What is deep vein thrombosis?

Deep vein thrombosis (DVT) is the formation of blood clots in major veins. The condition is somewhat misleadingly known as “economy class syndrome” due to its link to long distance travel, which has had wide media coverage in recent times. There have been a number of deaths that have received media attention and several studies are now being conducted to establish how strong the link is between the two. So far, researchers have been unable to agree on a conclusion.

It is important 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 major factor, which means the popular label “economy class syndrome” can also arise in business class, or during long car, bus or train journeys – inactivity is the real culprit.
Most airlines now print warnings on tickets and booking schedules, and the topic is covered on in-flight safety videos. Airlines have learnt that it takes time, energy and effort (and millions of dollars) to save a few lives.

According to Professor Joseph Caprini of the University of Chicago, a world authority on travellers’ clots, family doctors, not the airlines, should be taking the flak for these few incidents. At a meeting with New Zealand GPs, he said he would like to see doctors assess all patients for DVT risk factors, particularly as 95% of those at risk show no symptoms.

What causes 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 deep veins of the leg, DVT occurs.
If the clot is dislodged and begins to circulate around the body, it can cause a major obstruction in the narrower vessels of the heart or lungs – known as venous thromboembolism (VTE). It is the dislodged clot that presents the danger.

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 to pump blood from the legs to the heart, but with the loss of fluid while sitting for long periods, the blood can thicken, coagulate and form a clot in the deep veins of the leg.

In most cases the clots do not dislodge from the leg and they merely cause pain. 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.

Prevention tips

Steps to help prevent DVT on long haul airline fights 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, stop frequently, 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).

Compression stockings are favoured by many long distance travellers 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 levels of compression. For most travellers, Class 1 hosiery is all that’s needed to prevent swelling of the legs. This class of compression stocking is also suitable for mild varicose veins, during pregnancy and for anyone with tired, aching legs.

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

How can OLAB  help?

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.