Gastro-oesophageal reflux during anaesthesia induced with either thiopentone or propofol in the dog

Lower oesophageal pH was monitored in 68 dogs under anaesthesia induced with either thiopentone or propofol and maintained with halothane in oxygen. 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 17.6% (6/34) and 50% (17/34) of the thiopentone-induced and the propofol-induced dogs, respectively, the difference between the 2 groups being significant. Reflux usually occurred shortly after the induction of anaesthesia and had a mean duration of about 46 min. On most occasions, in both groups, the refluxate was acid (pH < 4.0), and in only 2 cases in each group, it was alkaline (pH > 7.5). Gastric contents of pH below 2.5 were refluxed on 7 and 2 occasions in the propofol and the thiopentone group, respectively. Regurgitation occurred in only 2 dogs, one in each group. It was concluded that the higher incidence of reflux in the propofol-induced dogs may have been due to the greater decrease of lower oesophageal sphincter pressure induced by propofol than by thiopentone in dogs.