Smaller children have greater bupivacaine plasma concentrations after ilioinguinal block

We have measured plasma concentrations of bupivacaine after ilioinguinalblock in children of different sizes. We studied 14 children with weights10-15 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) wassignificantly 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 the10-15-kg group, unexpectedly high (up to 4 mg litre-1) bupivacaineconcentrations were observed and often concentrations remained high (> 2mg litre-1) at 60 min. We conclude that smaller children appear to differin the pharmacokinetic handling of bupivacaine. The maximum safe plasmaconcentration of bupivacaine in small children, although not clearlyestablished, 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 exceededin the perioperative period when performing ilioinguinal block in children< 15 kg in weight.