L.K. Cullen

Medetomidine sedation in dogs and cats: A review of its pharmacology, antagonism and dose

Medetomidine is a relatively new sedative analgesic in dogs and cats but some precautions are required when using it. It is a potent alpha 2-adrenoceptor agonist and stimulates receptors centrally to produce dose-dependent sedation and analgesia and receptors centrally and peripherally to cause marked bradycardia and decrease the cardiac output. While hypotension occurs frequently, higher doses of the sedative can raise the blood pressure due to an affect on peripheral receptors. Slowing of the respiratory rate is a frequent effect of medetomidine with some dogs showing signs of cyanosis. Other actions that follow medetomidine use are slowing of gastrointestinal motility, hypothermia, changes to endocrine function and, occasionally, vomiting and muscle twitching. The clinical use of medetomidine in dogs and cats is discussed. Recommended dose rates are presented along with precautions that should be taken when it is used alone for sedation, as an anaesthetic premedicant or in combination with ketamine, propofol or opioids. Hypoxaemia occurs frequently in dogs given medetomidine and propofol. The actions of medetomidine can be rapidly reversed with the specific alpha 2-adrenoceptor antagonist, atipamezole, which is an advantage because undesirable and sedative actions of medetomidine can be terminated.

Comparison of Endotracheal, Caudal Thoracic Air Sac, and Clavicular Air Sac Administration of Isoflurane in Sulphur-Crested Cockatoos (Cacatua galerita)

Abstract Ten sulphur-crested cockatoos (Cacatua galerita) were anesthetized twice, 2 weeks apart, to evaluate the effects on respiratory function of endotracheal (ET), caudal thoracic (CT) air sac, and clavicular air sac administration of isoflurane anesthesia. Four administration methods were evaluated by administering anesthetic gases through either the ET tube or the air sac as an open or closed system. Respiratory function was monitored by arterial and venous blood gas determination, gas-in-gas determination of both ET tube and air sac gases, and spirometry. Both ET tube and CT air sac administration provided a reliable method of maintaining anesthesia and resulted in minimal alteration in respiratory function. Blood pH, partial pressure of carbon dioxide (Pco2), bicarbonate, total carbon dioxide, and base excess were not significantly altered by CT air sac administration. Increased partial pressure of oxygen and oxygen saturation were evidence of hyperoxia. CT air sac Pco2 decreased to 12.7 ± 7.9 mm Hg with CT administration, and this was sufficient to maintain spontaneous respiratory movements. Spirometry demonstrated maintenance of tidal and minute volumes with each administration method despite apparent reduction in visible respiratory movements. Clavicular air sac administration was not successful in providing ventilation or maintaining anesthesia. Despite the demonstrated ability to flush a bolus of gas through this air sac and out the ET tube, no spontaneous ventilation was detected in this air sac in either an open or closed system, preventing delivery of sufficient isoflurane to maintain anesthesia.

Assessment of Liver Function in Galahs (Eolophus roseicapillus) After Partial Hepatectomy: A Comparison of Plasma Enzyme Concentrations, Serum Bile Acid Levels, and Galactose Clearance Tests

Abstract The relative sensitivity of conventional assays of liver function was evaluated in comparison with galactose clearance, a test of liver function used in humans since the 1960s. Results of galactose clearance tests were compared with plasma enzyme concentrations and serum bile acid levels in clinically normal galahs (Eolophus roseicapillus; n = 8), after celiotomy (n = 4), and after 6% or 18% hepatectomy (n = 8, respectively). Clearance tests and biochemical analyses were performed within 2–4 hours of surgery and at 4 and 7 days after surgery. Celiotomy and 6% and 18% hepatectomy resulted in changes in alkaline phosphatase, aspartate aminotransferase, and alanine aminotransferase concentrations that were consistent with muscle trauma. Celiotomy and 6% hepatectomy did not significantly alter the results of galactose clearance tests; however, 18% hepatectomy resulted in significant reduction in galactose clearance and galactose clearance as a function of body surface area (GEC-SA). Galactose single-point concentrations were not significantly elevated at any time during the experiments; however, single-point concentrations were strongly correlated with galactose clearance and GEC-SA values, especially at 80 minutes after galactose injection. Serum bile acid levels were not significantly elevated after celiotomy or partial hepatectomy. Measurement of galactose single-point concentrations has the potential to be a simple, sensitive method of screening for reduced hepatic function in birds. Galactose clearance and GEC-SA have the potential to be sensitive assays of hepatic functional mass, for use as a noninvasive method of monitoring hepatic function.

Biochemical and haematological changes following prolonged halothane anaesthesia in horses.

Six healthy horses were anaesthetised with halothane (1.2 times the horse minimal alveolar concentration) in oxygen for more than 12 hours. Serum bilirubin, aspartate aminotransferase, alkaline phosphatase and L-iditol dehydrogenase values were significantly (P < 0.05) increased for up to nine days after anaesthesia. These changes suggest an anaesthesia related liver dysfunction. Creatine kinase increased to an average of more than 1400 IU litre-1 24 hours after anaesthesia and this change is indicative of muscle cell disruption. Renal-associated biochemical results, (that is serum creatinine and inorganic phosphate concentrations) were significantly increased transiently and are indicative of reduced renal function during and immediately after anaesthesia. Plasma concentrations of eicosanoids (6-keto-PGF1a, PGF2a, PGE and thromboxane) following anaesthesia were not different from preanaesthetic values. The magnitude of liver and muscle cell related increases in serum enzyme activities resulting from prolonged halothane anaesthesia was in excess of that previously reported for anaesthesia of shorter duration.

EFFECTS OF TILETAMINE/ZOLAZEPAM PREMEDICATION ON PROPOFOL ANAESTHESIA IN DOGS

The cardiovascular and pulmonary effects of tiletamine/ zolazepam, propofol and tiletamine/zolazepam plus propofol were studied in five mongrel dogs. A cannula inserted into a raised carotid artery was used to measure mean arterial pressure (MAP) and heart rate continuously and to collect arterial blood for the determination of pH, PO2, PCO2, bicarbonate and base balance. Respiratory frequency and rectal temperature were also recorded. In the two propofol groups premedication had no significant effect on the time to rejection of an endotracheal tube and the return to sternal recumbency. The MAP and heart rate increased after tiletamine/zolazepam alone and after tiletamine/zolazepam plus propofol, although propofol alone reduced MAP and transiently increased heart rate. Respiratory frequency decreased transiently in both propofol groups in association with a significant increase in PaCO2 and decrease in PaO2. The most notable change was the hypoxaemia in the tiletamine/zolazepam plus propofol group in which the PaO2 was reduced. In all the dogs given tiletamine/ zolazepam alone undesirable side effects were observed, effects which also occurred during the recovery of the dogs given tiletamine/zolazepam plus propofol.

Normobaric hyperoxic stress in budgerigars: non-enzymic antioxidants

The effects of oxygen exposure on pulmonary and blood non-enzymic antioxidant concentrations was evaluated in budgerigars (Melopsittacus undulatus). Budgerigars were exposed to acute (3 h), repeated acute (3 exposures each of 3 h) or chronic (72 h) normobaric hyperoxic environments and the pulmonary and plasma concentrations of selected non-enzymic antioxidants, namely glutathione, uric acid, alpha- and gamma-tocopherol and carotenoids were assayed. With increasing duration of oxygen exposure, the ratio of oxidised to reduced glutathione was significantly increased, while the concentrations of uric acid, alpha- and gamma-tocopherol and carotenoids were significantly reduced, especially following chronic oxygen exposure. Following acute and repeated acute exposure, alteration in glutathione concentrations and reduction in alpha-tocopherol concentrations indicated oxygen stress. Following chronic exposure, depletion of non-enzymic antioxidants indicated exhaustion of these protective mechanisms and progression from oxygen stress to oxygen toxicity.

Comparison of femoral and auricular arterial blood pressure monitoring in pigs

OBJECTIVE To compare arterial blood pressure measurements obtained from the femoral and auricular arteries in anaesthetized pigs. STUDY DESIGN Prospective experimental study. ANIMALS Fifteen female Large White pigs were used weighing 21.3 +/- 2.3 kg. METHODS The pigs were anaesthetized with tiletamine/zolazepam and xylazine administered intramuscularly, and anaesthesia maintained with isoflurane delivered in oxygen/nitrogen. Arterial oxygen partial pressures were maintained between 11.3 and 13.3 kPa and PaCO(2) between 4.6 and 6.0 kPa. Monitoring included electrocardiogram, capnography and invasive blood pressure. The auricular and femoral arteries were catheterized for continuous systolic (SAP), diastolic (DAP) and mean arterial pressure (MAP) measurements. Measurements were recorded every 15 minutes. Statistical analysis involved a Bland-Altman plot analysis. RESULTS The mean difference +/- confidence intervals between the femoral and the auricular arterial diastolic, systolic and mean blood pressure measurements during hypotension were 2 +/- 7, 2 +/- 5 and 2 +/- 5 mmHg respectively. In conditions of normotension mean difference +/- confidence intervals, of femoral and auricular arterial blood pressure measurements of diastolic, systolic and mean blood pressure were 4 +/- 5, 3 +/- 7 and 4 +/- 4 mmHg respectively. In conditions of increased arterial blood pressure, mean difference +/- confidence intervals, of femoral and auricular arterial blood pressure measurements of diastolic, systolic and mean blood pressure were 4 +/- 5, 3 +/- 8 and 4 +/- 4 mmHg respectively. CONCLUSION Auricular artery catheterization is easier and quicker to perform. Pressure measurements from the auricular artery compared well with the femoral artery. CLINICAL RELEVANCE We found that auricular arterial blood pressures were similar to femoral arterial values under the conditions of this experiment. We did not test extremes of blood pressure or significant alterations in body temperature.

Assessment of liver function in chickens using galactose and indocyanine green clearances

Values for galactose and indocyanine green (ICG) clearances, and plasma and serum biochemical markers of liver dysfunction were determined in normal chickens and following coeliotomy, and compared with birds after partial hepatectomy. Clearance tests, and serum and plasma biochemistry were performed 4h, and 4 and 7 days after surgery. Coeliotomy and manipulation of the liver did not delay clearance of either compound. Partial hepatectomy resulted in elevation of galactose single point concentrations but did not significantly alter galactose clearance (GEC) values. Clearance values of ICG were not significantly altered. Biochemical values were not significantly elevated in birds after a partial hepatectomy in comparison with birds after coeliotomy. Galactose single point concentrations have the potential to become a simple, relatively non-invasive method of screening for liver disease, with GEC tests having the potential to quantify the degree of loss of functional hepatic mass.

Normobaric hyperoxic stress in budgerigars: enzymic antioxidants and lipid peroxidation.

The effects of acute (3 h), repeated acute (3 exposures each of 3 h) and chronic (72 h) normobaric hyperoxic exposure in budgerigars (Melopsittacus undulatus) were evaluated by monitoring the effects on pulmonary enzymic antioxidants, and indicators of lipid peroxidation. All durations of oxygen exposure resulted in significant respiratory alkalosis and elevated pulmonary and blood glutathione peroxidase concentrations. The concentrations of other pulmonary enzymic antioxidants including glutathione reductase and superoxide dismutase were not significantly altered by oxygen exposure. Pulmonary concentrations of the lipid peroxidation markers malonaldehyde and 4-hydroxyalkenal were not significantly elevated following oxygen exposure. Plasma concentrations of 8-epi isoprostane F(2alpha) were significantly elevated following both acute and repeated acute exposure. The results indicate that in budgerigars, both acute and chronic oxygen exposure can result in significant alteration in respiratory function and increased production of reactive oxygen species.

The pathology of normobaric oxygen toxicity in budgerigars (Melopsittacus undulatus)

The effects of normobaric oxygen exposure were investigated in budgerigars (Melopsittacus undulatus). Sixty birds were randomly divided into four equal groups of 15. These groups were randomly allocated as control, acute exposure, repeated acute exposure or chronic exposure. Control birds were exposed to 72 continuous hours of 21% oxygen in a sealed, enclosed chamber. Acute exposure, repeated acute exposure and chronic exposure groups were exposed oxygen at minimum concentration of 95% for a single 3-h period, a 3-h period daily for three sequential days, or a single 72-h period in a sealed, enclosed chamber, respectively. Oxygen exposure resulted in significant alteration in the histological morphology of respiratory exchange tissue, with severe oedema, and inflammatory cell infiltration. Electron micrographs revealed thickening of the blood-gas barrier with the tissue harmonic thickness increasing from 226 - 90 nm in control birds to 639 - 393nm following repeated acute exposure, with the total harmonic thickness increasing from a control value of 345 - 146nm to 837 - 423 nm at the same time. Chronic oxygen exposure resulted in significant changes in cell morphology including thickening of endothelial cells, ruffling of type I respiratory endothelial cells and interstitial vacuolation. These results indicate that budgerigars undergo significant morphological and ultrastructural changes in respiratory exchange tissue following exposure to 100% oxygen.