previous studies examining middle ear pressure changes due to inhalant anesthesia, including nitrous oxide, have cited equivocal results. An investigation was performed to closely monitor changes in middle ear pressure during middle ear surgery. Baseline tympanometry was performed before anesthesia, and middle ear pressure was then documented in 1-min time intervals. A total of 97 subjects were studied; 51 received nitrous oxide and halothane, and 46 received halothane alone. Results indicate that nitrous oxide causes significantly greater pressure fluctuations than halothane alone. There were no effects for time of surgery, type of fluid, or baseline. Pressure fluctuation was attributed to eustachian tube function. Case studies are presented to demonstrate subject variability, and suggestions for validation study procedures are presented.