High plasma ropivacaine concentrations after fascia iliaca compartment block in children

Abstract

The pharmacokinetic profile of local anaesthetics is influenced by the mode of administration. We sought to compare the pharmacokinetics of two doses of ropivacaine after fascia iliaca compartment (FIC) block in children. In this prospective, double-blind study, children received an FIC block as a part of their anaesthetic management during elective orthopaedic surgery on the thigh. They were randomized to receive ropivacaine 0.7 ml x kg(-1) using either a 0.375% or 0.5% solution. Venous blood samples were drawn up to 6 h after injection. Plasma concentrations of ropivacaine were measured by gas-liquid chromatography. Six children (10.2 (range 5-15) yr, 35.6 (sd 10) kg were included. FIC block provided satisfactory peroperative pain relief. No signs of toxicity were observed, but high maximal plasma concentrations (C(max) 4.33-5.6 microg ml(-1)), were observed for three of four patients in the ropivacaine 0.5% group. The two patients in the 0.375% group showed values within the safe range (C(max) 0.66 and 0.98 microg ml(-1) respectively). Even though no toxic effects were observed, these results led us to discontinue the study. The administration of ropivacaine 3.5 mg x kg(-1) can be associated with sustained high plasma concentrations of ropivacaine, outside the tolerable range. In view of these results, we recommend the use of lower ropivacaine dosage during FIC block in children.