Laboratory animals
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The effects of a rapid increase in inspired desflurane concentration on systemic haemodynamics and plasma catecholamines were studied in seven pigs (22-30 kg). Following premedication (flunitrazepam 0.4 mg/kg i.m.), anaesthesia was induced (propofol 2.5 mg/kg i.v., vecuronium 0.2 mg/kg i.v.), the trachea orally intubated, and ventilation controlled. Anaesthesia was maintained with N2O/O2 (70%/30%), propofol (50 micrograms/kg/min), desflurane (2% end-tidal concentration), and vecuronium (0.3 mg/kg/h). ⋯ There was an immediate decrease in MAP. Plasma levels of E and NE remained unchanged throughout. In conclusion, in contrast to findings in humans, a rapid increase in inspired desflurane concentration does not cause a hyperdynamic circulatory response in the pig.
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Comparative Study
Effects of isoflurane versus halothane on myocardial contractility in rabbits: assessment with transthoracic two-dimensional echocardiography.
The effects of isoflurane versus halothane on cardiac contractility were evaluated by two-dimensional (2D) transthoracic echocardiography in rabbits. The relationship between the left ventricular end-systolic wall stress (LVESWS) and the velocity of heart rate corrected circumferential fibre shortening (Vcfc) was used. Arterial blood pressure, heart rate, left ventricular pressure and transthoracic 2D echocardiogrphic data were determined at 1 MAC (minimum alveolar concentration) of halothane or isoflurane, both with 50% nitrous oxide. ⋯ Myocardial contractility under isoflurane/nitrous oxide anaesthesia was significantly higher than under halothane/nitrous oxide anaesthesia at 1 MAC. The results of the present study confirm data obtained from humans and other animal species and suggest that, in rabbits, myocardial contractility is best preserved by inhalation of isoflurane. Isoflurane should therefore be preferred over halothane, especially in cases of prolonged anaesthetic procedures.
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Endotracheal intubation allows precise delivery of inhaled anaesthetic agents. Intubation in small non-human primates (less than 1 kg), is straightforward, using commercially available equipment, and careful positioning of the animal. Equipment and methods are fully described and illustrated.
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Endotracheal intubation of rabbits is reported, both personally and in the literature, to be so difficult that special equipment has been constructed by other workers to facilitate the procedure. We report that the positioning of the operator, behind the animal, viewing from the dorsal surface of the head, facilitates this procedure enormously.
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Heart rate, arterial blood pressure and blood acid-base status were determined in 18 adult female mink (mean (+/- SEM) body weight 1052 +/- 34 g) during long-term anaesthesia with either controlled ventilation (n=12) or spontaneous respiration (n=6). Surgical anaesthesia was induced by intramuscular injection of ketamine hydrochloride (Ketaminol Vet, 40.0 +/- 1.7 mg/kg) and midazolam hydrochloride (Dormicum 2.8 +/- 0.1 mg/kg) and maintained for at least 5 h by continuous intravenous infusion of this drug combination in 0.9% saline. For all animals, the mean rates of infusion of ketamine and midazolam were 48.4 +/- 1.6 and 1.61 +/- 0.12 mg/h, respectively. ⋯ It is concluded that the procedure described for long-term anaesthesia in mink is convenient and safe for acute physiological experiments in this species, provided normal body temperature and pulmonary gas exchange is sufficiently maintained. Thus, the need for an adequately controlled artificial ventilation is strongly emphasized. Finally, a proposal for the composition of an intravenous solution, containing ketamine and midazolam hydrochloride, and sodium bicarbonate in saline, suitable for long-term anaesthesia in adult mink is presented.