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

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, âblindedâ 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 kgâ1) stained FNâON for â¥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 kgâ1for each nerve block. Intraoperative success rate (fentanyl requirement < 2.1 mcg kgâ1hourâ1) 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 FNâON 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 (0.0â0.9) μg kgâ1hourâ1for R3 and 0.6 (0.0â2.2) μg kgâ1hourâ1for 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 FNâON 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