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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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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Randomized Controlled Trial Comparative Study Clinical Trial
Anaesthesia for evacuation of retained products of conception. Comparison between alfentanil plus etomidate and fentanyl plus thiopentone.
Forty-four patients presenting for evacuation of retained products of conception were anaesthetized with either fentanyl and thiopentone, or alfentanil with etomidate, along with 70% nitrous oxide in oxygen. There was no difference between the two techniques in indices of immediate recovery (time to opening eyes and obeying a simple command), but the rate of return of higher mental functions (assessed by a coin counting test) was significantly better using the alfentanil-etomidate technique. There was no statistically significant difference between the techniques for apnoea or abnormal movements during anaesthesia, but alfentanil with etomidate was associated with significantly more pain on injection and a higher frequency of postoperative vomiting (40%).