Epinephrine does not reduce the plasma concentration of lidocaine during continuous epidural infusion in children

During continuous epidural anesthesia with lidocaine, plasma monoethylglycinexylidide (MEGX), an active metabolite of lidocaine, increases continuously. We assessed the effect of epinephrine on the absorption of lidocaine and the accumulation of MEGX during continuous epidural anesthesia in children.

Anesthesia was administered as an initial bolus of 5 mg x kg(-1) of 1% lidocaine solution followed by continuous infusion at 2.5 mg x kg(-1) x hr(-1). Patients in the control group (n = 8) received lidocaine alone, while patients in the epinephrine group (n = 8) received lidocaine + epinephrine (5 microg x mL(-1)). Concentrations of lidocaine and its active metabolite, MEGX, were measured in plasma samples obtained after 15 min, 30 min, and one, two, three, four, and five hours of infusion using high-performance liquid chromatography with ultraviolet detection.

Plasma lidocaine concentrations were higher in samples from the control group for the first hour; however, after two hours the levels were the same in all samples. Plasma MEGX levels increased continuously in both groups and were significantly higher in the control group samples. The sum of lidocaine + MEGX was higher in the control group for the first two hours but there was no significant difference between groups after three hours.

Reduction of the potential for systemic toxicity by the addition of epinephrine to lidocaine is limited, because the reduction of the sum of the plasma concentrations of lidocaine and its active metabolite MEGX is small and limited to the initial phase of infusion.