Femoral and sciatic nerve blockade of the pelvic limb with and without obturator nerve block for tibial plateau levelling osteotomy surgery in dogs.

Objective: To determine the effect of blocking the obturator nerve in addition to performing femoral nerve and sciatic nerve blocks on intraoperative nociception in dogs undergoing unilateral tibial plateau levelling osteotomy (TPLO) surgery.

Study Design: Prospective, blinded, randomized, placebo-controlled, clinical comparison.

Animals: A total of 88 client-owned dogs undergoing unilateral TPLO surgery (100 procedures).

Methods: Dogs were randomly assigned to either group FSO (femoral, sciatic and obturator nerve blocks) [n = 50; ropivacaine 0.75% (0.75 mg kg)] or group FSP (femoral, sciatic and placebo) [n = 50; ropivacaine 0.75% (0.75 mg kg) femoral and sciatic nerve blocks plus saline solution 0.9% (0.1 mL kg) as a placebo injection around the obturator nerve]. The anaesthetic protocol was standardized. Data collection included intraoperative cardiopulmonary variables and opioid consumption. Rescue analgesia consisted of an intravenous bolus of fentanyl (2 μg kg) and was administered when a change in cardiopulmonary variables (20% increase in mean arterial pressure or heart rate) was attributed to a sympathetic stimulus. Data were analysed using generalized linear mixed models, cross tables and multivariable binary logistic regression. Results were expressed as adjusted odds ratios with 95% confidence intervals and Wald p values (α = 0.05).

Results: There were no clinically relevant differences between groups in intraoperative cardiopulmonary variables and need for rescue analgesia. The requirement for rescue analgesia was significantly higher in dogs with a body weight >34 kg.

Conclusions And Clinical Relevance: Anaesthesia of the obturator nerve in addition to the femoral and sciatic nerves was not associated with clinically significant differences in cardiopulmonary variables or a reduced need for rescue analgesia. Therefore, the clinical benefit of an additional obturator nerve block for intraoperative antinociception in dogs undergoing unilateral TPLO surgery using the described anaesthetic regimen is low.