Medsafe, a business unit of New Zealand's Ministry of Health, also provides useful information and recommendations.

The Traveler's Thrombosis is a thrombosis that occurs in the deep venous system of the lower extremities (with or without pulmonary embolism complications) of a person, who did not show any signs of acute venous embolism at the time of departure, resulting from a prolonged seating during flights. The Traveler's Thrombosis is also known as "deep vein thrombosis" or DVT.

Causing Factors

The low mobility fostered by long-haul flights favors the developments of deep vein thrombosis in patients with existing risk factors. Causing factors in the development of thrombosis are:

pressure on the upper thighs, caused by prolonged sitting and low mobility in narrow seats and rows;

low air humidity on board can favor the formation of blood clots in cases where passenger may be lacking fluids.

Category 1 - low risk

Every prolonged seating period during long-haul flights may present a low risk for passengers.

Category 2 - moderate risk

In addition to a prolonged flight duration,

Pregnancy or post-natal period

or at least two of the following factors:

• be aged 60 years and over
• clinically relevant heart diseases
• presence of vascular diseases in the family / susceptibility to vein affections
• large varicose veins, chronical venous insufficiency
• ovulation suppressors (birth control pill)/ post-menopausal, hormone replacement therapy.
• obesity (BMI>30)
• exsiccosis

Category 3 - high risk

In addition to a prolonged flight duration,

• venous thromboembolism antecedents
• malignant tumors or other serious diseases of the sort
• leg injuries requiring the immobilization of the limb
• recovery from an operation involving a high risk of thrombosis

General measures:

• exercises - stretch legs and change position frequently (e.g. scissors and other isometric exercises/if possible, walk a few steps)
• abundant intake of fluids (avoid excessive alcohol intake)
• moderate use of sedatives and hypnotic pills

Category 2 - moderate risk

In addition to the general measures (see category 1),

• compression stockings (compression class I). 
• For passengers with venous insufficiency, it is advisable to wear the appropriate calf-length compression stockings.
• in special cases, such as pregnancy, consider use of low molecular weight heparin

(see category 3).

Categrory 3 - high risk

In addition to the general measures (see category 1) and compression stockings (see category 2), consider use of low molecular weight heparin as follows:

• subcutaneous application right before departing
• once daily for round trips
• before each trip presenting a high risk of thrombosis (see risk categories)

Abundant intake of mineral water, still water, soft drinks, herbal tea are recommended. An additional 1 to 2 litres is advisable, depending on the flight duration! Avoid excessive intake of coffee, black tea, and alcohol as these drinks have a dehydrating effect.

Exercise on board - Exercises generally activate the muscle pump, which accelerates the flow of blood in the veins. Wear clothing that is loose and comfortable to avoid the restriction of the blood flow. Do isometric exercises. While sitting, carry out circling and jiggling leg exercises. From time to time, take exercises for the leg muscles, like tensing and relaxing the lower and upper thigh muscles. Massage legs.

Compression stocking of the category 1-2 are recommended, even in the case of a low risk for thrombosis. Most of the time, knee-socks are sufficient. Please consider that expert advise is absolutely necessary. Material of poor quality or bad fitting in the back of the knee together with folds are unsuitable! Depending on the medical condition, calf socks of different categories are recommendable.

Medication improving blood flow - Usually, low molecular heparin can be subcutaneously injected to the fat tissue of the abdominal wall or upper thigh. The passenger has to learn from the doctor how to self-inject and should also eb aware of the side effects and contra-indications.

Additionnal information is provided on all Austrian Airlines long-haul flight via a video tape featuring fitness tips and an accompanying announcement.