Transient impairment of the axolemma following regional anaesthesia by lidocaine in humans. (13th May 2014)

• Record Type: Journal Article
• Authors: Moldovan, Mihai; Lange, Kai Henrik Wiborg; Aachmann‐Andersen, Niels Jacob; Kjær, Troels Wesenberg; Olsen, Niels Vidiendal; Krarup, Christian
• Is Part Of: Journal of physiology. Volume 592:Number 13(2014:Jul.)
• Page Start: 2735
• Page End: 2750
• Publication Date: 2014-05-13
• Subjects: Physiology -- Periodicals; 612.005
• DOI: 10.1113/jphysiol.2014.270827
• Languages: English
• ISSNs: 0022-3751

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <sec id="tjp6173-sec-0010" sec-type="section"> <title>Key points</title> <p> <list id="tjp6173-list-0001" list-type="bullet"> <list-item> <p>We tested the recovery of motor axon conduction and multiple measures of excitability by 'threshold‐tracking' after ultrasound‐guided distal median nerve regional anaesthesia by lidocaine.</p> </list-item> <list-item> <p>Lidocaine caused a transient conduction failure that recovered completely by 3 h, whereas excitability recovered only partially by 6 h and fully by 24 h.</p> </list-item> <list-item> <p>The up to 7‐fold increase in threshold after complete recovery of conduction was associated with excitability changes that could only partially be explained by block of the voltage‐gated Na<sup>+</sup> channel (VGSC).</p> </list-item> <list-item> <p>Mathematical modelling indicated that, apart from a reduction in the number of functioning VGSCs, lidocaine also caused a decrease of passive membrane resistance and an increase of capacitance.</p> </list-item> <list-item> <p>Our data suggest that lidocaine, even at clinical 'sub‐blocking' concentrations, could cause a reversible structural impairment of the axolemma.</p> </list-item> </list> </p> </sec> <sec id="tjp6173-sec-0020" sec-type="section"> <title>Abstract</title> <p>The local anaesthetic lidocaine is known to block voltage‐gated Na<sup>+</sup> channels (VGSCs), although at high concentration it was also reported to block other ion channel currents as well as to alter lipid membranes. The aim of this study was to investigate whether the clinical regional anaesthetic action of lidocaine could be accounted for solely by the block of VGSCs or whether other mechanisms are also relevant. We tested the recovery of motor axon conduction and multiple measures of excitability by 'threshold‐tracking' after ultrasound‐guided distal median nerve regional anaesthesia in 13 healthy volunteers. Lidocaine caused rapid complete motor axon conduction block localized at the wrist. Within 3 h, the force of the abductor pollicis brevis muscle and median motor nerve conduction studies returned to normal. In contrast, the excitability of the motor axons at the wrist remained markedly impaired as indicated by a 7‐fold shift of the stimulus–response curves to higher currents with partial recovery by 6 h and full recovery by 24 h. The strength–duration properties were abnormal with markedly increased rheobase and reduced strength–duration time constant. The changes in threshold during electrotonus, especially during depolarization, were markedly reduced. The recovery cycle showed increased refractoriness and reduced superexcitability. The excitability changes were only partly similar to those previously observed after poisoning with the VGSC blocker tetrodotoxin. Assuming an unaltered ion‐channel gating, modelling indicated that, apart from up to a 4‐fold reduction in the number of functioning VGSCs, lidocaine also caused a decrease of passive membrane resistance and an increase of capacitance. Our data suggest that the lidocaine effects, even at clinical 'sub‐blocking' concentrations, could reflect, at least in part, a reversible structural impairment of the axolemma.</p> </sec> </abstract>