Smaller children have greater bupivacaine plasma concentrations after ilioinguinal block

Abstract

We have measured plasma concentrations of bupivacaine after ilioinguinal block in children of different sizes. We studied 14 children with weights 10-15 kg and 17 children with weights 15-30 kg. Each child received 0.5% bupivacaine 0.25 ml kg-1 (1.25 mg kg-1) (Carbostesin, Astra, Germany). Venous blood was obtained before the block (control) and at 5, 10, 15, 20, 30 and 60 min after block. Mean maximal concentration in the 10-15-kg group (1.5 (SD 0.9) mg litre-1, range 0.43-4.0 mg litre-1, at 18 (5) min) was significantly higher (P < 0.05) than that in the 15-30-kg group (0.9 (0.3) mg litre-1 range 0.35-1.34 mg litre-1, at 16 (5) min). In the 10-15-kg group, unexpectedly high (up to 4 mg litre-1) bupivacaine concentrations were observed and often concentrations remained high (> 2 mg litre-1) at 60 min. We conclude that smaller children appear to differ in the pharmacokinetic handling of bupivacaine. The maximum safe plasma concentration of bupivacaine in small children, although not clearly established, is likely to be approximately 4 mg litre-1. We recommend, therefore, that a dose of bupivacaine 1.25 mg kg-1 should not be exceeded in the perioperative period when performing ilioinguinal block in children < 15 kg in weight.