Effects of perineural tramadol on nerve conduction of sural nerve

Objectives: The aim of this study was to investigate whether tramadol had a dose-dependent blocking effect on nerve conduction when administered perineurally to the sural nerve of healthy volunteers. Methods: Twenty-four informed healthy subjects were randomized into four equal groups [Saline (placebo), 0.5% tramadol, 1% tramadol and 1.5% tramadol]. The study was designed to be double-blinded. Sensory nerve action potentials were recorded electroneurographically. Two milliliters of study solution was administered to the sural nerve perineurally at the level of the ankle with the guidance of a nerve stimulator. A sensory block was assumed to have developed when the amplitude of the averaged sensory nerve action potentials diminished below 80% of the baseline value in the subsequent recordings. Results: According to the electroneurographical recordings, none of the volunteers in the saline group had block. However, the block rates with 0.5%, 1% and 1.5% tramadol were 1/6, 4/6 and 6/6, respectively (p<0.05). The maximum decrement in the sensory action potential amplitudes with respect to baseline amplitudes (given as median values) were as follows: 7.8% with saline; 12.5% with 0.5% tramadol; 38.5% with 1% tramadol; and 77.5% with 1.5% tramadol (p<0.05). While the median duration of sensory block with 0.5% tramadol was 5 minutes, it was 15 minutes with 1% tramadol and 35 minutes with 1.5% tramadol. Conclusion: Perineurally administered tramadol blocks sensory nerve conduction of the sural nerve in a dose-dependent manner.