Plasma concentrations of bupivacaine after lumbar sympathetic block.

To determine the pharmacokinetics of local anesthetics after lumbar sympathetic blocks, total and free (unbound) plasma concentrations of bupivacaine in venous blood samples were measured in 12 patients using a high-performance liquid chromatography (HPLC) technique. Administration of 30 mL of plain bupivacaine 0.175%, via two needles, resulted in a maximum total plasma concentration of 0.2-1.0 mg/L (mean 0.49 mg/L). These maximum concentrations were reached 10-45 min after the injection (mean 24 min). There were no clinical signs of central nervous system (CNS) toxicity attributable to local anesthetics. All patients showed hemodynamic stability after the blocks. We conclude that the absorption of local anesthetics after lumbar sympathetic blocks is slow compared to stellate ganglion or intercostal blocks, and does not result in toxic plasma concentrations. These blocks might well be performed in outpatients.