ABSTRACT
This study was performed to assess the concentrations of plasma lidocaine and its major metabolite [monoethylglycinexylidide [MEGX]] in children receiving continuous thoracic epidural anesthesia after oral clonidine premedication. Ten pediatric patients, aged 1-9 years, were randomly allocated to the control or clonidine 4 mug/kg group [n = 5 each]. Anesthesia was induced and maintained with sevoflurane in oxygen and air [F1O2 40%] epidural puncture and tubing was carefully performed at the thoracic 11-12 intervertebral space. An initial dose of 1% lidocaine [5 mg/kg] was injected through a catheter in the epidural space, followed by 2.5 mg/kg/hr. The plasma concentrations of lidocaine and MEGX were measured at 15 minutes, 30 minutes and every 60 minutes for 4 hours after the initiation of continuous epidural injection. The concentrations of lidocaine and MEGX were measured using high-pressure liquid chromatography with ultraviolet detection. The hemodynamic variables were similar between the control and clonidine groups during anesthesia. The clonidine group showed significantly smaller lidocaine concentrations and the concentration of MEGX tended to be smaller in the plasma of the clonidine group for the initial four hours after the initiation of epidural infusion. In conclusion, oral clonidine pre-anesthetic medication at a dose of 4 mug/kg decreases plasma lidocaine concentration in children