title: Determining minimum effective anesthetic concentration of hyperbaric bupivacaine for spinal anesthesia.
abstract: We determined the minimum effective anesthetic concentration (MEAC) of bupivacaine for spinal anesthesia, defined as the median effective concentration at which a spinal anesthetic produces surgically equivalent anesthesia within 20 min of administration in 50% of human subjects. Two doses of spinal bupivacaine (7.5 mg and 10 mg) were administered to 45 volunteers (19-39 yr) in a randomized, double-blinded fashion. Hyperbaric bupivacaine solutions of 0.1% to 0.75% containing 8.25% dextrose were administered intrathecally and MEAC established by using the Dixon's up-and-down method. Complete anesthesia was defined as: 1) pinprick anesthesia at or higher than T12; 2) anesthesia to transcutaneous tetanic electric stimulation (50 Hz at 60 mA for 5 s) in the knees; and 3) complete leg paralysis, all occurring in both lower extremities within 20 min of intrathecal injection. We found that the MEAC of spinal bupivacaine was 0.43% (95% confidence interval 0.24-0.62) when 10 mg was administered. At this dose, a concentration as low as 0.1% could provide complete anesthesia, but consistent blockade was obtained only with the 0.7% solution. The 7.5-mg dose failed to provide complete anesthesia consistently, even in the presence of 0.75% (maximum). The current commercially available 0.75% concentration of hyperbaric bupivacaine seems to be clinically optimal when 10 mg is used if complete bilateral lower extremity blockade is desired.
authors.affiliation: Department of Anesthesia, University of Toronto, The Toronto Western Hospital, University Health Network, Toronto, Ontario, Canada.
authors.forename: V W
authors.initials: VW
authors.lastname: Chan
authors.forename: P
authors.initials: P
authors.lastname: Peng
authors.forename: H
authors.initials: H
authors.lastname: Chinyanga
authors.forename: S
authors.initials: S
authors.lastname: Lazarou
authors.forename: J
authors.initials: J
authors.lastname: Weinbren
authors.forename: Z
authors.initials: Z
authors.lastname: Kaszas
mesh_terms: D000328:Adult; D000775:Anesthesia, Spinal; D000779:Anesthetics, Local / Q000008:administration & dosage*; D002045:Bupivacaine / Q000008:administration & dosage*; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D008297:Male; D011446:Prospective Studies; D012677:Sensation
chemical_list: D000779:Anesthetics, Local; D002045:Bupivacaine