title: Minimum effective local anaesthetic dose of isobaric levobupivacaine and ropivacaine administered via a spinal catheter for hip replacement surgery.
abstract: BACKGROUND
  Continuous spinal anaesthesia with spinal catheters allows incremental dosing of local anaesthetic and, consequently, less haemodynamic changes. However, little is known about the required doses. Therefore, we designed a study to assess the minimum effective local anaesthetic dose (MLAD) of levobupivacaine and ropivacaine in this context.
  
  
  METHODS
  Forty-one patients undergoing hip replacement surgery were randomly allocated to one of the two local anaesthetic groups in a double-blind manner. The initial dose of local anaesthetic was determined by the response of the previous patient: the effective dose resulted in a 1 mg decrease in the dose of levobupivacaine or ropivacaine, and an ineffective dose resulted in a 1 mg increase. The MLAD was calculated by the Dixon up-and-down method.
  
  
  RESULTS
  The MLAD of levobupivacaine was 11.7 mg (95% CI, 11.1-12.4) and that of ropivacaine 12.8 mg (95% CI, 12.2-13.4).
  
  
  CONCLUSIONS
  These doses are significantly smaller than doses reported before for single-shot spinal anaesthesia. Continuous spinal anaesthesia allows the use of relatively small doses of local anaesthetic.
authors.affiliation: Department of Anaesthesia and Intensive Care, Tartu University Clinics, Tartu, Estonia. andres.sell@kliinikum.ee
authors.forename: A
authors.initials: A
authors.lastname: Sell
authors.forename: K T
authors.initials: KT
authors.lastname: Olkkola
authors.forename: J
authors.initials: J
authors.lastname: Jalonen
authors.forename: R
authors.initials: R
authors.lastname: Aantaa
mesh_terms: D000328:Adult; D000368:Aged; D000577:Amides / Q000008:administration & dosage*; D000775:Anesthesia, Spinal / Q000379:methods*; D019644:Arthroplasty, Replacement, Hip; D002045:Bupivacaine / Q000008:administration & dosage* / Q000031:analogs & derivatives; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D004334:Drug Administration Schedule; D005260:Female; D006801:Humans; D000077554:Levobupivacaine; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D000077212:Ropivacaine
chemical_list: D000577:Amides; D000077212:Ropivacaine; D000077554:Levobupivacaine; D002045:Bupivacaine