Effect of bupivacaine 0.25% and 0.5% on nociceptive, motor and proprioceptive function in an ultrasound-guided sciatic nerve block model in rats

To evaluate the nociceptive, motor and proprioceptive response after ultrasound-guided perineural sciatic nerve injections of bupivacaine 0.25% and 0.5% in Wistar rats. Prospective, randomized, blinded crossover study. Eight healthy adult female Wistar rats. Rats underwent isoflurane anesthesia and were given ultrasound-guided sciatic nerve injections of 0.1 mL of 0.25% or 0.5% bupivacaine, with a one week recovery period between injections. Nociceptive function [electronic von Frey, (grams, response)], motor function (grip test, gait response (1–3 scale)], and proprioceptive function [tactile placing (0–3 scale) and paw positioning (clubbed digits/normal splaying) were evaluated at baseline and at 5, 10, 20, 30, 40, 60, 90, 120, 180, 240, 300, and 360 minutes after anesthesia. Data were analyzed using mixed models with significance set at p < 0.05. Sciatic nerve blockade was effective from 20 minutes into recovery, with treatment, time, and interaction on nociceptive function being significant from 20 to 240 minutes ( p < 0.05). In Group 0.25%, sensory function peaked at 60 minutes [111.2 grams, 95% Confidence Interval (CI) 100.8–121.5] and returned to a baseline response at 240 minutes (55.5 grams, 95% CI: 45.2–65.9). Significant differences between treatment groups were observed from 5 to 240 minutes. Motor and proprioceptive functions were reduced at 20 minutes [median score: 1, interquartile range (IQR: 1)] and returned to baseline at 240 minutes. In Group 0.5%, sensory function peaked at 90 minutes (133.7 grams, 95% CI: 123.3–144.1) and returned to baseline (52.0 grams, 95% CI: 41.6–62.4) in 300 minutes. Motor and proprioceptive functions were reduced at 10 minutes [1 (IQR: 0.25)] and returned to baseline by 300 minutes. Both 0.25 and 0.5% bupivacaine concentrations produced effective sciatic nerve blockade in all rats, demonstrating a concentration-dependent effect on the duration and magnitude of nociceptive, motor, and proprioceptive block.