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Studies on isoflurane anaesthesia in psittacine birds

Jaensch, Susan Mary (2001) Studies on isoflurane anaesthesia in psittacine birds. PhD thesis, Murdoch University.

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Abstract

The aim of the studies reported in this thesis was to describe the effects of isoflurane anaesthesia on the hepatic and respiratory systems in psittacine birds, as these are the two most commonly compromised organ systems during human anaesthesia. The results of these studies will lead to improved understanding of avian anatomy and physiology, and improvement of the current methodologies of anaesthesia administration.

Galactose and indocyanine green (ICG) clearances assays were compared with plasma and serum biochemical markers of liver dysfunction in normal chickens and galahs. following coeliotomy and following partial hepatectomy. Coeliotomy did not delay clearance of either compound, but partial hepatectomy resulted in elevation of galactose single point concentrations in chickens and decreased galactose clearance rates in galahs. Serum bile acids were not significantly elevated by either coeliotomy or partial hepatectomy. Alterations in plasma enzymes following coeliotomy and partial hepatectomy were consistent with muscle damage and not hepatic disease. Galactose single point concentrations and galactose clearance tests have the potential to be used both as sensitive, specific assays for screening for hepatic disease and for monitoring the progression of hepatic disease in birds. Isoflurane anaesthesia resulted in no detectable disturbance of hepatic function in either species.

The induction of pulmonary oxygen stress and oxygen toxicity was evaluated in budgerigars exposed to either acute, repeated acute or chronic periods of normobaric hyperoxic environments. Assays of a range of enzymic and non-enzymic antioxidants, blood gases and indicators of lipid membrane peroxidation were performed, and the lungs were evaluated by histology and transmission electron microscopy. All durations of oxygen exposure resulted in significant respiratory alkalosis and increased blood and plasma glutathione peroxidase activities. The concentrations of other pulmonary enzymic antioxidants including glutathione reductase and superoxide dismutase were not significantly altered by oxygen exposure. With increasing duration of exposure, the ratio of oxidised to reduced glutathione was significantly increased, while the concentrations of uric acid, a- and y-tocopherols and carotenoids were venous significantly reduced, especially following chronic exposure. Pulmonary concentrations of malonaldehyde and 4-hydroxyalkenal were not significantly increased, while plasma concentrations of 8-epi isoprostane F2ft were significantly elevated following oxygen exposure. Chronic oxygen exposure resulted in significant alteration of the respiratory exchange tissue, with increased parabronchial oedema, epithelial hyperplasia and inflammatory cell infiltration, and significant changes in cell morphology including thickening of endothelial cells, interstitial oedema and ruffling of respiratory epithelial cells.

These results indicate that budgerigars develop pulmonary oxygen stress following acute or repeated acute exposure to hyperoxic environments, progressing to pulmonary oxygen toxicity with chronic exposure. Assay of plasma 8-epi isoprostane F2α and blood non-enzymic antioxidants were the most sensitive methods of detecting oxygen stress and oxygen toxicity respectively.

The comparative respiratory functional anatomy of sulphur crested cockatoos and galahs studied by evaluation of a respiratory cast of a sulphur crested cockatoo, blood gas analysis, airsac gas-in-gas analysis and spirometry studies in anaesthetised birds. The respiratory functional anatomy of sulphur crested cockatoos was different to that previously described in non-psittacine species, with more extensive cranial and caudal thoracic airsacs and smaller abdominal airsacs. Blood gas analysis indicated significant was arterial and venous hyperoxia as a result of using 100% oxygen as the anaesthetic carrier gas. Ventilation of the clavicular airsac was significantly less than either the cranial or caudal thoracic airsacs.

Both endotracheal and caudal thoracic administration of anaesthetic gases provided reliable methods for maintaining anaesthesia and resulted in minimal alteration in respiratory function with the exception of arterial and venous hyperoxia. With both delivery methods, spontaneous respiratory movements and tidal and minute ventilation were not significantly decreased. In contrast, clavicular airsac administration of anaesthesia was not successful either in providing ventilation or maintaining anaesthesia due to lack of spontaneous ventilation of this airsac.

Item Type: Thesis (PhD)
Murdoch Affiliation: Division of Veterinary and Biomedical Sciences
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: repository@murdoch.edu.au. Thank you.
Supervisor(s): Raidal, Shane and Cullen, Len
URI: http://researchrepository.murdoch.edu.au/id/eprint/53177
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