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Orthotic Consultation for treatment or prevention of DVT, including measurement/fitting, can be arranged by our qualified clinical team –  Contact us for more information on what is available or book an appointment.

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Causes of DVT

Blood clots are formed when blood stops moving and coagulates. This natural mechanism ensures blood flow will stop following minor accidents and cuts.

If a clot (known as a thrombus) forms in the leg's deep veins, DVT occurs.

If the clot is dislodged and begins to circulate in the body, it can cause a significant obstruction in the narrower vessels of the heart or lungs – known as venous thromboembolism (VTE). It is the dislodged clot that presents the danger.

Inactivity as the Culprit

It is essential to realise that it is not just long-distance air travel that puts people at risk. Sitting in one position for too long is a significant factor. The famous label “economy class syndrome” can also arise in business class or during long car, bus or train journeys – inactivity is the real culprit.


Why is flying a risk?

The risk for DVT while flying is increased because of the reduced cabin pressure at high altitudes, which causes fluid to pass from the blood vessels into the surrounding tissue, causing thickening of the blood. Normal movement of the calf muscle when walking helps pump blood from the legs to the heart, but with the loss of fluid while sitting for long periods, the blood can thicken, solidify and form a clot in the deep veins of the leg.

In most cases, the clots do not dislodge from the leg and merely cause pain, and they may also be symptomless.

Other collected data suggest the lower oxygen level experienced during flight can lead to an increased tendency for blood coagulation.

How common is DVT?

One recent UK study concluded that, “symptomless DVT might occur in up to 10% of long haul airline travellers”, but Dr Jack Hirsch, a clot expert at McMaster University in Hamilton, Ontario, suggested in the Lancet that this might be overstating the risk and that the study methods had their shortcomings.

Over one billion people travel by air each year. Professor Caprini estimates that the death rate during flight is one in 3.25 million passengers, with VTE of the lung accounting for 18% of deaths. “Based on reported cases, it may be concluded that VTE is very rare. However, it may develop during or immediately after a flight or even days later. Increased air travel has made the problem more important.”

What are the risk factors for DVT?

Risk factors for developing DVT, and VTE, include:

  • blood clotting disorders
  • varicose veins
  • cancer
  • heart failure
  • pregnancy
  • using oestrogen-containing medications
  • recent surgery or trauma
  • smoking
  • being overweight (body mass index > 27)
  • age over 40 years

Aircraft cabin-related risk factors can further increase travellers’ risk:

  • dehydration
  • immobility

How do I avoid DVT?

If you are planning a long trip you could mention this to your doctor at your next visit. Your doctor can then assess any risk factors you may have.

Even though the link between clots and long trips is still being investigated, there are many things long distance travellers can do to minimise any potential risk.


What are some prevention tips against DVT?

Steps to help prevent DVT on long-haul airline flights and during long car, train or bus journeys include:

  • do ankle and knee exercises every half hour while seated
  • walk down the aisles regularly, or if travelling by car, frequently stop, get out and take a walk
  • wriggle toes frequently
  • drink plenty of water (one litre every five hours)
  • go easy on alcohol and caffeine
  • take aspirin (if advised by your doctor)
  • wear knee-high compression stockings (if advised by your doctor).

Many long-distance travellers favour compression stockings to reduce the risk of blood clots. Wearing a compression stocking counteracts the loss of fluid into the tissue of the leg and so reduces the risk of clotting. Some doctors are now routinely recommending these stockings to people over the age of 35 who will be travelling for more than four hours.

Compression stockings are not all the same – there are different compression levels. For most travellers, Class 1 hosiery is needed to prevent swelling of the legs. This compression stocking class is also suitable for mild varicose veins and those with tired, aching legs during pregnancy.

Travellers with existing health problems such as heart problems, mild to severe varicose veins, or those who have recently undergone surgery, should see their doctor first to ensure they get a suitable compression class. Class 2 and Class 3 compression stockings should only be used if a doctor recommends it.



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