[Electric nerve stimulation in relation to impulse strength. A quantitative study of the distance of the electrode point to the nerve].

In the present study the difference of the distances of the tip of the needle to the nerve at similar current intensities but different pulse widths (100 microseconds vs. 1000 microseconds) were determined by means of 20 blockades of the sciatic nerve using the transgluteal approach of Labat. Comparable current intensities at different pulse widths (100 microseconds vs. 1000 microseconds) were compared in the same way, using the same position of the needle. At a pulse width of 100 microseconds and a current intensity of 0.30 mA, the tip of the needle is on an average of 5.0 mm closer to the nerve than with a pulse width of 1000 microseconds and a comparable current intensity of 0.28 mA (difference statistically highly significant; p < 0.005). The comparison of the current intensities at different pulse widths at the same needle-position shows that the difference of the current intensities becomes lower when approaching the nerve. At the most distant point measured in this study, a current intensity of 0.94 mA at 100 microseconds corresponds to an aquivalent current of 0.30 mA at 1000 microseconds (difference 0.64 mA); after an approach of 5.0 mm to the sciatic nerve, this difference is significantly lower (0.30 mA at 100 microseconds, 0.11 mA at 1000 microseconds, difference 0.18 mA; p < 0.01). This means that the control of peripheral nerve stimulation is superior at a pulse width of 100 microseconds because a similar distance corresponds to a greater difference of the current. The success rate of the blockade was 95% at a current of 0.30 mA at 100 microseconds. Nerve lesions or other complications have not been seen. In conclusion, safe and successful nerve blocks in patients without polyneuropathia using the peripheral nerve stimulation seems to be obtained at a current intensity of about 0.30 mA at a pulse width of 100 microseconds.