Causes of VTE

DVT - Deep Vein Thrombosis - is the name given to the clotting of blood in the deep veins of the leg.

There are 3 main factors than cause DVT. These 3 factors were first described by Virchow - and are therefore known as Virchow's Triad.

Virchow's Triad

1. Changes in blood flow
2. Changes in blood constituents
3. Changes in the vein wall

The understanding of these factors lets us understand vein thrombosis and economy class syndrome - and help us understand how help to prevent it.

1. Changes in blood flow

This is explained in the following pages. Changes in the blood flow in the veins in the legs is the most important factor that we can influence, to reduce the risks of DVT (economy-class syndrome).

2. Changes in blood constituents

Things that make the blood thicker and therefore less able to flow easily, or more "sticky" and thus more likely to clot, increase the risks of DVT. There are some factors that can be changed and some that cannot:

Cannot be changed - Your genetics ie: Factor V Leiden, Protein S or C deficiencies.

Can be changed - Dehydration, Oestrogen (the pill and maybe HRT), Varicose veins, Smoking.

Cannot be changed

If you genetically have a tendency to from clots in your veins, you are said to have "Thrombophilia" - literally "Thrombus (or blood clot) liking". Blood tests can tell whether you are one of those people at higher risk of DVT - it is estimated that up to 1 in 3 of the population may have a mild or moderate "Thrombophilia".

Can be changed

Dehydration - You can become dehydrated if you don't drink enough water or fruit juice, or conversely if you drink too much tea, coffee or alcohol. Caffeine in tea and coffee makes you pass more urine (an effect called diuresis) and alcohol acts in a similar way. This results in the blood becoming thicker and more likely to clot.

Oestrogen - The oral contaceptive pill is known to increase the risks of DVT. There is some debate as to whether HRT has a small effect on venous clotting.

Varicose veins - Varicose veins cause a pump failure of the legs and disordered flow. This can cause clots in the varicose veins themselves (superficial thrombophlebitis) or in the deep veins - DVT.

Smoking - Smoking activates the platelets and also damages the vein wall - thus smoking increases the risks of clots in the arteries and there is some evidence that it also increases the risks of DVT.

3. Changes in the Vessel Wall

The vein wall can be damaged or affected by smoking or local pressure pushing on the leg.