title: Estimation and pharmacodynamic consequences of the minimum effective anesthetic volumes for median and ulnar nerve blocks: a randomized, double-blind, controlled comparison between ultrasound and nerve stimulation guidance.
abstract: BACKGROUND
  Nerve stimulation and ultrasound guidance are the most popular techniques for peripheral nerve blocks. However, the minimum effective anesthetic volume (MEAV) in selected nerves for both techniques and the consequences of decreasing the local anesthetic volume on the pharmacodynamic characteristics of nerve block remain unstudied. We designed a randomized, double-blind controlled comparison between neurostimulation and ultrasound guidance to estimate the MEAV of 1.5% mepivacaine and pharmacodynamics in median and ulnar nerve blocks.
  
  
  METHODS
  Patients scheduled for carpal tunnel release were randomized to ultrasound guidance (UG) or neurostimulation (NS) groups. A step-up/step-down study model (Dixon method) was used to determine the MEAV with nonprobability sequential dosing based on the outcome of the previous patient. The starting dose of 1.5% mepivacaine was 13 and 11 mL for median and ulnar nerves at the humeral canal. Block success/failure resulted in a decrease/increase of 2 mL. A blinded physician assessed sensory blockade at 2-minute intervals for 20 minutes. Block onset time and duration were noted.
  
  
  RESULTS
  The MEAV50 (SD) of the median nerve was lower in the UG group 2 (0.1) mL (95% confidence interval [CI] = [1, 96] to [2, 04]) than in the NS group 4 (3.8) mL (95% CI = [2, 4] to [5, 6]) (P = 0.017). There was no difference for the ulnar nerve between UG group 2 (0.1) mL (95% CI = [1, 96] to [2, 04]) and NS group 2.4 (0.6) mL (95% CI = [2, 1] to [2, 7]). The duration of sensory blockade was significantly correlated to local anesthetic volume, but onset time was not modified.
  
  
  CONCLUSIONS
  Ultrasound guidance selectively provided a 50% reduction in the MEAV of mepivacaine 1.5% for median nerve sensory blockade in comparison with neurostimulation. Decreasing the local anesthetic volume can decrease sensory block duration but not onset time.
authors: Department of Anesthesiology, Lapeyronie University Hospital, Route de Ganges, France.
authors: Matthieu
authors: M
authors: Ponrouch
authors: Nicolas
authors: N
authors: Bouic
authors: Sophie
authors: S
authors: Bringuier
authors: Philippe
authors: P
authors: Biboulet
authors: Olivier
authors: O
authors: Choquet
authors: Michèle
authors: M
authors: Kassim
authors: Nathalie
authors: N
authors: Bernard
authors: Xavier
authors: X
authors: Capdevila
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000779:Anesthetics, Local / Q000494:pharmacology; D002349:Carpal Tunnel Syndrome / Q000503:physiopathology / Q000601:surgery*; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000502:physiology; D008875:Middle Aged; D009407:Nerve Block / Q000706:statistics & numerical data; D011446:Prospective Studies; D004561:Transcutaneous Electric Nerve Stimulation / Q000706:statistics & numerical data; D016896:Treatment Outcome; D014459:Ulnar Nerve / Q000502:physiology; D018084:Ultrasonography, Interventional / Q000706:statistics & numerical data; D055815:Young Adult
chemical_list: D000779:Anesthetics, Local