Direct and Indirect Effect of Some Local Anesthetics on Muscle Blood Flow—Tissue Oxygen Pressure

Lidocaine (or mepivacaine) was infused in rabbits first in the lower part of the aorta to provoke a direct effect on thigh skeletal muscle blood flow and later intravenously to produce a generalized circulatory effect. The effect on thigh muscle blood flow was evaluated by measurements of muscle surface oxygen tension (p t O 2 ) with the help of the MDO electrode. Both mean values and types of histograms were studied. Our study shows that both local anesthetic agents tested produced a decreased skeletal muscle blood flow because of a vasocon-striction, when given into the aorta (most likely due to a direct stimulatory effect on the smooth muscles in peripheral vessels). In contrast, an intravenous infusion provoked an increased blood flow that indicated a vasodilation, an effect that could be explained by an increase in cardiac output and a decrease in systemic vascular resistance. Thus, the general circulatory effect of a local anesthetic seems to override a direct vasoconstrictor effect on the peripheral vessels.