Abstract
This thesis documents the effect of anaesthetic and analgesic drugs on oesophageal and
gastric pressures in the dog and cat. In particular the lower oesophageal sphincter
pressure, gastric pressure and derived pressure-'Barrier Pressure'were determined.
A review of clinical cases of post-anaesthetic oesophagitis and stricture formation in
dogs and cats seen at Bristol 1973-1990 reveal that the disease was found in 10 dogs and
8 cats within this period of which only 2 dogs and 2 cats survived, the rest of the animals
either died or were euthanased. 'Immobilon' (etorphine hydrochloride with
methotrimeperazine or acepromazine) in dogs and 'Saffan' (alphaxalone-alphadolone) in
cats seemed to be the most important anaesthetic causes of this condition.
The studies were carried out using a non-perfused manometry system utilizing
catheter with subminiature strain gauge pressure transducers embedded at its tip..
a
An accurate correlation between the external length from the lower jaw incisor tooth to
the anterior border of the head of the 10th rib and the internal length of the oesophagus
from the lower jaw incisor tooth to the lower oesophageal sphincter was determined in 50
dogs and 50 cats utilizing radiography.
In all studies were carried out on 139 dogs and 112 cats.
In dogs, all the sedatives used (atropine, pethidine and acepromazine) decreased lower
oesophageal sphincter pressure and barrier pressure but there were no significant
differences between the combinations used and propofol caused a greater decrease in
lower oesophageal sphincter pressure and barrier pressure compared to thiopentone. In
dogs lower oesophageal sphincter pressure and barrier pressure was less well maintained
with isoflurane compared to halothane. In this species pressures were relatively well
maintained in the right lateral recumbency-head horizontal position compared to a dorsal
recumbency-head horizontal position. Metoclopramide seemed effective at maintaining a
better barrier pressure but only if given before sedation, it was not effective if its
administration was delayed.
In cats, atropine alone or in combination caused a marked decrease in both lower
oesophageal sphincter pressure and barrier pressure; Alphaxalone-alphadolone (Saffan)
produced a most dramatic decrease of these pressures whereas were best maintained with
ketamine either alone or in combination with xylazine.
In both dogs and cats the lower oesophageal sphincter pressure and barrier pressure fell
progressively during anaesthesia but surgical stimulation tended to reverse this decreased
lower oesophageal sphincter tone. A long duration of anaesthesia seemed to decrease
lower oesophageal sphincter tone by the cumulative depressant effects of the volatile
anaesthetic agents.