DVT flying advice reassessed

“Sitting in a window seat during a long flight can increase the risk of deep vein thrombosis,” according to The Daily Telegraph. It has long been known that flying is associated with an increased risk of deep vein thrombosis (DVT), a type of serious blood clot in a major vein, but new US guidance has looked at a range of factors that could potentially raise the risk.

Those of you thinking of booking your summer holiday might be interested to know that flying in cramped budget seats, while often annoying, presented no greater risk than flying in business class. And while pricey booze available during a flight can prove wallet-damaging, the guidelines say there was no firm evidence that drinking it could bring on DVT. However, sitting by a window during a long-haul flight was associated with a greater risk because of the limited opportunities for walking around. People’s age, previous DVT and recent operations were among the other factors found to raise DVT risk.

The evidence-based guidelines were produced by the American College of Chest Physicians to address the risk of both DVT after long-haul flights and the potentially fatal lung clots (pulmonary embolisms) that can follow. The guidelines also include recommendations about the best ways for travellers to reduce their risk of DVT.

The guidelines seem to debunk the long-held assumption that a lack of legroom causes DVT. This much-debated phenomenon is often referred to as “economy-class syndrome”.

It is long established that inactivity is associated with DVT, and so some people believe that the lack of legroom when flying in economy class can increase the risk of developing a blood clot. This has led to the theoretical phenomenon being dubbed “economy-class syndrome”.

Some have also suggested that dehydration is more common during economy travel and may increase the risk of DVT. However, the existence of this so-called “economy-class syndrome” is controversial and has never been proven.

Deep vein thrombosis or DVT is when blood clots form in a deep vein. A clot that develops in a vein is also known as ‘venous thrombosis’. DVT most commonly affects the leg veins or deep veins in the pelvis. It can cause pain and swelling in the leg but in some cases there may be no symptoms.

DVT can lead to the potentially life-threatening condition known as a pulmonary embolism. This occurs when a clot breaks off into the bloodstream and travels to the chest, where it blocks one of the blood vessels in the lungs.

Experiencing DVT and pulmonary embolism together is known as venous thromboembolism (VTE), which is a condition that can be life-threatening. Each year more than 25,000 people in England die from VTE contracted in hospital. This is approximately 25 times the number of people who die from MRSA. VTE occurs in hospitals as a result of patients lying sedentary in bed for extended periods following an operation. In recent years the NHS and Department of Health have run a major programme of measures to help reduce the rates of VTE developed in hospitals. For example, many patients are now given a VTE risk assessment when being booked into hospital.

In the UK each year about one person in every 1,000 is affected by DVT. Anyone can develop it but there are certain known risk factors that include:

The advice comes from new evidence-based guidelines produced by the American College of Chest Physicians (ACCP). The findings were published in the February issue of the medical journal CHEST.

The guidelines are extensive, running over hundreds of pages. They detail both the risk factors for DVT and measures to diagnose and prevent DVT.

The evidence review that informed the guidelines looked at a range of risk factors for the development of DVT in long-distance travellers. These included the use of oral contraceptives, sitting in a window seat, advanced age, dehydration, alcohol intake, pregnancy and sitting in an economy seat compared to business class.

The reviewers conclude that developing DVT or pulmonary embolism from a long-distance flight is generally unlikely, but that the following factors increased people’s risk:

The finding relating to window seats was discussed further. The study authors suggest that long-distance travellers sitting in a window seat tend to have limited mobility, which is responsible for their increased risk of DVT.

However, the review did not find any definitive evidence to support the theory that dehydration, alcohol intake or sitting in an economy seat (compared with sitting in business class) increases the risk of DVT or pulmonary embolism during a long-distance flight. On this basis, they conclude that travelling in economy class does not increase the risk of developing a blood clot, even during long-distance travel. However, they believe that remaining immobile for long periods of time does.

Overall, the study authors say that “symptomatic DVT/PE [pulmonary embolism] is rare in passengers who have returned from long flights”, but that the association between air travel and DVT/PE is strongest for flights longer than 8-10 hours. Furthermore, most of the passengers who do end up developing a DVT/PE after long-distance travel have one or more risk factors.

For travellers on flights longer than six hours who have an increased risk of DVT the new guidelines recommend:

The guidelines do not recommend compression stockings for long-distance travellers who are not at increased risk of DVT.

The guidelines advise against using blood-thinning aspirin or anticoagulant therapy to prevent DVT or pulmonary embolism for most people. They suggest that anti-clotting medications should be considered on an individual basis only for those at particularly high risk of DVT, as in some cases the risks may outweigh the benefits.