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The Pathophysiology of VTE

Venous thrombus formation and propagation most usually depend on the presence of one or more of the following:

  • venous stasis
  • blood vessel wall trauma or abnormality
  • increased risk of blood coagulation

These elements are known collectively as Virchow’s triad (Figure. 1) and many predisposing factors can alter one or more of these factors.

Figure 1: ViRchow's Triad

Venous Stasis
Venous stasis occurs when there’s a decrease in movement of blood, causing venous congestion in the lower extremities; this may occur after prolonged immobility or confinement to bed. Venous obstruction can also arise from external compression by enlarged lymph nodes, tumours or intravascular compression by previous thromboses 1.

Vein injury
The endothelium (lining) of a healthy vein is smooth and provides a physical barrier between the circulating blood and the thrombogenic tissues beneath. When the vein becomes injured the lining loses its normal negative charge, becoming rough and provoking platelet aggregation and adhesion. Endothelial injury may be caused by a previous DVT, venous distension, trauma and surgery.

Hypercoagulability
Changes in blood chemistry causing hypercoagulability (increased blood stickiness) can occur as a result of many factors including dehydration, malignancy, surgery or trauma, oestrogen therapy and systemic inflammatory diseases.

The risk of VTE by clinical speciality
Geerts et al (2008) representing the American College of Chest Physicians (ACCP) identified the frequency of DVT in hospitalised patients in the absence of prophylaxis 2.

Patient Group Prevalence without prophylaxis
Medical patients 10-20%
General surgery 15-40%
Major gynaecological surgery 15-40%
Major urologic 15-40%
Neurosurgery 15-40%
Stroke 20-50%
Hip / knee arthroplasty 40-60%
Major trauma 40-80%
Spinal cord injury 60-80%
Critical care patients 10-80%

 

 

Table 1: VTE incidence rates without prophylaxis


Table 1 illustrates the high incidence of DVT and thus the requirement for effective prophylactic measures.

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1  Turpie AG, Chin BS, Lip GY. Venous thromboembolism: pathophysiology, clinical features and prevention. BMJ. 2002; 325: 887-890.

2 Geerts WH, Bergqvist D, Pineo GF et al. Prevention of venous thromboembolism. Chest. 2008; 133 (6): 381S-453S.

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