Intraneural Ultrasound-guided Sciatic Nerve Block: Minimum Effective Volume and Electrophysiologic Effects

Area of Science:

• Anesthesiology
• Neurology
• Ultrasound-guided procedures

Background:

• Intraneural and extraneural sciatic injections can cause significant axonal nerve damage.
• Determining optimal local anesthetic volumes is crucial for effective nerve blocks and minimizing toxicity.

Purpose of the Study:

• To establish the minimum effective volume of intraneural ropivacaine 1% for a complete sensory-motor sciatic nerve block in 90% of patients.
• To evaluate related electrophysiologic variations following the injection.

Main Methods:

• Forty-seven patients received ultrasound-guided popliteal intraneural nerve blocks using a biased coin design.
• Electrophysiologic tests (amplitude, latency, velocity) were conducted at baseline, 5 weeks, and 6 months.
• A 6-month follow-up assessed for neurologic symptoms.

Main Results:

• The minimum effective volume for a 90% success rate was 6.6ml (95% CI, 6.4-6.7ml) with a 19±12 min onset.
• Action potential amplitude was significantly reduced at 5 weeks and 6 months (P < 0.001).
• No significant changes in latency or velocity were observed, and no patients reported neurologic symptoms at 6 months.

Conclusions:

• Ultrasound-guided intraneural popliteal injection effectively reduces local anesthetic dose, lowering systemic toxicity risk.
• Persistent electrophysiologic changes suggest potential axonal damage requiring further research.