The effects of lidocaine on the whole body distribution of radioactively labeled microspheres in the conscious rat.

Radioactively labeled 15-micrometer microspheres were used to evaluate the effects of intravenous lidocaine on cardiac output and distribution of tissue blood flow in awake rats. After a one-hour control period, all animals (n = 22) received 85Sr-labeled microspheres for a control measurement. The animals were then divided into three groups. The control group (n = 6) received a bolus of saline and then an infusion of saline. After 40 minutes, a second microsphere (141Ce) was injected, the animals killed, and tissue blood flow determined. A second group of rats (n = 8) were similarly treated except that they received a bolus and infusion of lidocaine resulting in a plasma concentration of 1.98 +/- 0.3 microgram of lidocaine/ml. A third group of rats (n = 8) received a higher dose of lidocaine which resulted in a plasma concentration of 6.37 +/- 0.3 microgram of lidocaine/ml. In the control and low-dose lidocaine group, there were no changes in blood pressure, heart rate, cardiac output or tissue blood flow. At the higher lidocaine concentration, blood pressure remained the same but cardiac output and heart rate were decreased. Tissue blood flow to brain, heart and muscle was responsible for the increased peripheral resistance. These results suggest that high blood concentrations of lidocaine alter flow to vital organs in the rat.