[Gas diffusion in the middle ear during anesthesia for tympanoplasty]

The problems of diffusion of gas into the middle ear during anaesthesia have been described by several authors since 1965. The administration of anaesthetic concentrations of nitrous oxide raises middle ear pressure in the order of 3.43 to 3.92 kPa (350 to 400 mm H2O). This phenomenon disappears spontaneously after cessation of nitrous oxide anaesthesia and causes no trouble except a few cases of deafness and some rare tympanic ruptures. We have tried to solve this problem during anaesthesia for tympanoplasty by substituting air for nitrous oxide and by the use of ethrane as basic anaesthetic agent. Anaesthesia was potentiated by narcotics and the patients were adequately curarized. The results showed that this technique greatly reduced diffusion of gases if we kept the PaO2 under 17.9 kPa (135 mm Hg) and the PaCO2 at 3.9 kPa (30 mm Hg). Controls have shown that diffusion is greater with higher PaCO2. Middle ear pressure, measured with Madsen impedence-meter, was not higher than 0.68 kPa (70 mmn H2O).