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Mette, Astrid (2008): Untersuchungen zur Isofluran-Narkose beim Schwein. Dissertation, LMU München: Faculty of Veterinary Medicine
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Abstract

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.