Articles: anesthetics.
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The interactions of four anaesthetic drugs (ketamine, propanidid, Althesin and methohexitone) with two neuromuscular blocking agents (suxamethonium and pancuronium) have been investigated. On the isolated rat phrenic nerve-diaphragm preparation, all the anaesthetic drugs examined potentiated suxamethonium more than they potentiated pancuronium. ⋯ With the exception of Althesin, all the anaesthetics decreased the sensitivity of the frog rectus preparation to acetylcholine. The possible sites and mechanisms of these interactions are discussed.
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The effects of sodium thiopentone 19-757 mumol/litre, sodium pentobarbitone 25-806 mumol/litre, propanidid 74-1186 mumol/litre, Althesin 55-220 mumol/litre, diazepam 17.6-140 mumol/litre and ketamine 1.8-116.8 mumol/litre on the time-course of miniature end-plate currents of the excised mouse diaphragm were investigated. The currents were detected by means of extracellular electrodes and recorded with a transient recorder. ⋯ This reduction in the duration of end-plate currents reduced the amplitude of postsynaptic potentials. A similar effect at central synapses may account for a failure of synaptic transmission caused by anaesthetic drugs and it is suggested that a reduction in the lifetime of open postsynaptic ionic channels is a common action of anaesthetic drugs.
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Operating-room personnel exposed over a long period to trace concentrations of anesthetic gases may acquire both organic disturbances and impairment of cerebral function, though this has not been proven. However, the dangers of miscalculations due to disturbances of cerebral function and the fact that all working personnel should be breathing unpolluted air are sufficient indications to make scavenging of anesthetic gases mandatory. Scavenging has been carried out in many hospitals. At Vancouver General Hospital venting of the gases has decreased the nitrous oxide pollution to what is considered an acceptable level.
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The cardiocirculatory responses to equianaesthetic concentrations (MAC 0.5 and MAC 1.0 plus 67% N2O) of halothane, methoxyflurane, enflurane and isoflurane were studied in a total of 35 closed-chest dogs during ventilation controlled to produce normocapnia. Each anaesthetic produced a dose-related decrease in mean arterial pressure and in values reflecting cardiac function. These included cardiac output, stroke volume, left ventricular max dp/dt and ejection fraction. ⋯ Parallel with the depression in cardiac performance and blood pressure as two of the main predictors of energy demand, myocardial oxygen consumption was found to be significantly reduced by each of the anaesthetics. The ratio of the external work of the left ventricle to its oxygen consumption indicated that myocardial efficiency deterioated. The clinical implications are discussed.