Articles: anesthetics.
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In order to test the requirement of Na channel inactivation for the action of local anesthetics, we investigated the inhibitory effects of quaternary and tertiary amine anesthetics on normally inactivating and noninactivating Na currents in squid axons under voltage clamp. Either the enzymatic mixture pronase, or chloramine-T (CT), a noncleaving, oxidizing reagent, was used to abolish Na channel inactivation. We found that both the local anesthetics QX-314 and etidocaine, when perfused internally at 1 mM, elicited a "tonic" (resting) block of Na currents, a "time-dependent" block that increased during single depolarizations, and a "use-dependent" (phasic) block that accumulated as a result of repetitive depolarizations. ⋯ The voltage dependence of the steady state phasic block in CT-treated axons differed from that in the controls; an 8-10% reduction of the maximum phasic block and a steepening and shift of the voltage dependence in the hyperpolarizing direction resulted from CT treatment. The results show that these anesthetics can bind rapidly to open Na channels in a voltage-dependent manner, with no requirement for fast inactivation. We propose that the rapid phasic blocking reactions in nerve are consequences primarily of channel activation, mediated by binding of anesthetics to open channels, and that the voltage dependence of phasic block arises directly from that of channel activation.
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Comparative Study
Propofol or thiopentone: effects on intraocular pressure associated with induction of anaesthesia and tracheal intubation (facilitated with suxamethonium).
Changes in intraocular pressure (IOP) were studied in patients given propofol 2.1 mg kg-1 (n = 30) or thiopentone 4.9 mg kg-1 (n = 30) followed by suxamethonium 1.0 mg kg-1 and tracheal intubation. Half the patients in each group received an additional smaller dose of the same induction agent (propofol 1.0 mg kg-1 or thiopentone 2.0 mg kg-1) immediately before intubation. Both agents produced significant decreases in IOP which were slightly more marked with propofol. ⋯ Intubation of the trachea produced the greatest increase in IOP, averaging about 25% above control in all groups except in the group given the additional dose of propofol, in whom IOP remained below control values throughout the process of induction and intubation. Ten patients (33%) experienced pain on injection with propofol. A decrease in systolic arterial pressure of more than 30% was observed in 12 patients (40%) receiving propofol, compared with three (10%) of those given thiopentone.
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At present, the most widely used inhalational anaesthetics are the halogenated, inflammable vapours halothane, enflurane, isoflurane and the gas nitrous oxide. The anaesthetic effect of these agents is related to their tension or partial pressure in the brain, represented at equilibrium by the alveolar concentration. The minimum alveolar concentration for a specific agent is remarkably constant between individuals. ⋯ Sevoflurane is an experimental ether vapour: induction and recovery is fast and pleasant. It is metabolised to the same extent as enflurane and subnephrotoxic concentrations of inorganic fluoride may result. Sevoflurane has fewer respiratory and cardiovascular depressant effects than halothane and may be a future alternative for paediatric anaesthesia.(ABSTRACT TRUNCATED AT 400 WORDS)
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Comparative Study Clinical Trial Controlled Clinical Trial
The minimum alveolar concentration (MAC) of sevoflurane in humans.
Forty surgical patients were divided into two groups and anesthetized with either sevoflurane and oxygen or sevoflurane, oxygen, and nitrous oxide. The minimum alveolar concentration (MAC) for sevoflurane required to prevent movement in response to surgical incision in healthy patients was 1.71 +/- 0.07% (SE). ⋯ The reduction in sevoflurane MAC was 61.4%. The AD95 for sevoflurane with 63.5% end-tidal nitrous oxide was 0.94%.