title: Plasma concentrations of ropivacaine following ultrasound-guided or nerve-stimulator-guided femoral nerve block: A prospective randomised study.
abstract: OBJECTIVE
  Our aim was to establish a plasma concentration curve for ropivacaine following femoral nerve blockade and to ascertain whether the resulting plasma concentrations differ significantly depending on whether neurostimulation (NS) or ultrasound (US) guidance was used.
  
  
  METHODS
  Sixteen male and female subjects aged 18 to 80 who were scheduled to undergo unilateral total knee replacement or anterior cruciate ligament reconstruction under general or spinal anaesthesia, and for whom a femoral nerve block was indicated for postoperative analgesia, were enrolled in this prospective, randomised study. Patients were randomised to undergo either US or NS-guidance femoral nerve blocks. All blocks were performed with 20 mL of 5mg/mL ropivacaine. Blood samples were drawn before the nerve block and 20, 30, 40, 50, 60, 70, and 80 minutes after the block. Plasma levels of ropivacaine were analysed by high performance liquid chromatography (HPLC).
  
  
  RESULTS
  All blocks were successful and no patient showed signs or symptoms of local anaesthetic toxicity. The plasma concentration of ropivacaine peaked at 30 minutes in both arms. There was no significant difference in peak levels between US and NS-guidance (0.325±0.186 versus 0.356±0.106 μg/mL). Cmax and tmax were very similar between groups (0.364±0.177 versus 0.344±0.127 μg/mL, 33.75±15.06 versus 31.25±13.56 min for US and NS, respectively).
  
  
  CONCLUSIONS
  Plasma concentrations of ropivacaine peak around 30 minutes after a femoral nerve block regardless of the technique used. No significant difference was found between US- and NS-guidance.
authors.affiliation: Baylor College of Medicine, 1, Baylor Plaza, MS: BCM-120, 77030 Houston, TX, United States.
authors.forename: Lisa K
authors.initials: LK
authors.lastname: Mouzi
authors.affiliation: John Jay College of Criminal Justice, CUNY, 524 West 59th Street, NY 10019 New York, United States.
authors.forename: Olivia
authors.initials: O
authors.lastname: Adams
authors.affiliation: NYU School of Medicine, 550, 1st Avenue, NY 10016 New York, United States.
authors.forename: Germaine
authors.initials: G
authors.lastname: Cuff
authors.affiliation: John Jay College of Criminal Justice, CUNY, 524 West 59th Street, NY 10019 New York, United States.
authors.forename: Elaan
authors.initials: E
authors.lastname: Lukasiewicz
authors.affiliation: John Jay College of Criminal Justice, CUNY, 524 West 59th Street, NY 10019 New York, United States.
authors.forename: Elise
authors.initials: E
authors.lastname: Champeil
authors.affiliation: NYU School of Medicine, 550, 1st Avenue, NY 10016 New York, United States. Electronic address: arthur.atchabahian@gmail.com.
authors.forename: Arthur
authors.initials: A
authors.lastname: Atchabahian
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000577:Amides / Q000097:blood*; D000779:Anesthetics, Local / Q000097:blood*; D059549:Anterior Cruciate Ligament Reconstruction / Q000379:methods; D019645:Arthroplasty, Replacement, Knee / Q000379:methods; D004558:Electric Stimulation; D005260:Female; D005267:Femoral Nerve / Q000000981:diagnostic imaging*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009407:Nerve Block / Q000379:methods*; D010149:Postoperative Pain / Q000188:drug therapy; D011446:Prospective Studies; D000077212:Ropivacaine; D018084:Ultrasonography, Interventional; D055815:Young Adult
chemical_list: D000577:Amides; D000779:Anesthetics, Local; D000077212:Ropivacaine
keywords: Femoral nerve block; High performance liquid chromatography; Local anaesthetic toxicity; Nerve-stimulator guidance; Ropivacaine; Ultrasound guidance