Objective: We compared a few variables such as the type of needle, the direction of bevel, and the effect of stimulation duration in percutaneous peripheral nerve blockade. We also studied the real distribution of injected drug through nerve biopsy.

Method: The sciatic nerve-tibialis posterior muscle preparation of rabbit was chosen as a model. Experimental rabbits were divided into 3 groups: Group 1 (16 legs), use of insulated needle and 100μs stimulation duration; Group 2 (9 legs), use of insulated needle and 240μs stimulation duration; Group 3 (6 legs), use of uninsulated needle and 100μs stimulation duration. The mixed solution, 0.1 cc, of 5% phenol and indian ink was injected in 10 legs and the muscles were obtained to observe the spreads of injected solution after 2 weeks.

Results: The minimal stimulation currents of group 1, 2, 3 were 0.49 mA, 0.37 mA, 2.07 mA, respectively. The distance between needle and sciatic nerve sheath of group 1, 2, 3 were 0.09 mm, 0.11 mm, 0.20 mm in width, and 1.84 mm, 3.33 mm, 4.50 mm in depth, respectively. The current required to stimulate the nerve increased rapidly as the tip of the insulated needle passed the nerve, and the direction of bevel had no effect on the minimal stimulation current. Injected indian ink was located alongside the perineurium.

Conclusion: In three methods, the most exact method was the use of insulated needle and 100s stimulation duration. The needle tip was located 1.84 mm past the nerve.

Keywords :Electrical nerve localization, Nerve block