[Evaluation of tympanometric alterations in patients subject to general anesthesia with nitrous oxide]

The nitrous oxide is an inhaling gas that can increase intratympanic pressure during the anesthetic act and cause negative pressure after it is discontinued, mainly in patients with Eustachian tube dysfunction. These pressure variations may come up with clinical implications such as tympanic membrane rupture, ossicular system disarticulation, haemotympanum, barotraumas, prosthesis displacement stapaedotomy and tympanic graft lateralization after tympanoplasty, in addition to serous fluid entrance into the middle ear during the negative pressure phase.

To evaluate the nitrous oxide influence on the middle ear pressure in a population without tube malfunction performing pre and postoperative tympanometry.

Transversal cohort.

A prospective study was carried out with Universitário Clementino Fraga Filho Hospital- UFRJ intern patients, subject to general anesthesia with the use of 50% nitrous oxide from April to June 2003. It was also evaluated whether the duration of surgery, associated anesthetics, presence of allergic rhinitis and nasal septal deviation could contribute to the appearing of intratympanic pressure alteration.

The sample is made up of 50 patients, in almost half of them (48%), postoperative tympanometry alterations (type C curve) were found, when comparing to the preoperative tympanometric control (type A curve). Neither sex nor age interfered in the appearing of tympanometry alterations during the post operative as well as the surgery timing. The anesthetic type volatile associate, nasal septal deviation and allergic rhinitis were not able to influence during the postoperative middle ear pressure.

The nitrous oxide modifies intratympanic pressure during the anesthetic act as well as after it was discontinued.