[Effects of nitrous oxide on middle ear pressure]

Recent literature data suggest that permanent or reversible hearing loss may occur after general anesthesia. The etiology varies, while hearing loss following middle ear surgery is attributed to exposure to nitrous oxide (N,0). The objective of our study was to measure, using tympanometry, the middle air pressure change caused by nitrous oxide during general anesthesia and to establish its emetogenic effects during the postoperative period.

This academic (non-commercial) prospective study included two groups of patients (a total of 58), with ASA status I, II and III. The study group (n 30) consisted of patients undergoing unilateral ear surgery. In this group, the intratympanic pressure was measured in the unoperated (healthy) ear before and during the surgery. The control group (n 28) patients underwent nose, throat or neck surgical interventions. This group underwent measurement of bilateral intratympanic pressure in healthy ears, before and during the surgery. Both groups were operated under general balanced anesthesia. Pain, nausea and antiemetics were monitored during the first 24 postoperative hours. Statistical analysis was performed using the Mann-Whitney-Wilcoxon test.

This perioperative study confirmed the following: highly significant (p < 0.001) increase in intratympanic pressure in nonoperated ears in the study group and significant (p < 0.05) in controls. However, there was no statistical significance (p > 0.05) between groups. Pain was more freguent in controls, and nausea in the study group, but without significant difference (p > 0.05).

Postoperative audiometry findings showed no conductive or sensorineural hearing loss after interventions. Nitrous oxide can be used in general balanced anesthesia with discontinuation 15 to 45 minutes before insertion of the tvmpanic membrane and completion of middle ear surgery.