Phenol block of peripheral nerve conduction: Titrating for optimum effect

Objectives: To verify the dose-response relationship in phenol nerve block and to determine the concentration and volume of phenol injectate required for effective nerve conduction block. Design: Before-after, experimental study. Setting: A research institute laboratory. Animals: Seventy-one New Zealand white rabbits. Interventions: Group I (n = 48) received tibial nerve block by perineural i njection (phenol, n = 40; saline, n = 8), group II (n = 21) by submerging t he nerve in phenol solution. The 6 subgroups of group I each received diffe rent concentrations (3%, 4%, 5%) and volumes (0.1mL, 0.2mL, 0.3mL). The 2 s ubgroups of group II received 3% (n = 8) and 5% (n = 13) phenol. Main Outcome Measures: Compound muscle action potential (CMAP) and tension of triceps surae muscles by electric stimulation of the sciatic nerve were measured preintervention and at day 1, and weeks 1, 2, 4, and 8 postblock. Histologic studies were performed on 2 animals from group I. Results: Two rabbits in group I died before results were obtained. In the r emaining animals, CMAP amplitude reduced significantly (p < .05) as the vol ume of 5% phenol solution increased from 0.1mL, 0.2mL, to 0.3mL. A high con centration of phenol produced a more pronounced conduction block; however, no significant (p = .0589) difference existed among the 3 concentrations. S ubmerged tibial nerve had a greater degree of conduction block than perineu rally injected nerve. Depth of the degeneration area in nerve fascicle vari ed with distance from the injection point. Conclusions: The nerve block effect of phenol can be titrated by adjusting the concentration and volume of phenol solution if the technique of applica tion and localization of a block site are standardized.