Upper oesophageal sphincter function during general anaesthesia.

The effect of anaesthesia on the upper oesophageal sphincter response to acid in the distal oesophagus and hypopharynx, and the effect of atracurium besylate on acid migration into the hypopharynx, was studied in 102 patients undergoing elective varicose vein surgery. Group 1 (n = 48) received a general anaesthetic and the muscle relaxant atracurium besylate whereas group 2 (n = 54) received a general anaesthetic without relaxation. Upper oesophageal sphincter tone was significantly lower in patients receiving muscle relaxants ('sphinctometer output', eight versus 14, P < 0.05). Sixteen patients (16 per cent) had reflux into the distal oesophagus during anaesthesia (nine in group 1 and seven in group 2, P not significant), of whom seven had reflux to the hypopharynx. There was no difference in incidence of hypopharyngeal acid exposure between groups. Upper oesophageal sphincter tone did not alter in response to reflux into the distal oesophagus or hypopharynx in either group. The upper oesophageal sphincter fails to protect the hypopharynx under general anaesthesia even if patients do not receive a muscle relaxant.