Sciatic nerve block in dogs: description and evaluation of a modified ultrasound-guided parasacral approach

To develop a modified ultrasound-guided parasacral approach to the sciatic nerve and compare the effects of a volume of 0.2 mL kg^-1 of 0.5% levobupivacaine with an equivalent volume of 0.9% saline injected near the sciatic nerve.

Cadaveric and experimental, blinded, randomized study.

Seven canine cadavers and seven experimental Beagle dogs.

Both sciatic nerves of seven cadavers were identified using a modified in-plane ultrasound-guided approach. Methylene blue solution (0.2 mL) was injected perineurally, and success was evaluated through dissection. The same approach was repeated in seven Beagle dogs sedated with dexmedetomidine (50 μg kg^-1) injected intramuscularly (IM). After randomization, 0.2 mL kg^-1 of 0.5% levobupivacaine (limb L) and 0.2 mL kg^-1 of 0.9% saline (limb C) were injected perineurally on either right or left limb. Block success was determined by sensory deficits every hour for 8 hours after an atipamezole injection (0.2 mg kg^-1) IM. Reaction to pinprick (binary score) over the course of the sciatic nerve (four locations) and locomotion were assessed.

The overall sciatic nerve block success was 93% in cadavers and 86% in sedated dogs. It was impossible to localize the sciatic nerves in one obese sedated dog. Significant differences between limb L and limb C were observed for pinprick at great trochanter, caudal thigh and lateral tarsal joint (p < 0.0001). Reaction to pinprick was absent in all dogs at great trochanter and caudal thigh up to at least 3 hours on limb L. Locomotion was impaired in all but one dog for 60 (30-210) minutes (median; interquartile range). No complications were observed.

A volume of ≥0.2 mL kg^-1 and a concentration of 0.5% levobupivacaine can be recommended when using a modified ultrasound-guided parasacral approach to the sciatic nerve in dogs.