“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 overpriced 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”.

 

What is “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 your 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.

 

What is DVT?

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.

 

Who is at risk of DVT?

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:

• increasing age
• pregnancy
• previous venous thromboembolism
• family history of thrombosis
• medical conditions such as cancer and heart failure
• inactivity (for example after an operation or on a long-haul flight)
• being overweight or obese

 

Where has the advice come from?

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.

 

What do these guidelines tell us?

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:

• previous DVT or pulmonary embolism or known ‘thrombophilic disorder’
• cancer
• recent surgery or trauma
• immobility
• advanced age
• oestrogen use, including oral contraceptives
• pregnancy
• sitting in a window seat
• obesity

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.

 

What can be done to prevent DVT?

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

• Frequent walking about during the flight.
• Calf muscle stretching.
• Sitting in an aisle seat if possible (as you are more likely to get up and move around in flight).
• Wearing below-the-knee compression stockings that are ‘graduated’, meaning they apply greater pressure lower down the leg. They are designed to put pressure on the lower legs, feet and ankles to increase bloodflow, thereby making it harder for a clot to form.

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.

Links To The Headlines

DVT risk raised by sitting in the window seat. The Daily Telegraph, February 7 2012

Dangers of DVT: Why you should avoid the window seat on the plane (even in First Class). Daily Mail, February 7 2012

Links To Science

Bates SM, Jaeschke R, Stevens SM, et al. Diagnosis of DVT : Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest 2012;141;e351S-e418S. Published online February 7 2012

Press release

American College of Chest Physicians: New DVT Guidelines: No Evidence to Support "Economy Class Syndrome": Oral Contraceptives, Sitting in a Window Seat, Advanced Age, and Pregnancy Increase DVT Risk in Long-distance Travelers. February 7 2012

An 83-year-old woman has been implanted with the world’s first “3D printer-created jaw”. Using cutting-edge laser manufacturing techniques, doctors and metal experts were able to build up layers of titanium to form a custom metal jawbone to exactly fit her face. The metal jawbone was then inserted into her lower jaw, replacing a large section of bone that was destroyed by a chronic infection.

The technique of 3D printing has been used to build prototype products for some time, but in recent years scientists have begun experimenting with the medical possibilities offered by the process. In this case, a specialist metalwork company called Layerwise was able to translate 3D bone scans into a custom jaw. The company had previously used the process to make bone-shaped prostheses and dental implants. To make a full jawbone, the implant team had to overcome a number of challenges, such as how to encourage muscles to attach to the implant and how to incorporate the nerves necessary for normal movement of the jaw.

While 3D printing is still very much an experimental medical technique, scientists are even currently devising ways in which they might use it to produce whole organs, which are either “printed” by sandwiching layer after layer of living cells on top of each other or created by building scaffolds for cells to grow on.

 

Why did the woman need a new jaw?

The woman had a condition called osteomyelitis, a type of damaging bone infection usually caused by bacteria or, less often, by a fungal infection. It can occur when infections in nearby skin, muscle or tendons spread to a bone, or when an infection spreads from another part of the body through the blood stream. Depending on the nature of the infection and the health of the patient, osteomyelitis  can cause permanent damage to bones. The condition can be treated with antibiotics to get rid of the infection and prevent further damage, but sometimes surgery will be needed to remove dead bone tissue from around the site of the infection.

If a section of bone tissue is removed, surgeons can close the space by grafting in bone taken from elsewhere in the body or by inserting specialised filler materials that promote regrowth of the surrounding bone.

In this case, the patient had a progressive, chronic form of osteomyelitis which affected nearly her whole jawbone. This meant that she experienced permanent destructive changes which could not be treated by antibiotics alone. Because of the patient’s age, reconstructive surgery using conventional methods would have been risky. Therefore, her medical team decided to attempt to use a bespoke titanium-based implant to replace nearly her entire lower jaw.

 

What is 3D printing?

3D printing broadly encompasses a variety of different techniques. All the techniques involve using computers to knit together layers or particles of materials to form a new 3D structure. At present, doctors, scientist and technicians use 3D print technology to build implants out of metals, plastics and ceramics and are experimenting with making 3D structures using synthetic bone materials  and even living cells.

It can have several advantages over traditional manufacturing techniques, most notably the ability to create highly accurate bespoke structures such as dental implants. In the case of the new jaw implant, the process offers the option to create a structure that can perfectly fit the dimensions and contours of the patient’s face. Given the complexity involved, using an off-the-shelf implant is not practical.

To create the implant, the manufacturer Layerwise used a type of 3D printing called “selective laser melting”. During the process, heat-producing lasers are focussed on a bed of metal powder so that particles are precision-fused to form a 3D structure. This process is different to traditional metalwork, in which a shape is created by starting with a solid block and removing metal, similar to sculpting. Instead, the 3D printing process allows a shape to be built by adding tiny, intricate layers of particles, much like building a structure layer-by-layer from microscopic building blocks.

 

Has it been used medically before?

Doctors have previously used 3D-printed metal implants for dentistry and small bone prostheses, but this was the first time it was used to make a full jawbone. The benefit is that these custom-made prostheses can be modelled and shaped to fit the unique structure of someone’s surrounding bones. The surgeons revealed that surgery to implant the jaw took less than four hours and that the patient could speak and swallow again the day after surgery. This rapid recovery of function is encouraging.

It is likely that this technique will be investigated by other surgical groups, but the current reports relate only to the treatment of a single patient with chronic bone infection. It is not yet known whether it could be successful in wider facial reconstructive surgery, for example following trauma.

 

What might it be used for in the future?

While there are no guarantees that experimental lab techniques can be turned into usable treatments, medical 3D printing has been a hot topic in the news in recent years.

For example, in November 2011, BBC News reported that a team of scientists from Washington State University had used “a bone-like ceramic powder” to make a bone-like material that acts as a scaffold for new cells to grow. However, his experimental technique had not been used in people at the time of reporting.

Scientists are also looking at whether it is possible to use 3D printing to create important structures such as heart valves and even whole organs. A variety of systems is being tested in the lab, from creating 3D scaffolds for cells to populate to layering cells themselves.

Much of this cutting-edge technology is years away at the very least, but the possibilities are great and very exciting, as highlighted during a talk by Dr Anthony Atala at last March’s TED conference.

Links To The Headlines

World's first 3D printer-created jaw fitted to 83-year-old. Daily Mail, February 7 2012

Transplant jaw made by 3D printer. BBC News, February 7 2012

3D printer builds new jaw bone for transplant. The Daily Telegraph, February 7 2012