Environmental Engineering Reference
In-Depth Information
although many other risk factors are known (see Table 4.1); but, as yet, the magni-
tude and independence of each risk factor is uncertain. The thrombosis can either
partially or completely block the flow of blood in the vein, which in many cases causes
no ill effects. However, there can be serious complications - most notably, formation
of a pulmonary embolism. A pulmonary embolism can occur when the blood clot
breaks free from the vein wall and travels to the lung, where it blocks an artery with
potentially life-threatening consequences and requires immediate medical attention.
Ta b l e 4 . 1
Reported risk factors for the development of DVT
Patient-related risk factors
Cabin-related risk factors
Blood disorders affecting clotting tendency -
thrombophilia
Flight duration or frequency of travel
Impairment of blood clotting mechanism, such as
genetic clotting-factor abnormalities factor V
Lieden
2
and prothrombin G20210A; these may
explain up to 25% of all thrombotic events
Prolonged immobilization, especially in a
seated position (particularly cross-legged)
Cardiovascular disease
Coach position
Presence of malignancy
Low air pressure
Recent trauma to lower limbs or abdomen
(previous six weeks)
Relative hypoxia
Personal or family history of thrombosis
Low humidity
Recent minor surgery (previous three days) and
major surgery (particularly leg surgery)
Dehydration - depletion of body fluids
causing increased blood viscosity
Pregnancy or puerperium (the period from birth
to the first six weeks postpartum)
Women on oestrogen hormone replacement
therapy, or oral contraceptives
Increasing age above 40 years
Obesity
Smoking
Varicose veins
Source:
Arfvidsson et al, 2000; Kesteven and Robinson, 2001
While DVT events have been recognized in many modes of transport, air travel is
most typically associated with situations where the passenger is in a restricted posi-
tion (ie immobilized for prolonged periods, such as on long-haul flights). Because of
the 'cramped' seating arrangements associated with economy-class air travel, DVT
was alternatively termed 'economy class syndrome' (Symington and Stack, 1977).
However, many experts believe this to be a misconceived term suggesting the possi-
bility that first and business class travellers need not concern themselves with the pos-
sibility of DVT, and the more appropriate term 'traveller's thrombosis' is now preferred
(House of Lords, 2000).
