It occurs when restricted blood flow leads to the formation of a blood clot in a deep vein of the leg. Symptoms include a swollen or painful calf or thigh; in rare cases, part of the clot moves to the lungs, possibly causing a pulmonary embolism (blocked blood vessel) that, if severe, may cause the lungs to collapse.
Flying and DVT
Of course, DVT/PE events (also called venous thromboembolism) aren’t caused only by traveling. Each year it occurs in as many as 900,000 people in the US, according to the CDC, and can be fatal in up to 10 percent of the cases.
Still, Professor Mark Whiteley, a consultant venous surgeon and phlebologist, a “The things that cause clots are the Virchow’s Triad [named after German physician Rudolf Virchow]. These are changes in the blood, changes in the blood flow and changes in the vessel wall. Any one of those can cause a clot.”
According to Whiteley, “When you fly, you have a change in the flow, since you’re just sitting there, so the blood isn’t flowing as it should, and you’re up in the air, so you have decreased oxygen and have changed the blood, and then, finally, if you have varicose veins, then you’ve changed the wall of the vein as well. So when you fly, you’ve got the perfect storm for DVT.”
Who Gets It?
Anyone can develop DVT, but it becomes more common over the age of 40. As well as age, there are a number of other risk factors, including:
•Having a history of DVT, pulmonary embolism, or a family history of blood clots
•Being inactive for long periods of time
•Having blood vessel damage – a damaged blood vessel wall can result in the formation of a blood clot
•Having certain conditions or treatments that cause your blood to clot more easily than normal – such as cancer (including chemotherapy and radiotherapy treatment), heart and lung disease, thrombophilia, and antiphospholipid syndrome, sometimes known as Hughes syndrome
•Being pregnant, as your blood clots more easily
•Being overweight or obese.
How to Avoid It
When flying, make sure you:
•Stay hydrated – drink plenty of water and avoid drinking excessive amounts of alcohol
•Do calf exercises at least every half-hour – raise your heels, keeping your toes on the floor, then bring them down ten times. Then raise and lower your toes ten times
•Avoid taking sleeping pills because they can cause immobility
•Take occasional short walks when possible
•Wear loose, comfortable clothes and elastic compression stockings. These are usually knee-length but can also be thigh-high. They work by putting gentle pressure on your leg and ankle to help blood flow. They come in various sizes with different levels of compression. Class 1 stockings have the lowest compression (with a pressure of 14-17 mmHg at the ankle) and are generally sufficient to prevent DVT. To state the obvious, it’s important that compression stockings are worn correctly. Ill-fitting ones could further increase the risk of DVT.
Superficial Vein Thrombosis
SVT – superficial (or shallow) vein thrombosis – is an inflammatory condition of the veins caused by a blood clot just below the surface of the skin. Symptoms include painful, hard lumps underneath the skin and redness of the skin. “If you have SVT, you should have a scan,” Whiteley advises. “If that clot is within 5cm (0.4 inch) of a junction to the deep vein, it can turn into a DVT. If it is close to a deep vein then an anticoagulant [blood-thinning medicine] should be offered. Unfortunately, in many cases patients are given antibiotics, which are useless for this, and advice about flight socks.”
On a wider point (and something for a future article), Whiteley points out that while it is known that people with varicose veins are at risk of both SVT and DVT, a significant proportion of the population are unaware of whether they have varicose veins or not, because most instances are not on the surface and so don’t show. For those people with varicose veins, leg ulcers or a family history that might indicate problems are likely, he recommends having a peremptory scan.