methods of maintaining, with special apparatus, the circulation of blood and metabolism in the body or individual parts and organs of the body at an optimum level by perfusion (passage of blood or liquid blood substitute).

Different methods of extracorporeal circulation are used, depending on the indications. General perfusion involves total exclusion of the heart and lungs from the blood circulation and their temporary replacement by a special device; it is used in certain operations on the heart and large blood vessels. Auxiliary perfusion is used when it is necessary to temporarily ease the functioning of the heart and lungs by mechanical means—for example, in cardiac and pulmonary insufficiency or in resuscitating an individual pronounced clinically dead. Regional or isolated perfusion, whereby only part of the body or individual organs temporarily deprived of the normal inflow of blood are perfused mechanically, is performed in the treatment of certain diseases and injuries (endarteritis obliterans and certain malignant tumors, for example). When tumors are treated, massive doses of cytostatic substances (agents that suppress cell multiplication) are added to the liquid perfused. Regional perfusion calls for having the heart and lungs simultaneously provide adequate circulation for the rest of the body. Regional perfusion is also used to preserve organs slated for transplantation.

The effectiveness of extracorporeal circulation depends on how well it is carried out—that is, maintenance during perfusion of the volume of the perfusion current, arterial and venous pres-sure, volume of circulating blood, monitoring and correction of metabolic processes (acid-base equilibrium, water-electrolyte balance, blood gases), brain activity, kidney function, biochemical parameters, and cellular composition of the peripheral blood. For this purpose the patient receives transfusions of blood and blood preparations, alkaline solutions, electrolytes, diuretics, and so forth during and after extracorporeal circulation. The effectiveness of extracorporeal circulation is increased by combining it with general or local hypothermia, which greatly reduces oxygen consumption by the tissues, thereby permitting the rate of perfusion to be slowed.

The first operations on the human heart using extracorporeal circulation were performed by the Americans F. D. Dodrill (1952) and J. H. Gibbon (1954) and by the Soviet surgeon A. A. Vishnevskii (1957). The principle of extracorporeal circulation underlies the functioning of the artificial kidney.