Interrelationships of hepatic blood flow, cardiac output, and blood levels of lidocaine in man

Factors that regulate the arterial level of lidocaine during a constant infusion were investigated in 17 patients undergoing cardiac catheterization. Lidocaine was administered by a 50 mg bolus, followed by a constant infusion of 40 µg/kg/min until steady state conditions were achieved. Cardiac output and estimated hepatic blood flow were also determined. An inverse relationship between arterial lidocaine levels and cardiac index was observed. With a low cardiac index of 1.9 ± 0.3 liters/min/m 2 the arterial level was 2.4 (±0.4 sem ) µg/ml, while with a normal cardiac index of 3.3 ± 0.8 liters/min/m 2 it was 1.5 (±0.2 sem ) µ/ml. A linear relationship was also observed between estimated hepatic blood flow and cardiac index. Therefore, an inverse relationship between arterial lidocaine levels and estimated hepatic blood flow was noted. At steady-state conditions, the liver accounted for 70% (±16% sem ) of the metabolism or removal of the lidocaine administered. These studies suggest that the administration of smaller doses of lidocaine will produce effective therapeutic levels when reduced hepatic blood flow exists.