Minimum effective volume of combined lidocaine-bupivacaine for analgesic subparaneural popliteal sciatic nerve block.
OBJECTIVE
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).
From the *Montreal General Hospital, Department of Anesthesia, McGill University, Montreal, Quebec, Canada; †Hospital de Carabineros, Department of Anesthesia, Santiago, Chile; and ‡Department of Mathematics and Statistics, McGill University, Montreal, Quebec, Canada.
Wallaya
W
Techasuk
Francisca
F
Bernucci
Tracy
T
Cupido
Andrea P
AP
González
José A
JA
Correa
Roderick J
RJ
Finlayson
De Q H
DQ
Tran
D000328:Adult; D000698:Analgesia / Q000379:methods*; D000779:Anesthetics, Local / Q000008:administration & dosage*; D002045:Bupivacaine / Q000008:administration & dosage*; D004338:Drug Combinations; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008012:Lidocaine / Q000008:administration & dosage*; D008297:Male; D008875:Middle Aged; D009407:Nerve Block / Q000379:methods*; D011446:Prospective Studies; D012584:Sciatic Nerve / Q000187:drug effects* / Q000502:physiology; D016896:Treatment Outcome; D018084:Ultrasonography, Interventional / Q000379:methods
D000779:Anesthetics, Local; D004338:Drug Combinations; D008012:Lidocaine; D002045:Bupivacaine