What Are They?
Deep vein clots, or DVTs, are clots occurring usually in the legs in the deep muscle-encased veins in the calf to thigh area, but spreading to, or involving, the veins in the pelvic and abdomen area. This restricts the main passage of blood back to the heart, although there are usually other veins still open. Consequently there may be some swelling of the affected limb. This may not occur if there are sufficient efficient collateral veins functioning. The more serious problem is that the clot may continue to grow and a piece break off and pass up the circulation, through the heart and lodge in the lungs either partially or completely blocking circulation of the arterial blood to the lungs. More complete blockages can result in sudden death. Smaller ones can cause shortness of breath and chest discomfort.
What Are The Causes?
Clotting of the blood is more likely to occur in situations where there is slowing of flow such as caused by increased viscosity of the blood, turbulent flow and restriction of flow, and with an underlying predisposition to clots. A number of conditions are associated with an increased risk of clots:
- Oral Contraceptive Pills
- Surgery and trauma
- Malignancies i.e. cancers
- Varicose veins
- Certain predisposed blood conditions (Factor V Leiden - the commonest, resulting in a resistance to the natural anticoagulant activated protein C -, deficiencies in protein C, protein S, antithrombin III, and disorders of plasminogen)
- Immobility at a job or in convalescence
What Is Economy Class Syndrome?
There has been a reported increased incidence of deep vein clots and some subsequent deaths occurring around flying. Studies have been undertaken to determine the real incidence and risk. They revealed a higher than expected incidence of asymptomatic deep vein clots in people flying for five hours or more. People who wore grade I below-knee support stockings had a much lower incidence of the clots. Surgical and other procedures within a month of a five-hour-plus flight increased risks (this is in people without support hosiery). There is a concern that the relatively cramped conditions that occur in economy class seats could predispose people to a higher risk than those in roomier seats. The problem is not exclusive to flying. Long coach and car journeys can also give rise to the same problems. In World War II a number of people suffered sudden death while sheltering in the Underground in London during air raids. They would be sitting for hours dosing in sitting positions in deck chairs – it became known as the Elephant and Castle effect, named after one of the subway stations. Three factors contribute to changes that predispose to DVTs:
Prolonged immobility and this with the knees bent and feet low with the sitting position. Blood accumulates in the lower limb and sluggishly moves back to the heart.
Relative dehydration from both air-conditioning and alcohol intake without sufficient fluid replacement. This affects the blood concentration of cell constituents that can predispose to clotting.
The changes that occur with the low-pressure aircraft cabin. Aeroplanes are pressurised to about 8-10,000 feet (3,000m) in normal flight. The skin in the legs is therefore subject to less external pressure, which allows water in the legs to redistribute from the blood vessels into the tissue fluid about the cells. This causes a relative increased concentration of blood in the blood vessels, which is a risk factor for clotting. With due fluid intake this is usually compensated for.
What Can Be Done To Prevent It?
A number of things will help.
- A good fluid intake of water, juice and non-alcoholic beverages will replace lost and redistributed fluid.
- Moving the legs regularly throughout the flight, half hourly to hourly, will pump extra blood from the limbs back to the heart. Walking is ideal but may well not be practicable. Rocking the feet up and down and turning them in circles about the ankle is ideal. Many airlines now provide information on such exercises as part of their initial welcome or on specific channels of their entertainment systems.
- Wearing some graduated compression stockings throughout the flight. These can be obtained in a number of different types. The knee high type socks are normally sufficient. They need to be properly fitted for your size. Graduated compression types are important to ensure the pressure encourages the blood to return to the heart, rather than constricting flow in the limb. The Class I type is fine for otherwise healthy people. These have a pressure of 18-22mmHg at the ankle. People with fluid retention, vein or other problems in normal life, would benefit from wearing Class II (25-32mmHg ankle pressure) or higher if necessary. Note that different companies can rate the classes of their stockings differently from others. There is supposed to be some universal agreement on standards though.
- Half an aspirin daily for day before and of flight(s). This is contraindicated in people with allergies to aspirin, salicylates, non-steroidal medications, haemophilia, active peptic ulcers and previous bleeds with aspirin-like compounds (may be possible to use enteric coated version) and caution needs to be exercised if people have asthma.
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