Articles: nerve-block.
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The in vitro sensitivities to local anaesthetic blockade of A, B and C nerve fibres in rabbit vagus nerves were examined using a series of structurally similar amino-ester agents which varied in lipid solubility and anaesthetic potency. A fibres were found to be the most sensitive and C fibres the least sensitive to conduction blockade with all the agents, provided that equilibrium blockade was allowed to develop. A correlation existed between the intrinsic anaesthetic potency of the various agents and their lipid solubilities. ⋯ As lipid solubility decreased through the series studied, so the onset of conduction blockade of A fibres was prolonged. It is suggested that this related to decreasing ability to penetrate the lipid diffusion barriers around A fibres. The traditional view that C fibres were more sensitive to block may have arisen because of confusion between absolute sensitivity and rate of development of conduction blockade.
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Acta Anaesthesiol Scand · May 1985
Effects of adjuvants to local anaesthetics on their duration. I. Studies of dextrans of widely varying molecular weight and adrenaline in rat infraorbital nerve block.
Local anaesthetics of the amide type were studied in a modified rat infraorbital nerve block model, with which it was possible to determine varying degrees of sensory block. Of the agents investigated, 0.5% bupivacaine tended to give a longer duration of block than 2% prilocaine or 2% lidocaine, while 0.5% etidocaine had the shortest duration. The duration of prilocaine was prolonged by addition of adrenaline, 5 micrograms/ml, more than that of the other agents. ⋯ The extent of prolongation was dependent on the degree of block, the concentration of dextrans in the local anaesthetic solution, and the Mw of the dextran although in a less uniform way. An increase in the relative viscosity of the solutions might be a factor of importance for the prolonging effect of addition of dextran to local anaesthetics. Since a formulation providing analgesia of a long duration would be of clinical value, further studies on combinations of the comparatively low-toxicity agent prilocaine and macromolecular substances are of interest.