UPPER ESOPHAGEAL SPHINCTER PRESSURE AND THE INTRAVENOUS INDUCTION OF ANESTHESIA

The upper oesophageal sphincter can prevent regurgitation of oesophageal contents into the pharynx following gastro‐oesophageal reflux in the awake patient. Upper oesophageal sphincter pressure was recorded with a Dent sleeve after hypnosis with midazolam (n = 7) and also during the rapid intravenous induction of anaesthesia with thiopentone (n = 16) or ketamine (n = 7). Thiopentone decreased mean(SD) sphincter pressure from an awake value of 43(19) to 9(7) mmHg (p < 0.001) and midazolam from 38(25) to 7(3) mmHg (p<0.02). Mean(SD) sphincter pressures before and after ketamine were not significantly different at 29(15) and 32(21) mmHg respectively. After suxamethonium mean(SD) sphincter pressure in all patients (n = 30) was 7(4) mmHg. Laryngoscopy (n = 30) caused a small increase in mean(SD) sphincter pressure to 13(10) mmHg (p < 0.001). Thiopentone caused a rapid fall in upper oesophageal sphincter pressure which usually started before loss of consciousness. These findings have implications for the timing of cricoid pressure application. Copyright © 1992, Wiley Blackwell. All rights reserved