Effect of plasma alpha(1)-acid glycoprotein concentration on the accumulation of lidocaine metabolites during continuous epidural anesthesia in infants and children

Objective: alpha(1)-acid glycoprotein (AAG) is an acute-phase protein that is responsible for binding basic drugs such as lidocaine (LDC). The effect of AAG on the duration of LDC during continuous epidural anesthesia in infa nts and young children was investigated. Patients, materials and methods: P lasma levels of LDC and its active metabolites, monoethylglycinexylidide (M EGX) and glycinexylidide (GX), were monitored in 20 infants and children, 5 months to 6 years of age, who received continuous epidural infusion of 2.5 mg kg(-1) LDC hourly during abdominal or thoracic surgeries. Results: Plas ma LDC concentrations were constant after the first hour of injection. In c ontrast, the concentrations of MEGX and GX increased continuously during ep idural infusion in all patients. The plasma AAG concentration correlated si gnificantly (r = 0.814, p < 0.001) with the steady-state LDC level. In addi tion, significant inverse correlation was observed between the plasma AAG c oncentration and the accumulation rate of MEGX (r = 0.742, p = 0.002). The plasma AAG concentration and the accumulation rate of GX correlated weakly (r = 0.474, p = 0.035). There was no correlation between the age of the pat ient and the plasma AAG concentrations (r = 0.295, p = 0.206). Conclusion: Our results suggest that the plasma AAG concentration is a valuable index i n preventing the toxicity caused by accumulation of MEGX during continuous epidural anesthesia of LDC.