Gastro-oesophageal reflux during thiopentone or propofol anaesthesia in the cat

Lower oesophageal pH was monitored in 50 cats anaesthetized with either thiopentone or propofol. Gastro-oesophageal reflux, as evidenced by a decrease in lower oesophageal pH to less than 4.0 or an increase to more than 7.5, occurred in 16 % (4/25) and 12 % (3/25) of the cats anaesthetized with thiopentone and propofol, respectively, the difference between the two groups being non-significant. Reflux usually occurred shortly after the induction of anaesthesia and had a mean duration of about 23 min. The refluxate was always acidic (pH < 4.0). Gastric contents of pH below 2.5 were refluxed on three occasions, two in the thiopentone group and one in the propofol group. Regurgitation and flow of gastric contents from the mouth occurred in only one cat anaesthetized with propofol. None of the cats that exhibited reflux developed any signs of post-anaesthetic oesophagitis or stricture formation.