Ultrasound guidance improves a continuous popliteal sciatic nerve block when compared with nerve stimulation

Background and objectives: Continuous sciatic nerve blockade at the popliteal level effectively alleviates postoperative pain after major foot and ankle surgery. No randomized controlled trials have previously compared the success rate of continuous sciatic nerve sensory blockade between ultrasound and nerve stimulation guidance. In the current study, we tested the hypothesis that ultrasound-guided catheter placement improves the success rate of continuous sciatic nerve sensory blockade compared with catheter placement with nerve stimulation guidance.

Methods: After research ethics committee approval and informed consent, 100 patients scheduled for elective major foot and ankle surgery were randomly allocated to popliteal catheter placement either with ultrasound or nerve stimulation guidance. The primary outcome was the success rate of sensory block the first 48 postoperative hours. Successful sensory blockade was defined as sensory loss in both the tibial and common peroneal nerve territories at 1, 6, 24, and 48 hrs postoperatively.

Results: The ultrasound group had significantly higher success rate of sensory block compared with the nerve stimulation group (94% versus 79%, P=0.03). Ultrasound compared with nerve stimulation guidance also entails reduced morphine consumption (median of 18 mg [range, 0-159 mg] versus 34 mg [range, 0-152 mg], respectively, P=0.02), fewer needle passes (median of 1 [range, 1-6] versus 2 [range, 1-10], respectively, P=0.0005), and greater patient satisfaction (median numeric rating scale 9 [range, 5-10] versus 8 [range, 3-10)] respectively, P=0.0006) during catheter placement.

Conclusion: Ultrasound guidance used for sciatic catheter placement improves the success rate of sensory block, number of needle passes, patient satisfaction during catheter placement, and morphine consumption compared with nerve stimulation guidance.