Cardinal Health

Preventing Venous Thromboembolism: A Healthcare Professional Guide to Intervention 8 What Causes VTE. Causal Factors for Venous Thromboembolism. Nineteenth century German pathologist Rudolf Ludwig Karl Virchow established a three-pronged formula to explain the cause of thrombosis. This formula, commonly known today as Virchow’s Triad (see Figure 1. ), remains the prevailing theory of how DVT forms. DVT risk factors have their basis in at least one of the triad categories: 1. Stasis. Stasis is a primary causal factor associated with hospitalised patients. All hospital patients will be immobile for a period of time. Prolonged immobility will slow the circulation of blood and contributes to clot formation. There are additional patient related factors which also cause stasis, such as obesity, pregnancy and prior DVT. 2. Vessel Wall Damage. Vessel wall damage is thought to result from surgical limb manipulation producing vessel kinks intra-operatively in procedures such as knee or hip surgery. Pooling of venous blood following administration of smooth muscle relaxants and saline administered intra-operatively causes venous distension and consequently damages the endothelial lining of the vein walls. 3. Coagulation Changes. Coagulation factors are circulating blood proteins that are necessary for clot formation, dissolving old blood clots and preventing unwanted blood clots. Over 30 substances are involved with coagulation. The delicate balance between pro-coagulant (coagulant factors that promote clotting) and anti-coagulants (coagulation factors that prevent clotting) determines whether or not the blood will clot. A list of some coagulation factors are presented in Table 1 . Hyper-coagulability increases the risk of thrombus. This may result from deficiencies of factors in the blood that prevent clotting, increase in the factors that promote clotting or alterations in the viscosity and coagulation of blood itself. Table 1: Coagulation Factors Pro-coagulants Anti-coagulants Platelets Protein C Von willebrand factor Protein S Tissue factor Antithrombin Clotting factors I-XII Heparin cofactor II The Clotting Process. Coagulation and fibrinolysis are normal processes in the body. The coagulation cascade is a step by step process that results in the formation of a thrombus. Conversely, the fibrinolysis cascade outlines the process of thrombus breakdown. (see Figure 2. ) Vessel Wall Damage Coagulation Changes Stasis Virchow’s Triad Figure 1: Virchow’s Triad Coagulation Fibrinolysis Prothrombin Plasminogen Thrombin Plasmin Fibrinogen Fibrin Thrombus Fibrin Degradation Products (FDP) Increased Platelet Aggregation Figure 2: Coagulation & Fibrinolysis Cascade THE CLOTTING PROCESS: COAGULATION AND FIBRINOLYSIS ARE NORMAL PROCESSES IN THE BODY. THE COAGULATION CASCADE IS A STEP BY STEP PROCESS THAT RESULTS IN THE FORMATION OF A THROMBUS. CONVERSELY, THE FIBRINOLYSIS CASCADE OUTLINES THE PROCESS OF THROMBUS BREAKDOWN.