University of Thessaly, Faculty of Veterinary Medicine, Clinic of Surgery, Karditsa, Greece Gastro-Oesophageal Re¯ux during Thiopentone or Propofol Anaesthesia in the Cat A. D. GALATOS 1,3 , I. S AVAS 2 , N. N. PRASSINOS 1 and D.RAPTOPOULOS 2 Addresses of authors: 1 University of Thessaly, Faculty of Veterinary Medicine, Clinic of Surgery, PO Box 199, GR-43100 Karditsa; 2 Aristotle University of Thessaloniki, Faculty of Veterinary Medicine, Clinic of Surgery, 11 St. Voutyra Street, GR-54627 Thessaloniki, Greece; 3 Corresponding author With 3 tables (Received for publication September 14, 2000) Summary Lower oesophageal pH was monitored in 50 cats anaesthetized with either thiopentone or propofol. Gastro-oesophageal re¯ux,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-signi®cant. Re¯ux usually occurred shortly after the induction of anaesthesia and had a mean duration of about 23 min. The re¯uxate was always acidic (pH < 4.0). Gastric contents of below 2.5 were re¯uxed on three occasions, two in the thiopentone group and one in the propofol group.Regurgitation and ¯ow of gastric contents from the mouth occurred in only one cat anaesthetized with propofol. None of the cats that exhibited re¯ux developed any signs of post- anaesthetic oesophagitis or stricture formation. Introduction Gastro-oesophageal re¯ux (GOR) during anaesthesia is the most common cause of severe oesophagitis and stricture formation in the cat and dog (Tams, 1996; Bennett and Pascoe, 1999). It appears that the lower oesophageal sphincter (LOS) plays a key role in the prevention of re¯ux (Hardy, 1988), and many drugs used in anaesthesia have been reported to reduce LOS pressure (LOSP) and barrier pressure (BrP), i.e.the difference between LOSP and gastric pressure (Strombeck and Harrold, 1985; Hallet al.,1987; Hashim and Waterman, 1991, 1993; Waterman and Hashim, 1992; Hashim et al., 1995; Bennett and Pascoe, 1999). However, reduction of LOSP or BrP only gives an indication of whether re¯ux may occur. The effect of pre-medication on the incidence of GOR in the anaesthetized dog has been reported (Galatos and Raptopoulos, 1995a). Furthermore, studies in dogs have shown thathe greatereduction of LOSP and BrP caused bypropofolthan by thiopentone (Waterman and Hashim, 1992) correlates with a higher incidence of GOR during anaesthesia induced with propofol than with thiopentone (Raptopoulos and Galatos, 1997) in this species. Because the reverse situation has been reported in the cat, i.e.propofol decreased LOSP and BrP less than thiopentone (Hashim and Waterman, 1991), one could speculate that the incidence of GOR may be expected to be higher during thiopentone than during propofol anaesthesia in the cat. Furthermore, the auth are notaware of any report on the incidence of GOR in the anaesthetized cat, whose J. Vet.Med.A 48, 287±294 (2001) Ó 2001 Blackwell Wissenschafts-Verlag, Berlin ISSN 0931±184X U. S.Copyright Clearance Center Code Statement: 0931±184X/2001/4805±0287 $15.00/0 www.blackwell.de/synergy