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[Hematologic changes induced by extracorporeal circulation].

The plasma and cellular changes seen during the use of extracorporeal circulatory circuits define the system's degree of haemocompatibility. Heparin is still very much used to prevent activation of the blood clotting mechanisms and to reduce their effects. The fall in concentration of the clotting factors and their inhibitors is usually moderate; it is due to haemodilution, particularly important in cardiac surgery and during plasma exchanges. Fibrinolysis is often activated. In cardiac surgery, it is seen in nearly 20% of cases straight after the end of the ECC, and in nearly 80% of cases during the ECC. In all cases of resin haemoperfusion, there is an early transitory fibrinolytic burst, seen only rarely during haemodialysis and plasma exchanges. This phenomenon is usually well controlled by the natural inhibitors; it can be prevented by antifibrinolytic drugs. Cellular changes show the same trends during cardiac surgery, haemoperfusion and haemodialysis. Thrombopaenia is seen within a few minutes starting of ECC. It is caused by platelet activation, with aggregate formation; these are then trapped by the microcirculation. Leukopaenia occurs at the same time, later followed by rebound; complement activation could be the main cause by forming aggregates of polymorphonuclear cells and monocytes. Intravascular mechanical haemolysis reaches significant levels only in a few cardiac surgical procedures. The great speed of activation of the plasma and platelet enzyme systems by the ECC circuits explains these early changes. They are not only due to direct effects of the physiological circulatory characteristics and to contact with artificial surfaces, but also to plasma-cell interactions and to the patients' reaction to these first alterations.