Arterial thrombosis

This occurs in relation to damaged endothelium, e.g. atherosclerotic plaques. Exposed collagen and released tissue factor cause platelet aggregation and fibrin formation (Box 44.1).

Venous thrombosis

All hospital in-patients are assessed for risk of venous thromboembolism (VTE) and appropriate measures for VTE prophylaxis instituted where indicated. The most common site for deep vein thrombosis (DVT) is the leg which may be below knee or involve veins in the thigh and the iliac veins.

Factors affecting blood flow (e.g. stasis, obesity), alterations in blood constituents and damage to vascular endothelium (e.g. caused by sepsis, surgery or indwelling catheters) are important risk factors (Box 44.2). Diagnosis can be confirmed by imaging, e.g. Doppler ultrasound probe (Fig. 44.1) or, less commonly, venography. Blood tests, e.g. detection of elevated levels of d-dimers, which are derived from fibrinogen, can also be helpful, especially if recurrence is suspected.

Box 44.2 Risk factors for venous thrombosis

Conditions causing stasis

Cardiac failure, oedema, nephrotic syndrome

Postoperative

Immobility and bed rest

Trauma

Pelvic obstruction

Altered blood constituents

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