• R Fuzier, A-S Richez, O Choquet, and F Singelyn.
• Pôle d'anesthésie-réanimation, service d'orthopédie et traumatologie, CHU Purpan, université de Toulouse, place du Dr-Baylac, TSA 40031, 31059 Toulouse cedex 9, France. fuzier.r@chu-toulouse.fr
• Ann Fr Anesth Reanim. 2008 Oct 1;27(10):802-7.

ObjectiveWhen performing a peripheral nerve block, the current allowing local anaesthetic injection is between 0.3 and 0.5 mA. It has never been assessed if such a threshold remains the same whatever be the pulse duration. The aim of this study was to determine the minimal current required to stimulate a nerve while different pulse durations were applied, and to evaluate the importance of the placement of the cutaneous electrode.Study DesignProspective study.Patients And MethodsOne hundred and twenty posterior popliteal sciatic (S), femoral (F), or median (M) nerve blocks performed with a nerve stimulator were included. The minimal current for a clearly visible motor response of the corresponding muscle was recorded with a pulse duration set at 50, 150 and 300 micros. The same procedure was repeated with the electrode sited on the controlateral side, before injection of local anaesthetic.ResultsThe mean lowest charge of current required to stimulate a nerve was 24+/-8 nC at 50 micros. At 150 and 300 micros, it has to be increased by 175 % (42+/-14 nC) and 280 % (67+/-23 nC), respectively. No significant difference in the charge required was noted either among S, F, or M, or by changing the cutaneous electrode position. Adequate anaesthesia was noted in all cases.ConclusionThe relationship between intensity and pulse duration is not linear. Moreover, a low charge of current does not seem to be appropriate with pulse duration equal or superior to 300 micros. The location of the cutaneous electrode does not seem to be important.

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