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A Journal on Anesthesiology, Resuscitation, Analgesia and Intensive Care

Official Journal of the Italian Society of Anesthesiology, Analgesia, Resuscitation and Intensive Care
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Minerva Anestesiologica 1999 July-August;65(7-8):555-9

language: English

Electric ­nerve stim­u­la­tion: anal­y­sis of two clin­i­cal cas­es of ­failed ­nerve elec­tro­lo­ca­tion by ­using ­sheathed nee­dles

Di Massa A. 1, Cappelletti R. 2, Carriero D. 1, Pede O. 1, Cozzolino A. 3

1 Università ­degli Studi - Siena, Cattedra di Terapia del Dolore;
2 ASL n. 1 - Napoli, Ospedale «Dei Pellegrini» , Servizio di Anestesia e Rianimazione;
3 Università ­degli Studi - Siena, Cattedra di Chirurgia Maxillo-Facciale


The aim of this work was to ­explain the rea­sons of two unsuc­cess­ful ­blocks of sciat­ic ­nerve ­even if anaesthet­ic solu­tion was inject­ed ­through insu­lat­ed nee­dle on elic­it­ed ­twitch. The clinical cases were two out­pa­tients under­go­ing diag­nos­tic arthros­co­py of ­knee ­under anaesthet­ic ­block of sciat­ic and femo­ral ­nerves. In ­both ­patients, the mus­cu­lar ­twitch ­appeared ­when the ischi­atic ­bone was ­kept in unex­pect­ed ­touch ­with nee­dle tip. In ­spite of the ­attempt to ­locate cor­rect­ly the nee­dle (the ­touch ­with ­bone ­means ­that the ­nerve is not in ­front of the nee­dle tip), the injec­tion of anaesthet­ic solu­tion was unsuc­cess­ful. In clin­i­cal envi­ron­ment, when elec­tro­in­su­lat­ed nee­dles gath­ered ­total ­amount of admin­is­tered cur­rent on the nee­dle tip, it was not pos­sible to elic­it a ­twitch ­just at the moment of ­touch of the nee­dle ­with ­the bone. Referred ­events dis­agree ­with ­some experi­men­tal ­works per­formed out of clin­i­cal envi­ron­ment, which found­ ­that ­total ­amount of admin­is­tered cur­rent ­through an insu­lat­ed nee­dle gath­ers ­always in ­front of the tip. Our clin­i­cal obser­va­tions ­seems to con­firm an elec­tro­lo­ca­tion mis­take ­called “electri­cal shad­ow”. The abil­ity of ­sheathed nee­dles to ­work as occa­sion­al capac­i­tor due to the alter­nation of two con­duc­tor ­layers (nee­dle ­shaft and tis­sue) and of a die­lec­tric (coat­ing mate­ri­al) can ­explain ­some miss­ing elec­tro­lo­ca­tions, as the appear­ance of ­electric ­fields with­in die­lec­tric nee­dle sheath­ing.

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