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Travel-related deep vein thrombosis: latest guidelines

John H Scurr
BSc MB BS FRCS
Consultant Surgeon
The Lister Hospital
London
T:020 7259 9216
F:020 7259 9221
E:medleg@mailbox.co.uk
W:www.jscurr.com

Deep vein thrombosis (DVT) has usually been associated with hospitalisation, but more recently great interest surrounds thromboses occurring following air travel. Immobility, damage to the vein walls and a change in the blood's ability to coagulate are three important factors leading to the development of a DVT. Some people are at greater risk of developing a DVT, and these include older people, people with a previous history of DVT and those with concurrent illnesses. DVT occurs most commonly in the legs. Such thromboses are often asymptomatic, becoming symptomatic only when the clot extends up into the main, femoral or pelvic veins. At this point there is a risk that fragments can break off, travelling to the lungs to give rise to pulmonary embolism.

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Increased awareness
DVT in relation to travel and in particular air travel, has received considerable publicity. Why are we now seeing this problem? Why has it caused so much concern? First, for the majority of people travelling by whatever means, there is no serious risk of either developing a symptomatic blood clot or a pulmonary embolism. The majority of people who develop blood clots have additional risk factors and could probably be identified before travel. One of the reasons why we are seeing more people now presenting with blood clots is that people travel more frequently and they travel for greater distances. An increased awareness of the problem has also led to more frequent diagnosis. With an increased awareness of this particular problem, prevention and treatment become important.
A young fit person travelling by whatever means is unlikely to have any serious problems. Some people, however, do have increased risks, and these risk factors can usually be identified (see Table 1). A past history of venous thromboembolism, increasing age, recent surgery and a serious concurrent illness all predispose to the development of DVT.

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There is no evidence that women in the early stages of pregnancy have an increased risk of thrombosis.
Most of the risk factors can be identified by taking a simple pretravel history. Occasionally, we see young people with no apparent risk factors developing a spontaneous DVT. In many instances they have an underlying thrombophilia, and this in itself produces an additional risk.

Assessing patients
As a nurse practitioner, you are likely to be involved in assessing the risk of travel and providing appropriate advice. It is very important to reassure the majority of travellers that there are no serious risks and that travel can be completed safely. There are greater risks associated with travelling than flying itself, including travel to areas where malaria and HIV are endemic.
Once it has been established that there are no significant risk factors, patients should be advised accordingly (see Table 2). First, they should purchase a pair of graduated compression stockings and wear them for the duration of the flight. They should also be encouraged to take exercise before boarding the aircraft, on the plane and after disembarkation. It is important to drink plenty of water and avoid drinking too much alcohol.

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If symptoms do develop subsequent to the flight, they should be reported to a doctor.

Prevention and treatment
Graduated compression stockings have been shown to be effective in reducing the risk of deep vein thrombosis in hospitalised patients and, in small pilot studies, in travellers. One of the benefits of wearing graduated compression stockings is that they reduce the swelling often associated with prolonged immobility.
What should one do for patients who have additional risk factors? Those passengers with a past history of DVT and elderly passengers with concurrent illnesses are probably at increased risk. Even in this group of passengers the risk is relatively small. They too can be offered the same advice as the previous group. Additional prophylaxis can be given using low-molecular-weight heparin (LMWH). Clearly, a clinical decision as to the advisability of giving LMWH needs to be made before giving it. While LMWH has been shown to be safe, effective and of proven benefit in hospitalised patients, clinical studies assessing it use in travellers are yet to be completed. However, many general practitioners and other physicians are prescribing LMWH for their passengers who they consider to have additional risk factors.
A passenger travelling long haul may expect to receive 20mg of enoxaparin sodium (Clexane; Rhone-Poulenc Rorer) the day before travel and on the morning of travel. The same procedure can be repeated for the return flight.
One must remember that clinical studies to evaluate the effect of prophylaxis during long-haul travel are still being carried out. No method of prophylaxis is ever completely effective.
All passengers should be advised that, if they develop any symptoms of swelling or chest symptoms, they should report these to a doctor and make sure the doctor knows they have had a period of recent travel.
A DVT is a treatable condition, and this may prevent the passenger going on to develop a pulmonary embolism (see Table 3). Even pulmonary emboli are treatable - often presenting as chest symptoms and misdiagnosed as a chest infection. Antibiotics are effective in treating a chest infection, but they may be of little value when the underlying cause is a pulmonary embolus.

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A high index of suspicion is required in anybody who gives a recent history of travel. The diagnosis of DVT can be made noninvasively using duplex ultrasound imaging. The diagnosis of pulmonary embolism is more difficult. Indirect evidence can be obtained by using a duplex ultrasound scan of the leg and making a diagnosis of a DVT. An ECG may show typical abnormalities, and, finally, a spiral CT will show evidence of pulmonary embolism.
Any patient with a substantial DVT in the deep veins extending above the knee and any patient with a pulmonary embolism should receive full intravenous heparinisation followed by a period of warfarinisation. 
There are a number of new protocols for the treatment of DVT beginning to emerge using LMWH. My own personal preference is to admit anybody with an established DVT or a pulmonary embolism for hospital treatment.

Conclusion
Travel thrombosis is a well-recognised medical condition. Some travellers are at increased risk, and the additional risk factors can be identified. For the majority of passengers, though, travel remains very safe, and small asymptomatic DVTs are of no consequence. However, all travellers should be aware of the condition and take appropriate precautions, and nurses should obtain a history of travel from anybody presenting with leg or chest symptoms. Early diagnosis and appropriate treatment can help avoid the more serious consequences.

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