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Regional Anesthesia & Pain Medicine:
doi: 10.1097/AAP.0000000000000051
Original Articles

Minimum Effective Volume of Combined Lidocaine-Bupivacaine for Analgesic Subparaneural Popliteal Sciatic Nerve Block

Techasuk, Wallaya MD*; Bernucci, Francisca MD; Cupido, Tracy DO, FRCPC*; González, Andrea P. MD; Correa, José A. PhD; Finlayson, Roderick J. MD, FRCPC*; Tran, De Q.H. MD, FRCPC*

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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).

Copyright © 2014 by American Society of Regional Anesthesia and Pain Medicine.

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