Printable advice sheet
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Information on DVT
Blood clotting is an essential protection against severe loss of blood from injury to veins or arteries. But blood is only supposed to clot when it is outside a blood vessel. Clotting within an artery or vein is always abnormal and is often dangerous.
The word ‘thrombosis' means clotting of blood within an artery or a vein. A deep vein thrombosis (DVT) is a clot occurring in the large veins of the legs that lie in amongst the muscles. There is another set of veins lying just under the skin.
In a deep vein thrombosis, a long, soft, snaky blood clot forms, usually attached at one end. It may become very large before it breaks loose into the bloodstream. If it does come loose, it will be carried quickly by the movement of blood into the larger leg veins. From there it will be carried up into the largest vein of the body and into the right side of the heart, then into the main branches of the arteries to the lung, where it will impact, blocking the blood flow. This is called pulmonary embolism or PE and is a common cause of sudden, unexpected death. When PE is severe it causes the lungs to collapse and heart failure.
Blood clots in superficial veins in the legs below the knee (phlebitis) are much less serious and usually easily treated with drugs.
You may get swelling, pain, tenderness and redness especially at the back of the leg below the knee. DVT usually, though not always, affects only one leg.
The pain may be made worse by bending the foot upward towards the knee. In some cases there may be no signs or symptoms of DVT at all in the legs and problems only become obvious when a pulmonary embolus or PE develops from the clots in the legs. Fortunately PE is rare. PE can cause breathlessness, chest pain and in severe cases, collapse. Both DVT and PE, whatever the cause, are serious conditions and need urgent investigation and treatment.
The risk of DVT and PE is greater in people;
- over 40 years of age,
- who have had blood clots already,
- with a family history of blood clots,
- suffering from, or who have had treatment for, cancer,
- with certain blood diseases,
- being treated for heart failure and circulation problems,
- who have had recent surgery especially on the hips or knees; or;
- who have an inherited clotting tendency.
DVT is also more common in women who;
- are pregnant,
- have recently had a baby,
- are taking the contraceptive pill, or,
- are on hormone replacement therapy (HRT).
These groups make up 90 to 95% of all those who get DVT and/or PE.
Deep vein thrombosis can occur in normal veins for no obvious reason, and has been linked with people who are immobile for long periods of time.
There is some evidence that long-haul flights, especially when passengers have little or no exercise, may increase the risk of developing DVT. Experts suggest that the proportion of people who develop DVT because of air travel is small, but the information is limited. It is not easy to decide whether the flight itself caused the DVT or whether people were at risk for other reasons.
While it is difficult to be certain what the exact causes of travel-related DVT are, experts agree that lack of exercise or immobility are major underlying risks. They have also identified that people at increased risk of DVT/PE in general are those more likely to develop travel-related DVT/PE.
Suspected DVT or PE is based on the history and the symptoms and is confirmed by ultrasound scanning or by a special x-ray taken after injecting a dye (contrast medium) that is opaque to X-rays (a venogram).
A more refined form of ultrasound examination called Doppler ultrasound, which can show how fast the blood is flowing in a blood vessel, is often used.
Treatment of DVT and PE is with blood-thinning drugs or anticoagulants, including warfarin and heparin. Aspirin in low doses also acts as a blood thinning drug and is used to prevent clotting conditions in the arteries like coronary thrombosis. Its benefit in preventing DVT is debatable.
A large established deep vein thrombosis is sometimes treated with a drug that can actually dissolve the clot. Clot-dissolving enzymes, such as streptokinase and urokinase, have been in use for many years, but TPA appears to have several major advantages over these earlier drugs.
There have been recent concerns about the effects of cranberry juice on the effectiveness of warfarin. The Committee on Safety of Medicines is is currently reviewing reports, which suggest that cranberry juice acts to increase the potency of warfarin and may therefore increase the risk of haemorrhage. Present advice is to avoid or limit drinking cranberry juice if you are taking warfarin, until the situation has been investigated further.
Avoid immobility, especially after surgery.
People in high risk groups should consult their doctor before they embark upon long distance travel.
During long-distance travel, especially long-haul flights:
- be comfortable in your seat;
- bend and straighten your legs, feet and toes while seated every half-hour or so during the flight;
- press the balls of your feet down hard against the floor or foot-rest to help increase the blood flow in your legs and reduce clotting;
- do upper body and breathing exercises to further improve circulation;
- take occasional short walks, when in-flight advice suggests this is safe;
- take advantage of refuelling stopovers where it may be possible to get off the plane and walk about;
- drink plenty of water;
- wear elastic compression stockings;
- be sensible about alcohol, which in excess leads to dehydration and immobility;
- avoid taking sleeping pills, which also cause immobility.
People known to be prone to deep vein thrombosis or patients at risk of it are given regular injections of a drug called an anticoagulant that can stop the blood from clotting. The drug is based on the natural anticoagulant heparin.
(This information is a summary of information from NHS Direct)