title: A randomized, triple-masked, active-controlled investigation of the relative effects of dose, concentration, and infusion rate for continuous popliteal-sciatic nerve blocks in volunteers.
abstract: BACKGROUND
  It remains unknown whether local anaesthetic dose is the only factor influencing continuous popliteal-sciatic nerve block effects, or whether concentration, volume, or both exert an influence as well.
  
  
  METHODS
  Bilateral sciatic catheters were inserted in volunteers (n=24). Catheters were randomly assigned to ropivacaine of either 0.1% (8 ml h(-1)) or 0.4% (2 ml h(-1)) for 6 h. The primary endpoint was the tolerance to transcutaneous electrical stimulation within the tibial nerve distribution at hour 6. Secondary endpoints included current tolerance at other time points and plantar flexion maximum voluntary isometric contraction (22 h total).
  
  
  RESULTS
  At hour 6, tolerance to cutaneous stimulation for limbs receiving 0.1% ropivacaine was [mean (standard deviation)] 27.0 (20.2) vs26.9 (20.4) mA for limbs receiving 0.4% [estimated mean difference 0.2 mA; 90% confidence interval (CI) -8.2 to 8.5; P=0.02 and 0.03 for lower and upper boundaries, respectively]. Because the 90% CI fell within the prespecified tolerance ±10 mA, we conclude that the effect of the two concentration/volume combinations were equivalent. Similar negative findings were found for the secondary outcomes.
  
  
  CONCLUSIONS
  For continuous popliteal-sciatic nerve blocks, we found no evidence that local anaesthetic concentration and volume influence block characteristics, suggesting that local anaesthetic dose (mass) is the primary determinant of perineural infusion effects in this anatomic location. These findings suggest that for ambulatory perineural local anaesthetic infusion-for which there is usually a finite local anaesthetic reservoir-decreasing the basal rate while increasing the local anaesthetic concentration may allow for increased infusion duration without compromising postoperative analgesia.
  
  
  BACKGROUND
  NCT01898689.
authors.affiliation: Department of Anesthesiology, University of California San Diego, 200 West Arbor Drive, MC 8770, San Diego, CA 92103-8770, USA.
authors.forename: S J
authors.initials: SJ
authors.lastname: Madison
authors.affiliation: Department of Anesthesiology, University of California San Diego, 200 West Arbor Drive, MC 8770, San Diego, CA 92103-8770, USA.
authors.forename: A M
authors.initials: AM
authors.lastname: Monahan
authors.affiliation: Department of Anesthesiology, University of California San Diego, 200 West Arbor Drive, MC 8770, San Diego, CA 92103-8770, USA.
authors.forename: R R
authors.initials: RR
authors.lastname: Agarwal
authors.affiliation: Department of Anesthesiology, University of California San Diego, 200 West Arbor Drive, MC 8770, San Diego, CA 92103-8770, USA.
authors.forename: T J
authors.initials: TJ
authors.lastname: Furnish
authors.affiliation: Department of Quantitative Health Sciences, Cleveland Clinic, Cleveland, OH, USA Department of Outcomes Research, Cleveland Clinic, Cleveland, OH, USA.
authors.forename: E J
authors.initials: EJ
authors.lastname: Mascha
authors.affiliation: Department of Quantitative Health Sciences, Cleveland Clinic, Cleveland, OH, USA Department of Outcomes Research, Cleveland Clinic, Cleveland, OH, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Xu
authors.affiliation: Division of Biostatistics and Bioinformatics, University of California San Diego, 200 West Arbor Drive, MC 8770, San Diego, CA 92103-8770, USA.
authors.forename: M C
authors.initials: MC
authors.lastname: Donohue
authors.affiliation: Department of Anesthesiology, University of California San Diego, 200 West Arbor Drive, MC 8770, San Diego, CA 92103-8770, USA.
authors.forename: A C
authors.initials: AC
authors.lastname: Morgan
authors.affiliation: Department of Anesthesiology, University of California San Diego, 200 West Arbor Drive, MC 8770, San Diego, CA 92103-8770, USA bilfeld@ucsd.edu.
authors.forename: B M
authors.initials: BM
authors.lastname: Ilfeld
mesh_terms: D000328:Adult; D000577:Amides / Q000008:administration & dosage / Q000494:pharmacology*; D000772:Anesthesia, Local / Q000379:methods*; D000779:Anesthetics, Local / Q000008:administration & dosage / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007260:Infusion Pumps; D008297:Male; D008875:Middle Aged; D009407:Nerve Block / Q000379:methods*; D010147:Pain Measurement / Q000379:methods*; D000077212:Ropivacaine; D012584:Sciatic Nerve / Q000187:drug effects*; D055815:Young Adult
chemical_list: D000577:Amides; D000779:Anesthetics, Local; D000077212:Ropivacaine
keywords: continuous peripheral nerve block; perineural infusion; perineural local anaesthetic infusion