Investigations about the isoflurane anaesthesia in swine Compared
to other animal species, swine show typical defensive behaviour
towards any kind of physical manipulation. Anaesthesia is thus not
only indicated for surgical interventions but for diagnostic and
therapeutic measures as well. This study evaluates whether
inhalational anaesthesia with isoflurane via facemask can serve as
a potential alternative to regular intramuscular or intravenous
anaesthesia. Two different apparati are compared: the first one
disperses medical oxygen (O2), the second filtered compartment air
(CA), both in conjunction with isoflurane. Animals with a body
weight (BW) up to 20 kg receive simply an inhalational anaesthesia,
patients weighing more than 20 kg in addition to that an
intramuscular pre-medication 10 minutes earlier with ketamine (10
mg/kg BW) and azaperone (2 mg/kg BW). The survey examines 156
normal pigs and 19 statistically non-evaluated miniature pigs.
Animals with more than 10 kg BW in particular show vehement
physical reactions to the basal anaesthesia. Pre-medicated test
animals are immobilized after ten minutes and the anaesthesia can
be deepened with isoflurane. Animals receiving pure inhalational
anaesthesia show ataxia after 29 to 34 seconds. After 48 to 60
seconds the probands are in prone position and after 65 to 89
seconds in lateral position. The pre-medicated animals on the other
hand are significantly slower to show ataxia (after 1,4 minutes),
prone position (after 1,8 to 1,9 minutes) and lateral position (4,3
to 4,4 minutes). The hypnosis and surgical tolerance stage of
anaesthesia are reached significantly faster with isoflurane in CA
than with isoflurane in O2. Test animals with isoflurane/O2 require
an isoflurane-vaporiser position of 2,24 to 3,38 Vol% during the
whole intervention, those with isoflurane/CA 2,17 to 2,88 Vol%.
Compared to that, the premedicated animals need significantly less
isoflurane with 1,5 to 2,38 Vol% (O2) and 1,52 to 2,08 Vol% (CA).
Probands with O2 as carrier gas show a significantly better oxygen
saturation (94-95%) than test subjects with CA (78%). The measured
arterial pH value of 7,27 to 7,34 indicates a low acidosis; a
partial pressure of carbon dioxide of 49,7 to 65,7 mmHg exceeds the
reference values. The partial oxygen pressure is significantly
better with O2 (190,0 to 266,2 mmHg) than with CA (57,4 to 65,7
mmHg). During the recovery phase, all animals exhibit the
reappearance of the claw reflex, the dewclaw reflex, the muscle
tension and positive skin sensibility in consecutive order.
Somewhat later they raise their heads, get into the prone position
and try to rise. Given several more minutes, they manage to stand.
Probands receiving pure inhalation anaesthesia are significantly
faster (1,3 to 9,8 minutes) to reach the waking stage than animals
with a combination of ketamine, azaperone and isoflurane (2,1 to
24,4 minutes). The average blood pressure during the basal narcosis
is 128/71 mmHg (systole/diastole) and 130/72 mmHg during the
maintenance stage. Body weight and premedication apparently play no
significant role. Miniature pigs deliver similar results as the
premedicated pigs, but need remarkably less isoflurane (1,10 to
1,58 Vol%). Conclusion: a pure inhalation anaesthesia with
isoflurane in swine can only be recommended for animals with a body
weight up to 10 kg (O2-apparatus: 2,24 to 3,38 Vol% for surgical
tolerance, CA-apparatus: 2,17 to 2,88 Vol% for surgical tolerance);
rapid drifting off and rapid waking are the obvious advantages. A
premedication with ketamine (10 mg/kg BW) and azaperone (2mg/kg BW)
reduces the dose of isoflurane significantly (O2-apparatus: 1,5 to
2,38 Vol%, CA-apparatus: 1,52 to 2,08 Vol%). The use of O2 as
carrier gas allows an optimal anaesthesia with optimal O2 -
saturation for every animal weight and size (94 to 95%). CA as
carrier gas can cause hypoxia and acidosis (O2-saturation: 78%, pH:
7,31 to 7,33, pCO2: 53,0 to 60,4 mmHg, pO2: 57,4 to 65,7 mmHg)
during longer interventions. Miniature pigs need considerably less
isoflurane, though this cannot result solely from the
pre-medication and needs to be examined further.
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