Upper oesophageal sphincter pressure during inhalational anaesthesia.

Upper oesophageal sphincter pressure was recorded with a Dent sleeve in 30 patients breathing nitrous oxide, oxygen and halothane. Twenty-three patients, after thiopentone induction, received suxamethonium and had their trachea intubated either before (group A, n = 11), or after (group B, n = 11), a study period of inhalational anaesthesia. Group C (n = 8) received an inhalational induction. Mean (SD) sphincter pressure after loss of consciousness was 8 (7) mmHg (group A), 6 (5) mmHg (group B) and 24 (13) mmHg (group C) increasing to 19 (7) mmHg in group A immediately after intubation. With an end-tidal halothane concentration of 1.5%, mean sphincter pressure in group B, 16 (7) mmHg, was significantly lower than in group A, 45 (21) mmHg (p < 0.001) and group C, 27 (14) mmHg (p < 0.05). Halothane had no dose-related effect on sphincter pressure. Insertion of a laryngeal mask in group C (n = 7) had no significant effect on sphincter pressure. Induction and maintenance of anaesthesia with halothane, unlike thiopentone or suxamethonium, maintained a degree of upper oesophageal sphincter tone, although three patients in this study had sphincter pressures of less than 10 mmHg and would therefore have been at risk of regurgitation in the presence of gastro-oesophageal reflux.