title: Ropivacaine plasma concentrations are similar during continuous lumbar plexus blockade using the anterior three-in-one and the posterior psoas compartment techniques.
abstract: OBJECTIVE
  To compare ropivacaine blood concentrations obtained after a continuous lumbar plexus block performed either by the anterior three-in-one femoral (FEM) technique or the posterior (psoas compartment; PSOAS) technique.
  
  
  METHODS
  As a substudy of a larger clinical trial, 24 patients were randomly allocated to receive a bolus of 30 mL of ropivacaine 0.5% plus epinephrine 1:200,000 followed by an infusion of ropivacaine 0.2% at 12 mL.hr(-1) for 48 hr via one of the two continuous lumbar plexus block techniques. Plasma ropivacaine concentrations, up to 48 hr, were measured by high performance liquid chromatography.
  
  
  RESULTS
  Mean plasma ropivacaine concentrations were higher in the PSOAS group at 15, 30, and 60 min (two-way analysis of variance, P < 0.0001) but areas under the curve were similar for both groups (FEM 452.4 +/- 253.6 mg.hr(-1).L(-1), PSOAS 433.4 +/- 99.0 mg.hr(-1).L(-1)). Mean maximal plasma concentrations were observed at 48 hr and were comparable for the two techniques (FEM 2630.9 +/- 1470.3 ng.L(-1), PSOAS 2325.1 +/- 604.2 ng.mL(-1)). There was no correlation between blood concentrations at 48 hr and body weight (r2 = 0.085, P = 0.21). One patient in the FEM group achieved a concentration of 6201 ng.mL(-1) at 48 hr.
  
  
  CONCLUSIONS
  Although the posterior PSOAS block results in higher early plasma concentrations of local anesthetic than the anterior three-in-one FEM block, both techniques are equivalent with regards to their potential toxicity when a continuous infusion is administered. Local anesthetic accumulation occurs with an infusion of ropivacaine 0.2% at 12 mL.hr(-1) and can lead to potentially dangerous concentrations at 48 hr.
authors.affiliation: Department of Anesthesiology, Maisonneuve-Rosemont Hospital, Montréal, Québec, Canada.
authors.forename: Ismail
authors.initials: I
authors.lastname: Kaloul
authors.forename: Joanne
authors.initials: J
authors.lastname: Guay
authors.forename: Christiane
authors.initials: C
authors.lastname: Côté
authors.forename: Antoine
authors.initials: A
authors.lastname: Halwagi
authors.forename: France
authors.initials: F
authors.lastname: Varin
mesh_terms: D000328:Adult; D000368:Aged; D000577:Amides / Q000097:blood*; D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000627:therapeutic use; D000779:Anesthetics, Local / Q000097:blood*; D002851:Chromatography, High Pressure Liquid; D004837:Epinephrine; D005260:Female; D006801:Humans; D008160:Lumbosacral Plexus; D008297:Male; D008875:Middle Aged; D009020:Morphine / Q000008:administration & dosage / Q000627:therapeutic use; D009407:Nerve Block; D010147:Pain Measurement / Q000187:drug effects; D010149:Postoperative Pain / Q000188:drug therapy; D000077212:Ropivacaine; D014662:Vasoconstrictor Agents
chemical_list: D000577:Amides; D000701:Analgesics, Opioid; D000779:Anesthetics, Local; D014662:Vasoconstrictor Agents; D009020:Morphine; D000077212:Ropivacaine; D004837:Epinephrine