Deep vein thrombosis (blood clots)
Deep vein thrombosis (DVT) is a term used to describe the formation of a clot, or thrombus, in one of the deep veins, usually in the lower leg. DVT can occur as a result of periods of immobility, for example following surgery, but can occur spontaneously in otherwise healthy persons.
DVT has been known to occur following long haul air travel and was dubbed 'economy class syndrome'; however this term is misleading as DVT has also been reported following car and train journeys. The preferred term is now travel related DVT or travellers' thrombosis. However, the evidence for an association between long haul travel and DVT remains under study.
Risk for travellers
A recent history of travel was found in 24 per cent (39/160) of patients who presented with venous thrombosis. A further study concluded that the risk of DVT was increased during the two weeks following a long haul flight. Long-haul flights that typically last for at least eight to 10 hours are considered highest risk.
Several other factors have been identified from studies of surgical patients as increasing the risk of DVT. These include:
- Those over 40 years of age
- Previous history of DVT or pulmonary embolism
- Haematological (bloo) disorders (e.g. thrombocythemia, antithrombin deficiency)
- Pregnancy and puerperium
- Malignancy (cancer)
- Congestive cardiac failure or recent myocardial infarction
- Recent surgery
- Oestrogen therapy (e.g. oral contraceptive pill)
Signs and symptoms
Many cases of DVT cause no symptoms. However, some persons may develop pain in the calf accompanied by swelling and redness. The affected area is often warmer and there may also be swelling. If the vein is completely occluded there may be cyanotic (blueish) discoloration of the limb and severe oedema.
Pulmonary embolus is a serious complication and can be life threatening; sudden onset of breathlessness is the most common clinical feature, though it can also cause severe chest pains.
The main aim of therapy is to prevent pulmonary embolism, and anticoagulation treatment with heparin and warfarin is usually commenced. Warfarin therapy is usually continued for between 3-6 months, and patients are advised to wear a compression stocking on the affected limb for a period of time.
There are a number of measures that can be taken to reduce the risk of travel related DVT. All travellers intending to travel long haul should be aware of these.
- Avoid dehydration and excessive consumption of alcohol
- Regularly flex and extend the ankles which will encourage blood flow
- Avoid stowing hand luggage under the seat as it restricts movement
- Do not wear constrictive clothing around the waist or lower extremities.
- Compression stockings:
Travellers at an increased risk of DVT are advised to consider the use of compression stockings, which may reduce the risk of DVT and also reduce swelling associated with long haul flights. It is vital that such compression stockings are well fitting and correctly measured as ill fitting stockings could further increase the risk of DVT.
There is good evidence that aspirin is useful in preventing arterial thrombosis, but its role in the prevention of venous thrombosis is less clear. One study found that there was a reduction in the rate of DVT and pulmonary embolus in patients with hip fractures who were given aspirin. However, when this was data was applied to rates of traveller's thrombosis it was found that in order to prevent one case of DVT, 17,000 persons would have to be treated with aspirin. Furthermore a Cochrane review noted that approximately one patient in 40 taking low dose aspirin would develop gastric (stomach) irritation. Due to insufficient evidence supporting the use of aspirin, guidelines from the American College of Chest Physicians recommend against its use for DVT prevention associated with travel. UK guidelines support this view and agree that aspirin should not be used for the prevention of DVT in travellers.
Low molecular weight heparin (LMWH)
The value of LMWH in the prevention of DVT in high risk persons is well established. However, its use in the prevention of travel related DVT is less clear.
Most medical practitioners recommend the use of LMWH for travellers at high risk of developing DVT, for example a history of previous DVT or pulmonary embolus.
A suitable regimen of heparin should be discussed with a haematologist, and the traveller or companion trained in its administration.