Prophylaxis Of Thromboembolic Disease

Preoperative management of the surgical patient includes planning to avoid fatal complication of pulmonary thrombo-embolism. Clinically significant but non-fatal thromboem-bolism occurs in about 1:100 postoperative patients and fatal pulmonary embolism in 1: 1000.

The origin of the pulmonary embolus is usually thrombosis in the veins of the calf muscles, but thrombosis may spread to the iliofemoral veins and the pelvic veins. The development of venous thrombosis in these veins is usually silent and may only manifest itself as an episode of pulmonary embolism. Hence the emphasis on prophylaxis to prevent this serious complication.

Many studies have defined a number of risk factors which predispose to the development of pulmonary embolism:

• immobilisation;

• general anaesthetic;

• major abdominal/orthopaedic surgery;

• pregnancy/postpartum;

• malignancy, particularly ovarian and pancreatic cancer;

• hypercoaguable states, for example, deficiency of antithrom-bin 3, protein C or protein S;

• medical illness, including myocardial ischaemia, respiratory insufficiency.

Surgical patients can be divided into low-, medium- and high-risk groups for venous thrombosis and pulmonary embolism. A typical low-risk patient will be:

• have surgery lasting <30 min, particularly avoiding general anaesthetic;

• rapidly mobilised postoperatively;

• have no other risk factors.

A typical moderate-risk patient will be:

• show moderate obesity;

• need abdominal operation requiring general anaesthetic;

• have one other risk factor.

A typical high-risk patient will be:

• middle-aged or elderly, undergoing major surgery (orthopaedic or cancer surgery);

• need prolonged mobilisation;

• may have pelvic trauma or pelvic surgery;

• may have suffered orthopaedic trauma generally: for example, fractured neck of femur;

• have multiple risk factors.

All moderate- to high-risk patients should receive prophylaxis. It is not easy to categorise every patient and when in doubt prophylaxis against thromboembolism should be instituted.

Methods of prophylaxis

General

• early ambulation;

• use of venous support compression stockings, particularly where local venous insufficiency problems exist in the limbs;

• calf stimulation during operations under general anaesthetic.

These methods are sufficient prophylaxis for fit patients who fall in the low-risk group.

Moderate and high-risk patients

These patients require pharmacological intervention with antithrombotic drugs.

• Low-dose subcutaneous heparin. This has been shown to be effective in reducing thrombosis in the peripheral veins. It is given at a dose of 5000 units bd subcutaneously. The main complications are bruising and local wound haematoma if the injection is given close to the site of the operative wound. The heparin at this dose does not produce any alteration in standard coagulation screening studies. The main complication is the development of allergic thrombocytopaenia. This condition may be associated with thrombosis and heparin must be ceased.

• Low-molecular-weight heparin (LMWH). This may have a special place in orthopaedic surgery and is given as a single daily dose. It is as effective as heparin in preventing thrombosis and has fewer platelet side-effects. However, LMWH is expensive and is not routinely used for this reason.

• Anticoagulants. Use of the anticoagulant warfarin, either in low or full anticoagulation dose, has been shown to be effective in reducing thromboembolism. However, bleeding complications are common and accordingly warfarin is not in regular use for this purpose.

• Antiplatelet agents. Aspirin is an effective antiplatelet agent. However, it is ineffective as the sole agent to prevent DVT. Dextrans act as antiplatelet agents and have been shown to reduce the incidence of postoperative venous thrombosis. They are, however, expensive, must be given intra-venously and are more difficult to administer than subcutaneous heparin. Dextrans are not used routinely.

Post operative care

Part of the postoperative management of the surgical patient is to check the limbs on a daily basis for the development of the early signs of venous thrombosis. These include calf tenderness and leg swelling. If there is any suggestion of the development of clinical venous thrombosis, a Doppler ultrasound and/or venogram is required to diagnose the peripheral venous thrombosis prior to the commencement of full anticoagulation.

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