Deep vein thrombosis (DVT) leading to pulmonary embolism (PE) continues to be a relatively common cause of death in healthy young women. Although the risk of DVT / PE is well known to increase with the use of the combined contraceptive pill, there is less awareness that air travel, and to a lesser extent car or coach travel, are more frequent causes of DVT and PE. The consequences of developing a DVT or PE are also underappreciated. In the short term, patients will almost inevitably take time off work as they manage the symptoms and undergo treatment, and significant health problems can develop in the long term. Most significantly, one third of PEs are fatal, often depriving the family of its principal breadwinner and causing psychological distress to their family.
The Warsaw Convention (1929) was the first international legislation designed to regulate liability for the transport of goods and individuals by air. The primary aim of the Convention was to protect a young aviation industry from the financial consequences of virtually inevitable tragedies. However, the Convention also sought to balance the rights of the passenger by safeguarding them against injury and death where the airliner had not taken all measures available to them. In 2005, the Warsaw Convention was at the centre of a group litigation in which the House of Lords was asked to consider whether flight-induced DVT could amount to an ‘accident’. Rejecting the appeal, the House of Lords held that an accident constituted “…an unexpected or unusual event or happening that is external to the passenger” and that DVT during air travel did not amount to an accident as the causation of the DVT was an internal reaction of the passenger.
However, if the Claimants to this group litigation could have proven that flight-induced DVT was reasonably foreseeable, that the risk of DVT could have been reduced by the airliner and that the airliner failed in their duty to reduce this risk, then, on the balance of probabilities, the 2005 judgement would have been different6. As DVT can lead to PE and as most DVTs are preventable, an increasing number of claims brought by employees, who have suffered a DVT during frequent or long-haul air travel have been submitted against their employers. This article seeks to explain DVT and its association with flying, and intends to start a debate on whether employers have a duty of care to their employees travelling for and on behalf of a company.
What is DVT?
DVT is the development of a blood clot in one of the deep veins. Usually, this is in the leg or pelvis, but it can occur in any deep vein. Obstruction of the vein leads to higher vein pressures and swelling of the limb below the obstruction. The resultant inflammation causes pain, tenderness, leakage of fluid into the tissues (oedema) and redness of the overlying skin. Part of this clot can
easily detach and flow with the blood stream up the inferior vena cava, through the right side of the heart and into the pulmonary artery causing a PE which, if large enough, may obstruct the circulation to the lung and strain the heart, causing almost instant death.
How common is DVT?
Every year 100 in every 100,000 people develop DVT, with 40/100,000 developing pulmonary embolism. PE is thought to be responsible for 60,000 deaths per year in the United Kingdom.
What are the consequences of DVT?
There are significant short and long term effectsfor anyone suffering DVT. Aside from the symptoms described above, anticoagulation routinely prescribed for 3-6 months to reduce the risk of further thrombosis is effective, but also increases the risk of haemorrhage that can frequently require hospital admission. In addition, there is an increased risk of more serious bleeding in the
event of an injury. Following the initial symptoms, 40-60% of patients with DVT will develop long-term complications due to chronic venous insufficiency or ‘post-thrombotic syndrome’.
The typical symptoms include aching, swelling, heaviness of the leg and skin damage with brown discolouration. The inflammation associated with DVT causes scarring of the venous valves making them incompetent and allowing blood to reflux down the leg. The result is chronic high blood pressure in the veins causing inflammation of the tissues that may lead to ulceration of the skin, which is severely debilitating, painful, unpleasant, often malodorous and always difficult to heal. In addition, DVT confers a significant economic burden. This is not just confined to the cost of treatment: employers in the US lose $50-60,000 in productivity-related activity foreach DVT. The total cost of DVT/PE exceeds £640 million per year in the United Kingdom.
Travel and the risk of DVT
The contraction of the calf muscle during walking pumps blood up the leg veins towards the heart. This calf muscle pump is inactive when sitting or standing, which allows stagnation of venous blood flow known as ‘venous stasis’. This stagnation allows the venous blood to clot within the vein, with that clot or thrombus rapidly growing up the vein until blood flow is adequate to prevent its further extension. Travel by coach or aeroplane involves prolonged periods of immobility as the passenger sits in the same seat for hours, resulting in prolonged venous stasis, which increases
the risk of DVT. Asymptomatic calf vein DVT (diagnosed by ultrasound, but not large enough to cause symptoms) was detected in 10% of people completing two eight hour flights within the same month. Larger studies have confirmed that 1% of people flying for over four hours develop asymptomatic and potentially damaging DVT.
It is likely that falling asleep on an aeroplane or coach reduces mobility further, and is probably an important cause of DVT during travel. The Lancet paper also reports that elastic stockings are highly effective at preventing DVT, and that as such, this is a preventable condition. Frequent flying increases the risk of symptomatic DVT. Taking a second flight within a few weeks allows a
small asymptomatic DVT to start propagating into a more extensive, damaging and symptomatic DVT, and increasing the risk of PE. Two four hour flights in eight weeks more than doubles the risk of a single flight. The risk increases fourfold if three or four flights are taken within eight weeks, and sevenfold for five flights.
What can be done to reduce the risk of DVT?
The risk of DVT in hospital patients is even higher, and not only because the illness or treatment has reduced their mobility and increased venous stasis. Patients often have coexisting inflammation (either as a normal response to surgery or as a direct result of their illness) that increases the coagulability of blood. Doctors have developed strategies to minimise the risk of DVT and PE in their patients. Compression hosiery is almost universally prescribed as it is inexpensive, safe and easy to use. The stockings exert pressure on the leg, compress the veins, reduce the volume of static blood within the leg veins and encouraging more rapid blood flow. Despite the accepted importance of compression stockings in preventing DVT there is evidence that many are ill-fitting, which can compromise their effectiveness in reducing the risk of DVT. As such, the need for a precise fit in order to deliver an accurate pressure profile is essential. IsobarTM stockings are knitted to fit the precise 3D profile of each individual leg. Stockings of this quality delivering 20mmHg compression at the ankle reduce venous transit times by 38%, with 25mmHg compression halving transit times and further reducing the risk of DVT for individuals at high risk. The NHS recommends that all passengers flying for more than four hours should wear compression stockings.
An employer’s responsibility
It is trite that where there is a legal relationship, so too exists a duty of care. Employers are obliged to ensure that they take all reasonable measures to adequately protect their employees against any risks of foreseeable harm. Where an employer fails in their duty to do so, this may result in litigation.
Most employers now have extensive health and safety apparatus that seeks to protect their employees from injury, yet the potential consequences of travel induced DVT / PE do not seem to be appreciated. What, if anything, are companies doing to protect their employees who travel for and on behalf of a company? As businesses globalize, air travel is increasingly common, and so too is the risk of DVT and PE to the employee