title: Increasing the injection volume by dilution improves the onset of motor blockade, but not sensory blockade of ropivacaine for brachial plexus block.
abstract: OBJECTIVE
  Ropivacaine used for axillary plexus block provides effective motor and sensory blockade. Varying clinical dosage recommendations exist. Increasing the dosage by increasing the concentration showed no improvement in onset. We compared the behaviour of a constant dose of ropivacaine 150 mg diluted in a 30, 40 or 60 mL injection volume for axillary (brachial) plexus block.
  
  
  METHODS
  A prospective, randomized, observer-blinded study on patients undergoing elective hand surgery was conducted in a community hospital. Three groups of patients with a constant dose of ropivacaine 150 mg, diluted in 30,40 or 60 mL NaCl 0.9%, for axillary plexus blockade were compared for onset times of motor and sensory block onset by assessing muscle strength, two-point discrimination and constant-touch sensation.
  
  
  RESULTS
  Increasing the injection volume of ropivacaine 150 mg to 60 mL led to a faster onset of motor block, but not of sensory block, in axillary plexus block, compared with 30 or 40 mL volumes of injection.
  
  
  CONCLUSIONS
  The data show that the onset of motor, but not of sensory block, is accelerated by increasing the injection volume to 60 mL using ropivacaine 150 mg for axillary plexus block. This may be useful for a more rapid determination of whether the brachial plexus block is effective. However, when performing surgery in the area of the block, sensory block onset seems more important.
authors.affiliation: Department of Anaesthesia and Critical Care, City Hospital, Lainz, Vienna, Austria. herbert.krenn@chello.at
authors.forename: H
authors.initials: H
authors.lastname: Krenn
authors.forename: E
authors.initials: E
authors.lastname: Deusch
authors.forename: B
authors.initials: B
authors.lastname: Balogh
authors.forename: H
authors.initials: H
authors.lastname: Jellinek
authors.forename: W
authors.initials: W
authors.lastname: Oczenski
authors.forename: E
authors.initials: E
authors.lastname: Plainer-Zöchling
authors.forename: R D
authors.initials: RD
authors.lastname: Fitzgerald
mesh_terms: D000577:Amides / Q000008:administration & dosage*; D000779:Anesthetics, Local / Q000008:administration & dosage*; D001917:Brachial Plexus; D004311:Double-Blind Method; D004558:Electric Stimulation; D005260:Female; D006225:Hand / Q000601:surgery*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009046:Motor Neurons / Q000187:drug effects; D009119:Muscle Contraction; D009407:Nerve Block; D009475:Neurons, Afferent / Q000187:drug effects; D011446:Prospective Studies; D000077212:Ropivacaine; D012677:Sensation; D014110:Touch
chemical_list: D000577:Amides; D000779:Anesthetics, Local; D000077212:Ropivacaine