Disorders of venous blood flow during surgery and the postoperative period as a pathomechanism of venous thrombosis of the legs

Abstract An increased risk of thrombosis is given in slowed movement of blood, damaged vascular wall as well as changed blood composition. The frequency of venous thrombi during and after operative interventions speaks in favour of the importance of the reduced venous return to the heart. In the operative phase the reversible negative inotropic effect of numerous anaesthetics causes a blood stasis with an increase of the filling pressure of the heart (preload) and a reduction of the effect of the Frank-Starling mechanism. While the spontaneous respiration promotes the physiological venous return to the heart, this blood flow is partly inhibited by positive pressure breathing and during opening of the thoracic cage. Also changes of the blood volume have an influence on the venous return to the heart. Additional influences are the reduced muscle tone due to anaesthetics and to muscle relaxants as well as as mechanical injury of the skeletal muscles which led to a retarded blood flow. Apart from these factors in the postoperative phase are additionally present chronic stasis appearances in front of the right heart as well as a reduction of the sensitivity of atrial receptors in the insufficient heart. Also the therapeutic use of vasoactive substances as well as the presence of a varicosis influence the flow rate in the veins. An increased risk for thrombosis also exists after bed confinement because of atrophic changes of the skeletal and vascular muscles.(ABSTRACT TRUNCATED AT 250 WORDS)