title: Plasma concentrations of bupivacaine and two of its metabolites during continuous interscalene brachial plexus block.
abstract: An interscalene brachial plexus block was performed via a catheter with 20-28 ml of 0.75% bupivacaine plus adrenaline for surgery of the shoulder region in 12 patients. Constant infusion of 0.25% bupivacaine 0.25 mg kg-1 h-1 was continued for 24 h. During surgery light general anaesthesia, without analgesics, was maintained. Plasma concentrations of total and unbound (free fraction) bupivacaine, desbutylbupivacaine (DBB), 4-hydroxybupivacaine (4-OHB) and alpha 1-acid glycoprotein (AAG) were measured at predetermined intervals during the continuous block. The greatest mean plasma concentrations of bupivacaine were measured at 30 min (1.63 (SD 0.55) micrograms ml-1) and 60 min (1.38 (0.48) micrograms ml-1). There was a small but statistically significant increase in the plasma concentration of bupivacaine between 12 and 24 h of infusion. The mean unbound concentration of bupivacaine in plasma decreased from 0.044 (0.015) microgram ml-1 (3.6 (1.1)% of total bupivacaine concentration) at 3 h to 0.023 (0.011) micrograms ml-1 (2.1 (1.0)%) at 24 h. The AAG concentration in plasma increased by 38% in 24 h. The metabolites DBB and 4-OHB were detectable in plasma from 30 min, with a gradual increase during infusion. At 24 h the mean concentrations of DBB and 4-OHB were 0.33 (0.22) micrograms ml-1 and 0.13 (0.04) micrograms ml-1, respectively. There were no toxic reactions during the blocks.
authors.affiliation: Department of Anaesthesiology, Surgical Hospital, Helsinki University Central Hospital, Finland.
authors.forename: P H
authors.initials: PH
authors.lastname: Rosenberg
authors.forename: P
authors.initials: P
authors.lastname: Pere
authors.forename: R
authors.initials: R
authors.lastname: Hekali
authors.forename: M
authors.initials: M
authors.lastname: Tuominen
mesh_terms: D000328:Adult; D000368:Aged; D001711:Biotransformation; D001917:Brachial Plexus; D002045:Bupivacaine / Q000031:analogs & derivatives* / Q000097:blood* / Q000378:metabolism / Q000493:pharmacokinetics; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009407:Nerve Block; D009961:Orosomucoid / Q000378:metabolism; D010149:Postoperative Pain / Q000517:prevention & control; D013997:Time Factors
chemical_list: D009961:Orosomucoid; C051879:4'-hydroxybupivacaine; C025149:2',6'-pipecoloxylidide; D002045:Bupivacaine