Prediction of post-operative middle ear pressure changes after general anaesthesia with nitrous oxide.

There has been a growing interest in the changes of pressure which occur in the middle ears of patients undergoing general anaesthesia. In this study the time course of middle ear pressure change was investigated in 38 adult E.N.T. patients scheduled for surgery under general anaesthesia with nitrous oxide. There was found to be a strong correlation between the magnitude of the post-operative middle ear pressure and the theoretical partial pressure of nitrous oxide within the middle ear cleft at the cessation of anaesthesia. The use of the mathematical model developed together with measurements of middle ear pressure taken for several minutes after intubation in any one patient allows prediction of the likely magnitude of the post-operative middle ear pressure change.