Effect of temperature‐responsive hydrogel on femoral and sciatic nerve blocks using bupivacaine in Beagle dogs

Objectives To compare the duration of regional anesthesia of the pelvic limb using bupivacaine with and without a temperature‐responsive hydrogel (TRH) in dogs. Methods Under anesthesia using medetomidine (10 μg·kg−1), alfaxalone (2 mg·kg−1), and isoflurane, seven healthy male Beagles received four injections of 0.5% bupivacaine (1 mg·kg−1 with 5 μg·ml−1 epinephrine) to block the femoral and sciatic nerves bilaterally via ultrasound with nerve stimulation guidance. Bupivacaine was used on one pelvic limb (Bup treatment), and bupivacaine with TRH was used on the contralateral limb (Bup‐TRH treatment). The nerve block was considered successful upon the absence of responses to pinching the digital pads and mid‐tibial skin of both pelvic limbs with mosquito forceps; the pinch, proprioception, and locomotion tests were performed before (baseline) and at each hour after the nerve block until sensory and motor functions returned to baseline. The effect of TRH on nerve blocks was analyzed using a linear mixed model. Results The duration of the sensory nerve block at the digital pads and mid‐tibial skin was longer with Bup‐TRH (8.0 ± 1.6 h and 10.9 ± 1.6 h, respectively) than with Bup treatment (3.7 ± 2.0 h and 8.0 ± 1.6 h, respectively). Motor block times of proprioception and locomotion were longer with Bup‐TRH (9.3 ± 1.6 and 12.7 ± 1.5 h, respectively) than with Bup treatment (4.6 ± 1.9 and 9.6 ± 1.5 h, respectively). No complications were observed. Clinical significance TRH extended the duration of regional anesthesia of the pelvic limb using bupivacaine. Recent developed temperature‐responsive hydrogel, PF‐72®, was applied to extend the duration of regional anesthesia of the pelvic limb using bupivacaine. Significantly longer nerve block duration was confirmed when bupivacaine was used in combination with PF‐72® than it was used alone.