DVT, or deep-vein thrombosis, is a condition which occurs when a blood clot forms in a deep leg vein (typically the calf or thigh). If the clot stays put, stuck to the wall of the vein, it causes redness and swelling to the area. But if part of it breaks off it can travel to the lungs (pulmonary embolus) and cause serious illness or even death. It can also be a contributory cause of a stroke or heart attack. Unfortunately some DVTs cause no symptoms, for instance in the pelvis, and the first that is known of the condition can be a pulmonary embolism.
Why does it happen when flying?
Travel-related DVT is caused by sitting still for long periods of time in cramped conditions. The blood flow slows down and the blood collects in the legs when in a sitting position. Slow blood flow is more likely to cause a clot to form. A “long period of time” is considered to be four hours or more, and DVTs can be caused not only by flying but also travelling by car, coach or train.
How likely am I to get a DVT?
Not all travellers have the same risk of developing a DVT. The following factors raise your risk:
- Being a woman
- Being over 40
- Pregnancy or having given birth recently
- Previous DVT or pulmonary embolism unless you are taking anti-coagulant medication
- Operation in the two months prior to travel (especially surgery to legs or abdomen)
- Close relation who has had a DVT or pulmonary embolism, particularly if they were under 35 at the time
- Taking the contraceptive pill
- Taking HRT
- Being very short, very tall or obese
- Having your leg in plaster
- Suffering from blood-clotting disorders
- Cancer (past or present)
- Suffering from IBS
- Having had a recent bout of pneumonia
- Heart problems such as recent heart attack or heart failure
Even if you have one of the risk factors above, the chance of suffering a DVT is still very small. If you have two of the risk factors, then the chances of having a DVT doubles, but this is still a small risk.
As some DVTs are symptom-free and some do not present themselves until a while after the flight it is difficult to obtain accurate figures. However, it is thought that one DVT occurs for every 4,656 flights of more than four hours. Notwithstanding the small risk, trying to reduce excess weight and giving up smoking makes sense.
What else can I do to prevent a DVT?
Prevention of DVTs is vital since if one occurs on a long-haul flight, it may not be possible to get help quickly.
Make sure you move around the cabin every hour or so when possible and also stand on tiptoes to exercise the calf muscles. Avoid crossing your legs as this reduces blood flow. If you are travelling in First or Business Class, elevate your legs. If you have a break in your flight, make sure you take the opportunity to walk rather than sitting in the terminal waiting for the next leg of your journey.
There are also exercises which you can do in your seat to reduce the risk of DVTs. Click here for a sequence of six exercises which should be repeated half-hourly.
Avoid alcohol which causes dehydration (and makes your blood more “sticky”) and sleeping pills on night flights as they cause immobility. Drink plenty of water to stay hydrated (at least a litre per five hours in the air).
Elastic compression stockings or “flight socks” help to stop the blood pooling in your lower legs and can be bought online, at many local chemists or at the airport. Badly fitting compression stockings can raise the risk so take advice if necessary to make sure you get a good fit. If you have a plaster cast on your leg it will normally need to be split for the flight so seek guidance from your doctor or fracture clinic.
Although low dose aspirin is often taken to prevent clots in arteries, thereby reducing the likelihood of heart attack or strokes in those at risk, there is no evidence to show that aspirin is effective in clot prevention in veins. If you are at high risk of a DVT, then an anti-coagulant such as an injection of heparin may be prescribed by your doctor. This would normally apply only to cancer patients, those with thrombophilia (a condition where your blood has a tendency to clot) and those who have had major surgery in the last month.
Any more advice?
If you develop pain in your chest, difficulty breathing or pain, swelling or redness in your calf or thigh after a flight, seek urgent medical help.
Swelling in the ankles during flights is relatively common and not a sign of DVT.