title: Isobaric bupivacaine via spinal catheter for hip replacement surgery: ED50 and ED95 dose determination.
abstract: BACKGROUND
  Continuous spinal anaesthesia with spinal catheters allows incremental dosing of the local anaesthetic and, consequently, less haemodynamic change. However, little is known about the required doses. Therefore, we designed a study to assess the local anaesthetic doses of isobaric bupivacaine which were effective in 50% (ED50) and 95% (ED95) of patients undergoing hip replacement surgery.
  
  
  METHODS
  Forty-eight patients undergoing hip replacement surgery were randomly allocated to one of six possible groups of eight patients to receive 6, 7, 8, 9, 10 or 12 mg of isobaric bupivacaine in a double-blind manner. The ED50 and ED95 values were calculated by a logistic regression model. The position of the spinal catheter tip was confirmed by X-rays.
  
  
  RESULTS
  The ED50 and ED95 values were 7.1 mg (95% confidence interval, 6.0-8.4) and 12.3 mg (95% confidence interval, 8.9-15.7), respectively. The location of the tip of the intrathecal catheter had no effect on local anaesthetic requirements. Eight patients required ephedrine after anaesthesia induction and a further 11 patients required ephedrine for correction of hypotension during surgery.
  
  
  CONCLUSIONS
  The observed ED50 and ED95 values may guide us to use small doses of isobaric bupivacaine for hip replacement surgery. Hypotension is still possible even if low doses of isobaric bupivacaine are used.
authors.affiliation: Department of Anaesthesia and Intensive Care, Tartu University Clinics, Tartu, Estonia. andres.sell@klinikum.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; D000775:Anesthesia, Spinal / Q000295:instrumentation* / Q000379:methods*; D000779:Anesthetics, Local / Q000008:administration & dosage / Q000627:therapeutic use*; D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D002045:Bupivacaine / Q000008:administration & dosage / Q000627:therapeutic use*; D002404:Catheterization / Q000295:instrumentation; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D004809:Ephedrine / Q000008:administration & dosage; D005260:Female; D006801:Humans; D007022:Hypotension / Q000188:drug therapy; D008297:Male; D008875:Middle Aged; D014662:Vasoconstrictor Agents / Q000008:administration & dosage
chemical_list: D000779:Anesthetics, Local; D014662:Vasoconstrictor Agents; D004809:Ephedrine; D002045:Bupivacaine