Deep Venous Thrombosis
by Dr Panayiotopoulos, Consultant Vascular and General Surgeon Essex.

Venous thrombosis is the presence of clot, more or less extensive, in the venous return circulation. It can affect either the superficial veins [superficial thrombophlebitis] or the deep veins that run between the muscles and convey almost all of the blood towards the heart [Deep Venous Thrombosis, DVT].

It often occurs after a surgical operation, prolonged bed rest, blood hypercoagulability or pressure on the deep veins, but it can also occur out of the blue.

2. What causes DVT?

Venous thrombi are initiated by changes in the coagulation mechanisms of the blood, damage to the endothelial lining of the vessels and by slowing or reduction of the blood flow [the most important]; these 3 conditions were described 150 years ago [in 1854] by Virchow; only recently a fourth factor was added, derangements of the fibrinolytic state [mechanism to dissolve the clot] of the patient.

Certain factors change the balance of these mechanisms.

·        “Endothelial damage” often pre-exists following an injury, childbirth, surgical operation, trauma, or previous thrombosis that has caused venous scarring.

·        “Slowing of blood flow” occurs in chronic venous insufficiency, prolonged bed rest, immobility, recovery from surgery.

·        “Hypercoagulability” can be congenital [because of deficiencies in blood and tissue factors including antithrombin III, protein C, protein S and plasminogen activator, the latter being vital for dissolving the clot] or be temporarily caused by trauma, surgery, illness [i.e. presence of malignancy] or specific drugs.

Many patients will have more than one risk factors; the risk is greatly increased by the presence of two or more factors. Surgery interferes with all three factors mentioned above, however, the risk varies, depending on the severity, the extent and duration of the operation and the type and site of procedure.

3. How common is DVT and what can it cause to me?

It is difficult to assess the incidence of DVT accurately, as in many cases it may exist without clinical symptoms. Using objective diagnostic techniques, DVT [symptomatic or silent] is detectable in 20-35% of patients after major operations and 20-50% to patients after myocardial infarction or stroke. However, even silent DVTs can cause the three serious complications which are:

·        Pulmonary embolism. It kills 1/10000 men and 1/6000 women every year in England. Occurs when the clot is detached from the deep vein and is lodged in the heart vessels that bring blood to the lungs. Although small emboli are far more common and do not cause serious problems, massive embolism can stop blood oxygenation in the lungs and lead to heart failure and circulatory collapse.

·        Chronic venous insufficiency [high venous pressure causing swelling of the limb and changes in the skin with brown pigmentation, eczema, lipodermatosclerosis and finally ulceration] is caused by DVT or immobilization/sedentary life style, but may appear many years after the acute thrombosis, from chronic venous scarring and venous stasis. It is difficult to assess the percentage of DVTs that end up with chronic venous insufficiency, but it is estimated to be around 6%.
 

·        Leg ulcer. About 2% of people will be affected by leg ulcer [simply a break in the skin of the leg; if there is an underlying problem the skin does not heal and the area of breakdown may even increase in size (chronic leg ulcer)] in their lifetime. Of these, 50% are caused by chronic venous insufficiency, half of which are related to previous venous thrombosis.

4. What are the risk factors for DVT?

Immobilization is a general term that includes many conditions, like prolonged air flights [more than 3 hours], long distance driving [more than 4 hours], recovery time with bed rest, sedentary life style, prolonged sitting etc.

All the factors mentioned above increase the risk of DVT, the most important of which being immobility, trauma and surgery, and oral contraceptives [not in percentage, but in number]. However, the individual risk depends on the combination of factors.

5. How can DVT be prevented?

The object of all thrombosis prevention is to prevent clot formation in the deep veins of the legs.

Mechanical appliances aim at preventing venous stasis. Elasticated compression stockings reduce the volume of the venous bed and thus significantly increase the rate of venous flow. Intermittent compression cuffs act in a similar way. Active [voluntary] movements of the leg alone achieve the same result by increasing the amount of arterial inflow and speeding up venous return. Leg elevation accelerates venous return as well.

These measures are enough for the minimal risk group. For the major risk group, apart from these measures, some form of anticoagulation is needed.

Heparin [a drug that makes blood thinner] is used in cases with minimal to moderate risk and before any type of major surgery. Is given subcutaneously once or twice a day. For people with major risk, it may be given every 8 or 12 hours. For people with extremely high risk or when there is a confirmed hypercoagulable state, warfarin may be used in the long-term to prevent thrombosis.

6. What about superficial venous thrombosis [SVT]?

Superficial thrombosis is the formation of thrombus in a superficial vein of the limb; it may occur in varicose veins [more common] or in a normal vein. It is entirely different condition from DVT, as the risk of pulmonary embolism is minimal and the risk of chronic venous insufficiency is nil. However, it is always accompanied by peri-venous inflammation causing pain and redness of the skin. It causes a lot of discomfort that may last for months, but the risk for the patient’s health is minimal. Only in cases that the thrombosis spreads to the root of the limb pulmonary embolism is a danger and immediate surgery to disconnect the superficial from the deep veins is indicated.

Treatment consists in anti-inflammatory ointments or hyaluroinoids, localized pressure and compression bandage with full mobilisation.

7. What can someone do to prevent thrombosis in specific conditions [in cases with minimal or no risk]?

The mechanical measures suffice in most cases.

• Leg elevation when possible
• Active movements of the legs
• Walking at frequent intervals, even for small distances [i.e. during flights]
• Drinking plenty of fluids
• Below the knee Class II [18-24mmHg pressure] stockings
• Subcutaneous fractionated heparin may be used in high risk conditions, like when someone had a previous DVT and is due to have a more than 8 hours flight]

8. What about after surgery?

The risk is reduced with early and adequate mobilization. Before, during the procedure and during your hospital stay, your surgeon will take all the prevention measures. For most day case procedures the risk is minimal, therefore walking and below knee stockings for a week or till the patient is back to normal suffices. Occasionally, fractionated heparin may be prescribed, especially when recovery is estimated to be longer and the patient’s mobility affected.

For people operated for varicose veins, the risk following surgery is minimal [less than 1%] and is more likely to happen the first week following surgery, till complete mobility is achieved. Traveling [including air-travel] following surgery can be undertaken when the patient feels well, usually a week to ten days after an up to major procedure, with no increased risk. However, in these cases, the risk is the same as for the rest of the population, therefore the conservative measures described above are essential.