Economy
class syndrome does not discriminate – even business class travellers are at
risk. The latest research about travellers’ thrombosis is discussed. By Hazel Cullinane
Travel
health advice for business travellers is provided by many sources including
independent travel clinics, GP practices and occupational health departments.
However, much of this advice has concentrated on travel health risks while
abroad and not on the health risks associated with the journey itself.
The
issue of travellers’ thrombosis or the misleading term "economy class
syndrome" has created much media attention over the last year since the
tragic death of 28-year-old Emma Christofensen of a pulmonary embolism (PE),
following a flight from Australia to London. The issue of aviation health has
also captured the attention of the House of Lords, with the Select Committee on
Science and Technology producing a report on air travel and health, in November
2001. This was following extensive oral and written evidence from various
parties including the airline industry, aircraft manufacturers, passenger
interest groups and medical experts.
While
the media has raised the issue of travellers’ thrombosis it has also raised
public concern regarding the safety of air travel. Air travel is regarded as
one of the safest forms of transport with nearly two billion passengers
travelling globally every year2. With the number of business travellers
doubling over the last 20 years occupational health practitioners are well
placed to provide advice on travel health and related aviation health issues.
This
article aims to provide information and advice for occupational health
practitioners to address the issue of travellers’ thrombosis with their
organisation’s business travellers.
What
is travellers’ thrombosis?
It
has been known for many years that slowing of venous flow or stagnation of
blood can be a risk factor for the development of deep vein thrombosis (DVT)3.
Immobility can slow circulation. This is one of the reasons why health care
professionals encourage patients to mobilise early following surgery, and use
other preventative measures including prophylactic anti-embolic stockings and
anticoagulants. The calf muscles, by contracting and relaxing, exert a pump
action on the deep veins, so sitting for prolonged periods without changing
position slows venous return, particularly in the lower legs. Circulation may
be further hindered by the compression of the popliteal vein against the edge
of the seat. Venous flow velocity has been shown to be two-thirds less sitting
than if supine4.
Although
the term economy class syndrome was first coined by Cruickshank and colleagues4
and has recently been widely used by the media, based on the theory that a
cramped seated position is a significant factor in the development of DVT and
PE, travellers’ thrombosis can also occur in first or business class5. Equally,
the risk of DVT can be associated with other forms of transport where prolonged
immobility occurs, such as during train, car and coach journeys6. The House of
Lords Select Committee recommended that health care professionals and others
should stop using the misleading term economy class syndrome but instead use
flight-related DVT or travellers’ thrombosis1.
Signs
and symptoms
Small
blood clots, which may be reabsorbed by the body, do not necessarily result in
any signs or symptoms. However if the blood clot enlarges it can cause pain
and/or swelling of the leg, increased tenderness, redness and warmth during
travel or even several days afterwards. DVTs are not dangerous but
complications can arise. If part of the blood clot breaks off it can travel in
the circulatory system and block a blood vessel resulting in an embolus. One
per cent of all people with DVT develop a PE7. While this event is rare it can
be life threatening.
Incidence
As
highlighted by the House of Lords’ Select Committee report, the true incidence
of travellers’ thrombosis is unknown and further research is required1. The
incidence of deep vein thrombosis in the general population below the age of 40
years is thought to be 1 per 3000 per annum8 with the incidence rate increasing
with age.
Research
findings
It
is not only immobilisation that is a risk factor for deep vein thrombosis but
also a prolonged seated position. In 1940, Dr Keith Simpson, a London
pathologist reported a six-fold increase in people dying as a result of DVTs
travelling to their lungs during the blackouts of the Second World War. They
occurred in people who sat in crowded air raid shelters on deck-chairs, with the
popliteal vein obstructed against the wooden slat of the chair. The problem was
resolved with the introduction of sleeping bunks.
Since
1940 there have been several case reports of people experiencing DVT and PE
following long haul travel, including Homans in 1954 who identified two cases
of DVT9. Since then there have been over 250 published cases of DVT thought to
be associated with travel.
Unfortunately
most of the early reports recorded single or small numbers of cases. There have
been only a few case control studies to investigate any association between
travel and the development of a DVT. However, the findings do not appear to
correlate.
Ferrari
and colleagues’ case control study conducted in a cardiac unit in a French
hospital located close to an international airport found that a history of
recent air travel occurred in 39 subjects (24.5 per cent) in the DVT group,
compared to 12 cases (7.5 per cent) in the control group.
History
of travel occurred almost four times more frequently in the DVT group (odds
ratio of 3.98)6, but the incidence of DVT was higher in subjects who had a
recent history of car travel (28 cases) than train (2 cases) and air travel (9
cases). The mean duration of travel was 5.4 hours.
Kraaijenhagen
and co-workers’ study included a cohort
of 1,911 patients, of which 463 (24 per cent) were diagnosed with DVT.
Thirty
two patients with DVT were compared to 104 controls where suspected DVT had
been ruled out. A history of prolonged travel by air, car, bus, train or boat
of more than three continuous hours was investigated. Mean duration of travel
was found to be longer than seven hours. As only four of the DVT patients were
found to have a history of travel compared to 13 of the patients without DVT,
no correlation was found between travel and DVT.
It
could be argued that not all confounding factors were controlled, as it is
possible that patients who had travelled had developed clots which may have
spontaneously lysed and therefore they could have been assigned to the control
group. It could also be argued that Ferrari et al6 might have introduced
referral bias by having a prior knowledge of a history of recent long-distance
travel in the cases.
A
large retrospective study was conducted in the north of England over a 12-month
period in five hospitals serving a relatively fixed population of 650,000.
All
patients with DVT were asked whether they had travelled in the four weeks prior
to diagnosis. It was found that only 24 cases were identified out of a total of
634 cases giving an incidence of 0.4 per 10,00010. It is thought that the
incidence of DVT in air travellers is small and therefore large prospective
case control studies are required to examine symptomatic travellers for the
development of travellers’ thrombosis.
Risk
factors
Various
risk factors have been recognised for DVT from studies on surgical patients.
Preventive
measures
There
is little research regarding preventive measures for travellers’ thrombosis.
Recently Scurr et al conducted a small randomised prospective control study to
look at the efficacy of using graduated compression stockings for air
travellers11. The study included 200 passengers over the age of 50 who were
flying long haul with a flight duration of at least eight hours. Blood
screening, including for factor V Leiden deficiency, D-dimers and, where
appropriate, thombophilia screens and venous ultrasonography were conducted
both before and after travel.
One
group wore below-knee graduated elastic compression stockings, the other group
did not. Twelve passengers who did not wear the stockings developed signs of
DVT but were asymptomatic. No passengers who wore the stockings developed a
venous clot. However, four of the passengers who wore stockings developed superficial thrombophlebitis. While the
findings appear to support the case for compression stockings, not all
confounding factors were controlled, such as delays in taking D-dimers
resulting in negative results but positive ultrasonography. It could also be
argued that diagnosis of DVT was not confirmed by venography even though
D-dimers were negative. The incidence of DVT was high in the study (10 per
cent). It could also be argued that while the study design tried to eradicate
bias, the technicians carrying out ultrasonography may have been influenced by
patients discussing their experience of the flight including whether or not
they wore stockings. Subjects were also over the age of 50 and therefore their
age would put them at higher risk.
The
findings did not indicate any incidence of serious complications.
Both
Virgin Atlantic Airways and British Airways have special assistance departments
who are able to advise health professionals and passengers on fitness to fly.
Use
of aspirin
The
use of aspirin is controversial. Aspirin has been used as a preventive measure
for heart attacks. However, further research is required to show if any
benefits can be derived for prevention of DVT. It is also important to note
that some people who take aspirin will have a gastric bleed or allergic
reaction.
As
with any medication, the person should be made aware of possible side effects
and contra-indications before use.
Exercise
equipment
There
are many pieces of equipment that have recently been designed to encourage
people to exercise during a flight. The use of such equipment is up to the
individual.
Gentle
exercises to increase circulation can be carried out in the seat. The majority
of airlines display appropriate exercises either in in-flight magazines, in
passenger health leaflets or on in-flight entertainment systems.
Post-travel
It
is important to inform travellers that if they do develop swollen, painful legs
or breathing difficulties after a long journey they should see a local doctor
as a matter of urgency.
Future
research
It
has been recognised by the House of Lords and the World Health Organisation
that further research is required on the incidence of travellers’
thrombosis, the risk factors,
preventative measures and whether there is anything intrinsic to air travel
that increases the risk of DVT.
Researchers
in Australia are trying to acquire funding from the Australian government to
set up a multicentre case control study involving 1,600 DVT cases and 1,600
matched controls, aiming at testing all modes of transport and the incidence of
travellers’ thrombosis.
The
World Health Organisation, in collaboration with airlines through IATA, is also
addressing the issue of research. Study protocols are currently being
developed. The UK Government, through the Department of Health, the Department
of Transport, local government and the regions have set up an interdepartmental
Aviation Health Working Group to oversee further research and to provide advice
to air travellers and the airline industry.
Summary
It
is important that travel health advice does not concentrate solely on the
health risks while abroad but also includes advice on the health risks
associated with the journey. With the correct advice occupational health
practitioners can play a significant role in advising their business travellers
about the prevention of travellers’ thrombosis.
Hazel
Cullinane, a former OH manager at Virgin Atlantic, now works with BUPA
References
1.
House of Lords (1999-2000) Fifth Report, Select Committee on Science and
Technology, London: Stationary Office.
2.
CAA (1999) Passengers at Gatwick, Heathrow and Manchester Airports in 1998
(CAP703), CAA.
3.
Henriksen O (1976) Local nervous mechanism in regulation of blood flow in human
subcutaneous tissue. Acta Physiologica Scandinavica, 97:385-391.
4.
Cruickshank JN, Gorlin R, Jennett R
(1988) Air travel and thrombotic episodes. The economy class syndrome. Lancet ,
27: 497-498.
5.
Ernsting J, Nicholson AN, Rainford DJ (1999) Aviation medicine, 661.
Butterworth Heinemann.
6.
Ferrari E, Chevallier T, Chapelier A, et al (1999) Travel as a risk factor for
venous thromboembolic disease. A case study. Chest, 115: 440-444.
7.
Kakkar VV et al (1975) Lancet, ii: 45-51.
8.
Anderson F A et al (1991) Archives of .Internal Medicine, 151(5): 933-938.
9.
Homans J (1954) Thrombosis of the leg veins due to prolonged sitting. New
England Journal of Medicine, 250:148-149.
10.
Kesteven PLJ (2000) Travellers thrombosis. Thorax 55(Suppl 1): S32-S36.
11.Scurr
JH, Machin SJ, Baile-King, Mackie IJ, McDonald S & Smith PD (2001)
Frequency and prevention of symptomless deep-vein thrombosis in long-haul
flights: a randomised trial. Lancet, 357:9267.
Useful
websites
Health
Advice to Travellers: www.doh.gov.uk/traveladvice/
Department
of Health website: www.doh.gov.uk
FCO
website: www.fco.gov.uk/travel/
Know
before you go: www.fco.gov.uk/knowbeforeyougo
British
Airways: www.britishairways.com/health/
Virgin
Atlantic: www.virgin-atlantic.com/
Risk
factors
–
People over 40 years of age
–
People with a history of DVT/PE or strong family history
–
Women who are pregnant or have had baby in the last six weeks
–
Previous or current history of malignant disease, heart failure or circulation
problems or who have undergone recent surgery or have injured the lower limbs
–
People with a current or previous history of a blood disorder that affects
blood clotting such as Factor V Leiden deficiency
–
People who are dehydrated
–
Women taking the contraceptive pill
–
There is some debate as to whether obesity or current tobacco smoking are
significant risk factors for DVT
Preventive
measures
All
passengers should:
–
Avoid dehydration by limiting alcohol and caffeine-containing drinks prior to
and during the flight and drink plenty of non-alcoholic drinks
–
Exercise calf muscles by pumping feet on the floor either standing or sitting
every 30 minutes during the journey
–
Take short walks around the aircraft when safe to do so, ie when seat belt
signs are off, or around the departure lounge if flight is severely delayed
–
Avoid sitting with legs crossed, ideally sit with feet flat on the floor or
supported by a footrest
–
Ideally avoid taking sleeping tablets
–
Breathe deeply to help improve circulation
Passengers
with predisposing factors should also:
–
Consider wearing compression stockings, measured and fitted correctly, before they
fly
If
passengers have:
–
A previous or current history of clotting disorders
–
A family history of clotting conditions
–
A history of cancer
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–
Had recent major surgery
–
Had a recent stroke they should consult their doctor regarding
their fitness to fly and the possible use of a prophylactic anti-coagulant such
as low molecular heparin
