[Mechanism of action of intravenous regional anesthesia]

It is considered that the anesthetic solution administered according to the regional intravenous anesthesia method will be non-uniformly dispersed due to the valvular system of the veins, the competence and disposition of which varies from one individual to the other. The anesthetic solution will progress to the level of venous capillaries, but will penetrate the tissues of the blood-deprived segment in variable concentrations. The anesthetic will pass from the venous network to the extravascular space in large amounts and this is facilitated by the vasodilatation, increased vascular permeability, and the increased number of functional capillaries. The anesthetic drug when present at the level of the cells will exert its action on the cellular membrane by a process which is facilitated by low pH and hypercapnia decreasing excitability and conduction in the nerves. The anesthetic solution will exert its action both at the level of the trunk and at the level of the peripheral nerve endings. However, the major effects occur at the periphery, while trunk blockade is secondary and mostly due to consecutive ischaemic modifications.