title: The ED50 and ED95 of intrathecal isobaric bupivacaine with opioids for cesarean delivery.
abstract: BACKGROUND
  The ideal intrathecal isobaric bupivacaine dose for cesarean delivery anesthesia is uncertain. While small doses (5-9 mg) of bupivacaine may reduce side effects such as hypotension, they potentially increase spinal anesthetic failures. This study determined the ED50 and ED95 of intrathecal isobaric bupivacaine (with adjuvant opioids) for cesarean delivery.
  
  
  METHODS
  After institutional review board approval and written informed consent were obtained, 48 parturients undergoing elective cesarean delivery under combined spinal-epidural anesthesia were enrolled in this double-blind, randomized, dose-ranging study. Patients received a 5-, 6-, 7-, 8-, 9-, 10-, 11-, or 12-mg intrathecal isobaric bupivacaine dose with 10 microg fentanyl and 200 microg morphine. Overall anesthetic success was recorded when no intraoperative epidural supplement was required during the cesarean delivery. ED50 and ED95 values for overall anesthetic success were determined using a logistic regression model.
  
  
  RESULTS
  ED50 and ED95 values for overall anesthetic success were 7.25 and 13.0 mg, respectively. No advantages for low doses could be demonstrated with regard to hypotension, nausea, vomiting, pruritus, or maternal satisfaction, although this study was underpowered to detect significant differences in secondary outcome variables.
  
  
  CONCLUSIONS
  The ED50 and ED95 values (7.25 and 13.0 mg, respectively) for intrathecal isobaric bupivacaine in this circumstance are similar to values the authors determined recently for hyperbaric bupivacaine using similar methodology. These ED50 and ED95 values are significantly higher than those advocated in previous reports in which success was claimed using lower intrathecal bupivacaine doses. The current study used stricter criteria to define "successful" anesthesia and support the use of larger bupivacaine doses to ensure adequate patient comfort.
authors.affiliation: Department of Anesthesia, Stanford University School of Medicine, California 94305, USA. bcarvalho@stanford.edu
authors.forename: Brendan
authors.initials: B
authors.lastname: Carvalho
authors.forename: Marie
authors.initials: M
authors.lastname: Durbin
authors.forename: David R
authors.initials: DR
authors.lastname: Drover
authors.forename: Sheila E
authors.initials: SE
authors.lastname: Cohen
authors.forename: Yehuda
authors.initials: Y
authors.lastname: Ginosar
authors.forename: Edward T
authors.initials: ET
authors.lastname: Riley
mesh_terms: D000328:Adult; D000773:Anesthesia, Obstetrical; D002045:Bupivacaine / Q000008:administration & dosage* / Q000009:adverse effects; D002585:Cesarean Section; D004311:Double-Blind Method; D005260:Female; D005283:Fentanyl / Q000008:administration & dosage*; D006801:Humans; D007278:Injections, Spinal; D016015:Logistic Models; D009020:Morphine / Q000008:administration & dosage*; D011247:Pregnancy; D011446:Prospective Studies
chemical_list: D009020:Morphine; D005283:Fentanyl; D002045:Bupivacaine