Newly Published
Perioperative Medicine  |   May 2018
Intraneural Ultrasound-guided Sciatic Nerve Block: Minimum Effective Volume and Electrophysiologic Effects
Author Notes
  • From the Anesthesia, Intensive Care and Pain Therapy, AUSL, IRCCS (Scientific Research and Care Institute), Reggio Emilia, Italy (G.C., F.B., G.F.D.); the Anesthesia, Intensive Care and Pain Therapy, Ospedale di Circolo, Varese, Italy (A.L.A.); the Anesthesia and Intensive Care, IRCCS Ospedale San Raffaele, Italy (M.G.); and the Anesthesia and Pain Therapy, ASST Gaetano Pini-CTO, Milano, Italy (V.L.E.C.).
  • Submitted for publication November 2, 2017. Accepted for publication April 11, 2018.
    Submitted for publication November 2, 2017. Accepted for publication April 11, 2018.×
  • Acknowledgments: Mario Loiero, M.D., neurologist of the ASST Gaetano Pini-CTO of Milan (Milan, Italy), performed all electrophysiologic tests.
    Acknowledgments: Mario Loiero, M.D., neurologist of the ASST Gaetano Pini-CTO of Milan (Milan, Italy), performed all electrophysiologic tests.×
  • Research Support: Support was provided solely from institutional and/or departmental sources.
    Research Support: Support was provided solely from institutional and/or departmental sources.×
  • Competing Interests: The authors declare no competing interests.
    Competing Interests: The authors declare no competing interests.×
  • Reproducible Science: Full protocol available at: gianluca.cappelleri@ausl.re.it. Raw data available at: gianluca.cappelleri@ausl.re.it.
    Reproducible Science: Full protocol available at: gianluca.cappelleri@ausl.re.it. Raw data available at: gianluca.cappelleri@ausl.re.it.×
  • Correspondence: Address correspondence to Dr. Cappelleri: Anesthesia, Intensive Care, and Pain Therapy, ASM-IRCCS Arcispedale Santa Maria Nuova, Viale Risorgimento 80, 42123 Reggio Emilia RE, Italy. gianluca.cappelleri@ausl.re.it. Information on purchasing reprints may be found at www.anesthesiology.org or on the masthead page at the beginning of this issue. Anesthesiology’s articles are made freely accessible to all readers, for personal use only, 6 months from the cover date of the issue.
Article Information
Perioperative Medicine / Radiological and Other Imaging / Regional Anesthesia
Perioperative Medicine   |   May 2018
Intraneural Ultrasound-guided Sciatic Nerve Block: Minimum Effective Volume and Electrophysiologic Effects
Anesthesiology Newly Published on May 14, 2018. doi:10.1097/ALN.0000000000002254
Anesthesiology Newly Published on May 14, 2018. doi:10.1097/ALN.0000000000002254
Abstract

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.