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Minimum Effective Volume of Combined Lidocaine-Bupivacaine for Analgesic Subparaneural Popliteal Sciatic Nerve Block
  1. Wallaya Techasuk, MD*,
  2. Francisca Bernucci, MD,
  3. Tracy Cupido, DO, FRCPC*,
  4. Andrea P. González, MD,
  5. José A. Correa, PhD,
  6. Roderick J. Finlayson, MD, FRCPC* and
  7. De Q.H. Tran, MD, FRCPC*
  1. *Montreal General Hospital, Department of Anesthesia, McGill University, Montreal, Quebec, Canada
  2. Hospital de Carabineros, Department of Anesthesia, Santiago, Chile
  3. Department of Mathematics and Statistics, McGill University, Montreal, Quebec, Canada
  1. Address correspondence to: De Q.H. Tran, MD, FRCPC, Montreal General Hospital, Department of Anesthesia 1650 Ave Cedar, D10-144, Montreal, Quebec, Canada H3G 1A4 (e-mail: de_tran{at}hotmail.com).

Abstract

Background and Objectives The aim of this study was to determine the minimum effective volume (MEV) of combined lidocaine 1.0%–bupivacaine 0.25% with epinephrine 5 μg/mL in 90% of patients (MEV90) for ultrasound-guided subparaneural popliteal sciatic nerve block.

Methods All subjects received an ultrasound-guided subparaneural popliteal sciatic nerve block (at the neural bifurcation) with combined lidocaine 1.0%–bupivacaine 0.25% and epinephrine 5 μg/mL. Using an out-of-plane technique, a 17-gauge, 8-cm Tuohy needle was advanced until its tip was positioned between the tibial and peroneal nerves inside the paraneural sheath. Volume assignment was carried out using a biased coin design, up-and-down sequential method, where the volume of local anesthetic administered to each patient depended on the response of the previous one. In case of failure, the next subject received a higher volume (defined as the previous volume with an increment of 3.0 mL). If the previous patient had a successful block, the next subject was randomized to a lower volume (defined as the previous volume with a decrement of 3.0 mL), with a probability of b = 0.11, or the same volume, with a probability of 1 – b = 0.89. Using a composite scale encompassing sensory and motor block, success was defined, at 30 minutes, as a minimal score of 6 points (out of 8 points). The 6-point score was intended to mirror successful postoperative analgesia. Patients undergoing surgery of the leg, ankle, or foot were prospectively enrolled until 45 successful blocks were obtained.

Results Fifty-two patients were recruited for this study. Using isotonic regression and bootstrap confidence interval, the MEV90 of combined lidocaine 1.0%–bupivacaine 0.25% with epinephrine 5 μg/mL was estimated to be 13.3 mL (95% confidence interval, 10.2–16.4 mL).

Conclusions For ultrasound-guided subparaneural (analgesic) popliteal sciatic nerve block, the MEV90 of combined lidocaine 1.0%–bupivacaine 0.25% with epinephrine 5 μg/mL is 13.3 mL (95% confidence interval, 10.2–16.4 mL).

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Footnotes

  • The authors declare no conflict of interest.

    None of the authors received funding for this study.

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