SERUM BUPIVACAINE CONCENTRATIONS DURING CONTINUOUS EXTRAPLEURAL INFUSION

Purpose: To determine the rate of increase in serum bupivacaine concen tration during continuous extrapleural infusion. Methods: After thorac otomy for lobectomy under general anaesthesia, nine patients had an ex trapleural catheter inserted, before chest closure, in a costovertebra l gutter constructed surgically by lifting the parietal pleura Bupivac aine 0.5% with epinephrine 1:200.000 was injected through the catheter as 0.3 ml.kg(-1) bolus followed by 0.1 ml.kg(-1).hr(-1) for five days . Serum bupivacaine (free and total), albumin, alpha-I acid glycoprote in concentrations were measured 15 min after injection and at 24 hr in tervals for five days. Bupivacaine concentrations were determined by c olumn liquid chromatography using solid phase extraction. Serum alpha- I acid glycoprotein concentration was determined by nephelometry on QM 300 protein analyzer. Serum albumin concentration was determined by b romocresol green dye binding procedure on Hitachi 717 Autoanalyzer.Res ults: A continuous elevation in total serum bupivacaine was observed, with an average value of 0.75 mu g.ml(-1) on day 1 to 2.77 mu g.ml(-1) on day 4 (P < 0.05); There was no increase in postoperative free seru m bupivacaine concentration; average value of 177 pcg.ml(-1) on day 1 and 249 pcg-ml(-1) on day 4 (P = 0.92). Postoperative serum alpha-I ac id glycoprotein concentration showed a steady nse with an average valu e of 0.94 mu g.ml(-1) on day 1 and 1.47 mu g.ml(-1) on day 4 (P < 0.05 ). No change was-observed in post-operative serum albumin with an aver age value of 31.4 g.l(-1) on day 1 and 31.3 g.l(-1) on day 4.Conclusio n: Continuous extrapleural infusion of bupivacaine over five days afte r thoracotomy is associated with a steady increase in total serum bupi vacaine concentration and no elevation in free serum bupivacaine conce ntration.