Deep vein thrombosis (DVT) has been recognised as a major health problem by doctors and nurses for several decades. However DVT did not really hit the public imagination until it was described in the media as economy class syndrome. This name followed the death of the young lady who developed a DVT following a long-haul flight and died of a complication of DVT. As with many medical conditions that suddenly have the spotlight thrown on them, a great many people are now very worried about clots in the leg. It would be nice to say there is nothing to worry about in the vast majority these people, but deep vein thrombosis is common enough to warrant most people having a reasonable knowledge about it.
To understand DVT it is essential to have at least a basic understanding of the circulatory system.
The Circulatory System
The heart pumps blood through the arteries to the skin and tissues throughout the body. The blood delivers oxygen and food to these tissues though the arteries and picks up the waste products and returns to the heart through the veins. In order to flow, blood needs to be fluid in the arteries and veins. However when the blood vessels are damaged, such as in an accident or at surgery, it is essential that the body does not completely empty of blood. Massive bleeding from arteries or veins is called haemorrhage and if enough is lost quickly, the person bleeding can die. Therefore nature has equipped us with blood that clots in such circumstances - the clot acting as a cork to stop any further bleeding.
Thrombosis
In some abnormal circumstances, blood can clot whilst it is still in the veins when it really should be flowing. Such clots are called thromboses (a thrombus is the name given to the clot itself). The vein does not like having clot within it and the presence of a thrombus causes an intense inflammation of the vein wall. What affects this has depends on which vein is affected.
Veins in the legs are divided into two main groups. The first are the veins lying in the fat tissue just under the skin. Some of these can be seen by the naked eye but some are a little too deep to be visible. These veins are called the superficial veins of the leg. The veins deep inside the muscle, which pump most of the blood back to the heart, are called the deep veins of the leg.
If blood clots in the superficial veins, the inflammation can be seen on the surface. Patients can see a red line or patch on the skin which is usually very tender and can often be swollen or lumpy. This is called superficial thrombophelbitis - phlebitis meaning inflammation of the veins. Many people think that this tender redness is an infection and often take antibiotics. This rarely has any effect as the cause of the inflammation is the thrombus and not an infection. Therefore the best treatment for superficial thrombophelbitis is aspirin or one of the other anti-inflammatory painkillers. Superficial thrombophelbitis is rarely dangerous, although if severe can extend into the deep veins causing a DVT.
If blood clots in the deep veins, this is a deep vein thrombosis. As the vein is not near the surface there is no local redness or lumpiness. Instead there is a general tenderness of the calf or the thigh, or in severe cases of the whole leg. There is usually swelling of the leg and this is most usually seen at the ankle although the whole leg can be swollen in severe cases. Unlike superficial thrombophelbitis, the thrombosis in the deep veins can move in the bloodstream up through the heart and into the lungs - a condition known as pulmonary embolism. This can cause chest pain and breathlessness and can even cause death. Fortunately not many people who have DVT go on to get pulmonary embolism but because of this risk, we treat people with DVT as soon as we find them. The other main complication of DVT affects people who have had several DVTs over a period of time. The recurrent inflammation in the deep veins can stop the veins working properly and this can be one of the causes of leg ulcers.
Who is at risk of DVT?
Rather than give a list of risk factors, I find it more useful to explain why clots form in veins. It is any easier for patients to understand how certain things can cause deep vein thrombosis.
Over a century ago the German patholgist found that clots form in veins for one of three reasons:
- If the blood changes
- If the vein wall changes
- If the blood flow changes
All of the causes of DVT stem from these. The blood itself is changed by dehydration (the blood gets more concentrated), some drugs (usually the oral contraceptive pill) and by smoking (the chemicals in the cigarette smoke increase certain proteins in the blood making it more sticky). The vein wall can be changed by damage (such as the trauma or surgery to the legs) or chemicals damaging the lining of the veins (the commonest of which are the chemicals in cigarette smoke). Blood flow through the veins is changed in periods of immobility (such as being in bed ill or sitting in a seat for a long period of time).
One other factor that has become important over the last few years has been the realisation that some people are genetically more likely to have venous thromboses than others. This is due to certain abnormalities of the blood or the blood clotting system and so can be thought of as Changes from Normal Blood.
How do I know if I have a DVT or am at risk of a DVT?
The best way of testing for a DVT is a technique called Duplex Ultrasonography. This is a specialised ultrasound examination that is done without any X-rays, needles or injections. Putting gel on the legs only, a vascular specialist then rubs an ultrasound probe over the veins to get a good picture. Duplex ultrasound allows both the flow in the normal veins to be seen as well as any thrombus that might be present.
At the end of the examination, the vascular specialist can tell whether there is any clot present and, if there is, exactly where it is and how extensive it is. Using this detailed information, treatment can be selected.
For those people worried that they may be at risk of deep vein thrombosis, the duplex ultrasound scan can see if there is any underlying abnormality of the veins that main increase the risk of a DVT and also a blood test can check for any genetic predisposition.
Prevention of DVT
The most common risk factor for deep vein thrombosis is immobility. If you are in hospital the doctors and nurses are fully aware of this and use a combination of heparin injections and stockings to thin the blood and keep the flow of blood through the veins as fast as possible. If you are immobile for any other reason, such as taking a long car or aeroplane journey, then the most important prevention factors are to keep well hydrated, to wear properly fitted graduated pressure stockings and to keep your legs moving regularly using a proven device such as the Airogym™.
For more information regarding DVT please look up www.deepveinthrombosis.co.uk and www.economy-class.co.uk
