British journal of anaesthesia
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The effect of Althesin, diazepam, ketamine, propanidid and thiopentone on the release of acetylcholine was tested at the mouse neuromuscular junction. Althesin, diazepam and thiopentone increased the quantal content of the end-plate potential. Ketamine at low concentration (3.6 micromol litre-1) had a similar effect, but at high concentration (116.7 micromol litre-1) quantal content decreased sharply. ⋯ The increase in quantal content antagonized the effect of postsynaptic depression on the amplitude of the end-plate potential. The lack of enhancement of acetylcholine release appears to explain the in vitro interaction of propanidid with tubocurarine. The diversity of presynaptic actions of these drugs makes it unlikely that this is an important mechanism in producing anaesthesia.
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A study of controlled hypotension was undertaken in 50 major surgical patients using labetalol, a drug with both alpha- and beta-adrenoceptor blocking activity. The patients were such that difficulty in achieving controlled hypotension could be anticipated: the young, the anxious and those for whom halothane was contraindicated. The administration of labetalol quickly induced hypotension which was controlled easily and was rapidly antagonized.
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We have evaluated a new method for measuring the oxygenated mixed venous PCO2 (PVCO2) in patients undergoing general anaesthesia. The lungs were inflated with a gas mixture containing 0% carbon dioxide and then 12% carbon dioxide and the expired gas was analysed both before and after a brief period of breath-holding. PVCO2 was estimated from the differences in carbon dioxide concentration before and after the apnoeic period. ⋯ The range of PaCO2 studied was 3.2--6.13 kPa. The relationship between mixed venous and arterial PCO2 was found to be PaCO2 = 0.87 PVCO2--0.44 (r = 0.91). We conclude that this method for measuring PVCO2 can be used during anaesthesia allowing PaCO2 to be estimated with considerable accuracy.