[Continuous block of the femoral nerve after surgery of the knee: pharmacokinetics of bupivacaine]

Abstract

Ten ASA Class 1 and 2 patients, aged from 16 to 56 years (mean +/- SD: 37 +/- 17 years), scheduled for knee surgery were studied. At the end of the surgical procedure under general anesthesia, an epidural catheter was inserted in the femoral space. After X-ray opacification, a bolus of 2.5 mg.kg-1 of 0.5% bupivacaine with epinephrine was injected. A maintenance infusion was performed during 48 hours with 0.25 mg.kg-1.h-1 of 0.125% bupivacaine without epinephrine. Pain score recorded with an visual analogue scale was 5.0 +/- 1.9 before femoral block. Pain score decreased significantly from 6 to 48 hours. Plasma bupivacaine levels at 24, 36 and 48 hours were significantly higher than the levels obtained at 30 min, 1, 6 and 12 hours. Mean plasma bupivacaine level at steady state was 1.78 +/- 0.59 micrograms.ml-1. Clearance of bupivacaine was 2.59 +/- 0.91 ml.min-1.kg-1. No neurologic complications have been recorded.