Ultrasound-guided femoral and obturator nerves block in the psoas compartment in dogs: anatomical and randomized clinical study

Abstract

Objective: To evaluate intraoperative and postoperative efficacy of ultrasound (US)-guided femoral (FN) and obturator (ON) nerves block, in the iliopsoas muscle compartment (IPM), using an in-plane technique.

Study design: Anatomical research and randomized, prospective, 'blinded' clinical study.

Animals: Six dog cadavers and 20 client-owned dogs undergoing tibial plateau levelling osteotomy (TPLO) surgery.

Methods: In phase 1, anatomical dissections and US imaging of the IPM were performed to design an US-guided nerve block involving the FN and ON simultaneously. The technique was considered successful if new methylene blue solution injection (0.1 mL kg^-1) stained FN-ON for ≥2 cm. In phase 2, the US-guided nerve block designed in phase 1, combined with US-guided sciatic nerve (ScN) block, was performed in 20 dogs undergoing TPLO surgery. Patients were assigned randomly to one of two treatment groups: ropivacaine 0.3% (R3, n=10) and ropivacaine 0.5% (R5, n=10) at a volume of 0.1 mL kg^-1 for each nerve block. Intraoperative success rate (fentanyl requirement < 2.1 mcg kg^-1 hour^-1) and postoperative pain score [Short Form-Glasgow Composite Measure Pain Scale (SF-GCMPS) ≥ 5/20] were evaluated.

Results: In phase 1, the US image of FN-ON was detected between L6 and L7. In-plane needling technique produced a staining of >4 cm in six of six cases. No abdominal or epidural dye spread was found. In phase 2, median fentanyl infusion rates were 0.5 (0.0-0.9) μg kg^-1 hour^-1 for R3 and 0.6 (0.0-2.2) μg kg^-1 hour^-1 for R5. At 9 and 11 hours after the peripheral nerve blocks, an SF-GCMPS ≥ 5 was observed for R3 and R5, respectively.

Conclusions and clinical relevance: The US-guided FN-ON block in the IPM, using an in-plane technique, combined with US-guided ScN block, provided sufficient analgesia to minimize the use of fentanyl during TPLO surgery. A longer postoperative analgesia was observed in group R5 compared with R3.

Keywords: dog; femoral nerve; locoregional anaesthesia; obturator nerve; ultrasound.