Intraneural Ultrasound-guided Sciatic Nerve Block: Minimum Effective Volume and Electrophysiologic Effects. (August 2018)

• Record Type: Journal Article
• Authors: Cappelleri, Gianluca; Ambrosoli, Andrea Luigi; Gemma, Marco; Cedrati, Valeria Libera Eva; Bizzarri, Federico; Danelli, Giorgio Francesco
• Is Part Of: Anesthesiology. Volume 129:Number 2(2018)
• Publication Date: 2018-08
• Subjects: Anesthesiology -- Periodicals; Anesthetics -- Periodicals; Anesthesia -- Periodicals; 617.9605
• DOI: 10.1097/ALN.0000000000002254
• Languages: English
• ISSNs: 0003-3022

Abstract

Abstract : What We Already Know about This Topic: Reducing the volume of local anesthetic administered for neural blockade may increase safety Local anesthetic administration can result in nerve damage What This Article Tells Us That Is New: The low volume intraneural injection of ropivacaine 1% provided complete sensory-motor nerve block Reductions in action potential amplitudes lasting at least 6 months from the time of nerve block suggest that additional safety studies will be required Background: Both extra- and intraneural sciatic injection resulted in significant axonal nerve damage. This study aimed to establish the minimum effective volume of intraneural ropivacaine 1% for complete sensory-motor sciatic nerve block in 90% of patients, and related electrophysiologic variations. Methods: Forty-seven consecutive American Society of Anesthesiologists physical status I-II patients received an ultrasound-guided popliteal intraneural nerve block following the up-and-down biased coin design. The starting volume was 15 ml. Baseline, 5-week, and 6-month electrophysiologic tests were performed. Amplitude, latency, and velocity were evaluated. A follow-up telephone call at 6 months was also performed. Results: The minimum effective volume of ropivacaine 1% in 90% of patients for complete sensory-motor sciatic nerve block resulted in 6.6 ml (95% CI, 6.4 to 6.7) with an onset time of 19 ± 12 min. Success rate was 98%. Baseline amplitude of action potential (mV) at ankle, fibula, malleolus, and popliteus were 8.4 ± 2.3, 7.1 ± 2.0, 15.4 ± 6.5, and 11.7 ± 5.1 respectively. They were significantly reduced at the fifth week (4.3 ± 2.1, 3.5 ± 1.8, 6.9 ± 3.7, and 5.2 ± 3.0) and at the sixth month (5.9 ± 2.3, 5.1 ± 2.1, 10.3 ± 4.0, and 7.5 ± 2.7) ( P < 0.001 in all cases). Latency and velocity did not change from the baseline. No patient reported neurologic symptoms at 6-month follow-up. Conclusions: The intraneural ultrasound-guided popliteal local anesthetic injection significantly reduces the local anesthetic dose to achieve an effective sensory-motor block, decreasing the risk of systemic toxicity. Persistent electrophysiologic changes suggest possible axonal damage that will require further investigation. Abstract : The low volume intraneural injection of ropivacaine 1% provided complete sensory-motor nerve block. Reductions in action potential amplitudes lasting at least 6 months from the time of nerve block suggest that additional safety studies will be required.