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ANALGESIA

Low Volume and High Concentration of Local Anesthetic Is More Efficacious than High Volume and Low Concentration in Labat's Sciatic Nerve Block: A Prospective, Randomized Comparison

Manuel Taboada Muñiz, MD, PhD^*, Jaime Rodríguez, MD, PhD^*, María Bermúdez, MD^*, Cristina Valiño, MD, Noemi Blanco, MD^*, Marcos Amor, MD^*, Pilar Aguirre, MD^*, Ana Masid, MD^*, Joaquin Cortes, MD, PhD^*, Julián Álvarez, MD, PhD^*, and Peter G. Atanassoff, MD

From the *Department of Anesthesiology, University of Santiago de Compostela, Hospital Clínico Universitario de Santiago, Spain; Department of Anesthesiology, Hospital Meixoeiro, CHUVI, Vigo, Spain; and Department of Anesthesiology, Yale University School of Medicine, New Haven, Connecticut.

Address correspondence and reprint requests to Manuel Taboada Muñiz, MD, PhD, Department of Anesthesiology, Hospital Clínico Universitario de Santiago, Travesía da Choupana s/n. 15706 Santiago de Compostela, Spain. Address e-mail to manutabo{at}yahoo.es.

Abstract

BACKGROUND: Various factors markedly affect the onset time and success rate, of peripheral nerve blockade. This prospective, randomized, double-blind study, compared a dose of mepivacaine 300 mg, in a 20 or 30 mL injection volume for sciatic nerve blockade using Labat's posterior approach.

METHODS: A total of 90 patients undergoing foot surgery were randomly allocated to receive sciatic nerve block with 20 mL of 1.5% mepivacaine (n = 45) or 30 mL of 1% mepivacaine (n = 45). All blocks were performed with the use of a nerve stimulator (stimulation frequency 2 Hz; intensity 1.5–0.5 mA). In the two groups, appropriate nerve stimulation was elicited at <0.5 mA and the targeted evoked motor response was plantar flexion of the foot. Time required for onset of sensory and motor block in the distribution of the tibial and common peroneal nerves were recorded. A successful block was defined as a complete loss of pinprick sensation in the sciatic nerve distribution with concomitant inability to perform plantar or dorsal flexion of the foot.

RESULTS: A greater success rate was observed with 20 mL of 1.5% mepivacaine (96.6%) than with 30 mL of 1% mepivacaine (68.9%; P < 0.05). Time to onset of complete sensory and motor block was shorter after injection of 20 mL of 1.5% mepivacaine (11 ± 6 min and 13 ± 7 min, respectively) than after 30 mL of 1% mepivacaine (17 ± 8 min and 19 ± 8 min, respectively, P < 0.05).

CONCLUSION: In Labat's sciatic nerve blockade, administering a low volume and a high concentration of local anesthetic (1.5% mepivacaine) is associated with a higher success rate and a shorter onset time than a high volume and a low concentration of solution (1% mepivacaine).

Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999