[Plasma determination of lidocaine and bupivacaine after caudal anesthesia in children].

Serum concentrations of lidocaine and plasma concentrations of bupivacaine were measured so as to assess the risk of systemic toxicity following their administration by the caudal route in children, and study their pharmacokinetic profiles according to age. The serum concentrations of lidocaine were measured by immuno-enzymology in 37 children (23 +/- 13 kg) during the first hour after administration of 7 mg . kg-1. The plasma concentrations of bupivacaine were measured by high performance liquid chromatography in 40 children (18.03 +/- 8.90 kg) during the first hour after administration of 2.5 mg . kg-1. The greatest concentrations observed between 15 and 30 min after the injection were of 2.40 +/- 0.86 micrograms . ml for lidocaine and 0.93 +/- 0.44 microgram . ml-1 for bupivacaine. Higher values were observed in infants weighing less than 12 kg where they reached 2.89 +/- 0.72 and 1.52 +/- 0.68 micrograms . ml-1 respectively. These results showed that caudal anaesthesia with lidocaine (7 ml . kg-1) and bupivacaine (2.5 ml . kg-1) was a safe technique for children, giving average plasma concentrations inferior to toxic values. However, it seemed prudent not to give more than the prescribed doses in the small infant.