Gastro-oesophageal reflux is a serious problem associated with
ruminant anaesthesia. The results of the present investigation of
this problem are summarised below.
Management of animals prior to and during anaesthesia influenced the incidence of reflux. Depriving the sheep of food and
water for 24 hours prior to induction of anaesthesia significantly
reduced the incidence of reflux. The occurrence of reflux was also
influenced by the positioning of the animal during anaesthesia.
Dorsal recumbancy with the head tilted down was the most vulnerable
position. In this position reflux occurred in 100% of cases as
compared with right lateral recumbancy with head up position where
the occurrence of reflux was only 12%.
Intraruminal pressure built up during anaesthesia was monitored
over a period of 60 minutes. Two planes of anaesthesia, light and
deep, were maintained for two 30 minute periods in a single anaesthetic session. Intraruminal pressure build up in deep followed
by light anaesthesia was significantly greater than that in light
followed by deep anaesthesia. The maximum pressure gradient between
the rumen and thoracic oesophagus and the occurrence of reflux were
recorded and it was found that only 24% of refluxes were associated
with the maximum pressure gradient. The intraruminal pressure
build up in the starved sheep was significantly lower when compared
with that of the unstarved sheep.
The effects of intraruminal insufflation on the occurrence of
reflux were investigated and it was found that the intraruminal pressure required to produce reflux was unusually high (about 40 mmHg) in
comparison with pressures that can be built up during normal periods
of anaesthesia lasting for 2-3 hours.
The influence of halothane anaesthesia on the motor functions
of the oesophagus and rumen was studied using manometric and electromyographic techniques in both light and deep planes of anaesthesia.
The motility of these organs was frequently present in light anaesthesia while it was almost totally abolished in deep anaesthesia.
The oesophageal pressure waves in light anaesthesia were always
peristaltic in nature, the velocity being 25 cm/sec.
A zone of high pressure was detected at the gastro-oesophageal
junction in the anaesthetized sheep using balloon tip catheter and
a pull through technique. The length of this zone was 2.9 cm.
The resting LOS pressure measured by balloon tip catheter was significantly greater than that measured by open tip catheter. The
resting LOS pressure was not significantly influenced by the depth
of anaesthesia. The LOS usually contracted prior to rumen contraction in light anaesthesia. In deep anaesthesia, when the oesophageal and ruminal contractions were totally abolished, the LOS
still showed rhythmic fluctuation in baseline pressure.
The response of LOS to an increase in intraruminal pressure
was studied. The LOS pressure was also increased with the increase
of intraruminal pressure. The occurrence of reflux was associated
with diminished LOS pressure.
The influence of pentagastrin, atropine sulphate and propranolol
hydrochloride on LOS pressure was studied. The LOS pressures were
increased within one minute of pentagastrin injection while after
atropine, the pressure was decreased within one minute. These
changes in LOS pressure however were not statistically significant.
Propranolol (after atropine) also had no significant influence on
LOS pressure.
The motor activities of the oesophagus, gastro-oesophageal
junction and reticulorumen were studied by electromyography (EMG).
These activities in the cervical oesophagus were characterised by
individual spikes in light anaesthesia which were almost abolished
in deep anaesthesia. The reticular and ruminal EMGs comprised of
regular spike bursts, the reticular bursts usually preceded the
ruminal ones. These activities were usually present in light anaesthesia while in deep anaesthesia they were totally abolished. The
electromyographic activity of the gastro-oesophageal junction was
characterised by continuous spike discharges which were present in
both light and deep planes of anaesthesia.
The influence of intravenous anaesthetic agents (pentobarbitone,
thiopentone, chloral hydrate-magnesium sulphate and alphaxalone/
alphadolone) on the intraruminal pressure build up, oesophageal and
ruminal motility and gastro-oesophageal reflux was studied. The
largest intraruminal pressure build up was found in alphaxalone/
alphadolone anaesthesia and the smallest with thiopentone anaesthesia.
The highest incidence of reflux was found with thiopentone (70%)
and the lowest with alphaxalone/alphadolone (40%) anaesthesia.
The barbiturates (pentobarbitone and thiopentone) caused total
abolition of oesophageal and ruminal motor functions in both light
and deep planes of anaesthesia. These activities, however, were
frequently present in light chloral hydrate and alphaxalone/alphadolone anaesthesia. The direction of the oesophageal pressure waves
in these studies was peristaltic.