title: 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.
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).
  
  
  CONCLUSIONS
  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).
authors.affiliation: Department of Anesthesiology, Hospital Clínico Universitario de Santiago, Travesía da Choupana s/n. 15706 Santiago de Compostela, Spain. manutabo@yahoo.es
authors.forename: Manuel
authors.initials: M
authors.lastname: Taboada Muñiz
authors.forename: Jaime
authors.initials: J
authors.lastname: Rodríguez
authors.forename: María
authors.initials: M
authors.lastname: Bermúdez
authors.forename: Cristina
authors.initials: C
authors.lastname: Valiño
authors.forename: Noemi
authors.initials: N
authors.lastname: Blanco
authors.forename: Marcos
authors.initials: M
authors.lastname: Amor
authors.forename: Pilar
authors.initials: P
authors.lastname: Aguirre
authors.forename: Ana
authors.initials: A
authors.lastname: Masid
authors.forename: Joaquin
authors.initials: J
authors.lastname: Cortes
authors.forename: Julián
authors.initials: J
authors.lastname: Alvarez
authors.forename: Peter G
authors.initials: PG
authors.lastname: Atanassoff
mesh_terms: D000328:Adult; D000368:Aged; D000779:Anesthetics, Local / Q000008:administration & dosage*; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D008297:Male; D008619:Mepivacaine / Q000008:administration & dosage*; D008875:Middle Aged; D009407:Nerve Block / Q000379:methods*; D011446:Prospective Studies; D012584:Sciatic Nerve
chemical_list: D000779:Anesthetics, Local; D008619:Mepivacaine