Serum bupivacaine concentrations during continuous extrapleural infusion

PurposeTo determine the rate of increase in serum bupivacaine concentration during continuous extrapleural infusion.MethodsAfter thoracotomy for lobectomy under general anaesthesia, nine patients had an extrapleural catheter inserted, before chest closure, in a costovertebral gutter constructed surgically by lifting the panetal pleura. Bupivacaine 0.5% with epinephnne 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-1 acid glycoprotein concentrations were measured 15 min after injection and at 24 hr intervals for five days. Bupivacaine concentrations were determined by column liquid chromatography using solid phase extraction. Serum alpha-1 acid glycoprotem concentration was determined by nephelometry on QM 300 protein analyzer. Serum albumin concentration was determined by bromocresol green dye binding procedure on Hitachi 717 Autoanalyzer.ResultsA continuous elevation in total serum bupivacaine was observed, with an average value of 0.75 μg· ml on day 1 to 2.77 μg· ml on day 4 (P< 0.05). There was no increase in postoperative free serum bupivacaine concentration; average value of 177 pcg· ml−1 on day 1 and 249 pcgml−1 on day 4 (P=0.92). Postoperative serum alpha-1 acid glycoprotein concentration showed a steady rise with an average value of 0.94 μg· ml−1 on day 1 and 1.47 μg·ml−1 on day 4 (P< 0.05). No change was observed in post-operative serum albumin with an average value of 31.4 g· l−1 on day 1 and 31.3 g· l−1 on day 4.ConclusionContinuous extrapleural infusion of bupivacaine over five days after thoracotomy is associated with a steady increase in total serum bupivacaine concentration and no elevation in free serum bupivacaine concentration.