Microcirculatory actions of general anesthetics

General anesthesia, either with the inhalation or the nonvolatile anesthetics, results in significant changes in the microvasculature. The anesthetics alter microvascular diameters in the resting animal and they change the responses to stress (i.e., catecholamine stimulation or hemorrhage) also. Alterations in the microvasculature involve primarily changes in the diameters of arterioles and venules and these, combined with the associated changes in arterial pressure and cardiac output, are responsible for the changes in organ blood flow that occur during general anesthesia. General anesthetics alter the in vivo vascular smooth muscle responses to topically applied vasoactive substances such as epinephrine or norepinephrine. The microvascular responses to hemorrhage are altered by the anesthetics and the changes are most pronounced in the smaller (approximately 20 micrometers) arterioles. Anesthetic influences on the microcirculation are unique for each agent and are not the result of the general state of narcosis. Anesthetic influences on the microvasculature are both dose-dependent and tissue-specitic. The peripheral vascular effects of the anesthetics may influence the choice of anesthesia and may alter the results of experimental investigations performed in anesthetized animals.