A RAT SCIATIC-NERVE MODEL FOR INDEPENDENT ASSESSMENT OF SENSORY AND MOTOR BLOCK INDUCED BY LOCAL-ANESTHETICS

The purpose of this study was to develop a reliable model to independe ntly quantify motor and sensory block produced by local anesthetics. T he sciatic nerve was blocked in 52 rats by injecting 0.2 mL of 0.125%, 0.25%, 0.5%, or 0.75% bupivacaine (n = 13 for each concentration). Ac curate needle placement was achieved using a nerve stimulator at 0.2 m A and 1 Hz. Ten control rats received 0.9% saline (n = 5) or sham nerv e stimulation (n = 5). Motor block was assessed by measuring hindpaw g rip strength with a dynamometer. Sensory block was determined by measu ring hindpaw withdrawal latency from radiant heat. The intensity of bo th motor and sensory block measured at 30-min intervals was plotted ag ainst time until full recovery to obtain the area under the curve. Int ergroup comparisons using analysis of variance showed increasing area under the curve with increasing concentrations of bupivacaine for moto r blocks (P < 0.05 for all intergroup comparisons except 0.5% vs 0.75% ) and sensory blocks (P < 0.05 for all intergroup comparisons). Normal saline or sham nerve stimulation did not result in any motor or senso ry block.