A COMPARISON OF THE EFFECTS OF HALOTHANE AND ISOFLURANE IN COMBINATION WITH NITROUS-OXIDE ON LOWER ESOPHAGEAL SPHINCTER PRESSURE AND BARRIER PRESSURE IN ANESTHETIZED DOGS

The effects of surgery, and of halothane and isoflurane, on oesophagea l pressures were examined in 30 dogs. The dogs were premedicated with a combination of acepromazine maleate (0.1 mg/kg) and pethidine hydroc hloride (1 mg/kg), and anaesthesia was induced with thiopentone (10 mg /kg), Ten of the dogs underwent abdominal surgery with halothane, 10 u nderwent abdominal surgery,vith isoflurane and 10 underwent non-abdomi nal surgery with halothane. Gastric pressure, lower oesophageal sphinc ter pressure and oesophageal barrier pressures were measured at five t o 10 minutes after induction, five to 10 minutes after the initial sur gical incision, during the abdominal surgery and while the skin was be ing sutured. There were no significant differences in lower oesophagea l sphincter pressure between the groups of dogs but the pressures were greater in all the dogs during the surgical manipulation than shortly after induction or white the skin was being sutured. During abdominal surgery with halothane the barrier pressure was significantly higher (P<0.05) than during non-abdominal surgery with halothane, The barrier pressure was lower (P<0.001) during skin suturing after abdominal sur gery with isoflurane than after abdominal or non-abdominal surgery wit h halothane. The lower oesophageal sphincter appears to be more sensit ive to isoflurane than halothane.