Contents

This page explains about DVT and Economy class syndrome. Either scroll down as you read or click on the titles below to go straight to that subject:

1. What is deep vein thrombosis?
2. Why does DVT happen?
3. What problems can DVT cause?
4. What are the possible early problems from DVT?
5. What are the possible late problems from DVT?
6. What about DVT following plane flights? (Economy class syndrome)

Deep Vein Thrombosis (DVT)

What is Deep Vein Thrombosis?

The heart pumps blood around the body. The arteries take blood from the heart to the places it is needed and the veins take it back to the heart.

There are two major sets of veins in the body, the deep veins which are deep inside the muscles and the surface (superficial) veins which are the ones which you can see under the skin and which sometimes form varicose veins. The deep veins are larger and more important than the surface ones. A deep vein thrombosis is a blood clot occurring in one of the deep veins, most commonly in one of the leg veins.

Why does DVT happen?

It is very important that blood does clot when necessary, otherwise even a small cut would lead to serious loss of blood. On the other hand, if blood clots in the wrong place this too can cause serious problems. It has been known for about 150 years that there are three main things that increase the chance of a blood clot forming.

1. Damage to the veins themselves; (for example, breaking a leg may damage the veins in the leg);
2. Increased "stickiness" of the blood; (for example, dehydration increases the tendency of blood to clot, so does pregnancy and injury. Some medical conditions also make blood clots more common, for example some types of cancer, some people have abnormalities of the clotting systems themselves which make clotting more likely;
3. Decreased blood flow through the veins. The main thing that makes blood flow through the veins is using the muscles around the veins. If you are immobile, for example after an illness or an operation then you are at increased risk of a clot.

Often several of these factors come together, for example if you break a leg you may damage the veins, have increased stickiness of the blood because of your injury and be immobile because it hurts to use the muscles of the leg.

What problems can DVT cause?

As methods of detecting DVTs improve it has been realised that minor clots are much commoner than was once thought and that many of them never cause any trouble and are reabsorbed by the body with no long term effects, the person who has the clot may experience no symptoms at all and not know that they have had one. Probably many DVTs cause no problems whatsoever.

If DVTs do cause problems then there are two main areas to consider early problems and late problems.

What are the possible early problems from DVT?

I: Problems in the leg

A DVT causes inflammation. This may make the leg feel hot, tender and swollen and look red. This is not particularly reliable as some DVTs cause no trouble and other things, for example, an infection can also cause inflammation and produce a similar picture.

In general the bigger and further up the leg the DVT is the more obvious is the effect on the leg. Sometimes some of the blood clot in the vein can be dislodged and be carried up with the blood returning to the heart to the lung. This is the cause of the second major area, problems in the lung.

II: Problems in the lungs

If a bit of clot breaks off from the leg veins and gets carried up to the blood vessels of the lung it is known as a pulmonary embolus or PE. The effect of this depends on how big the clot is and how many of them there are. A single small PE may cause no symptoms at all. As the amount of clot gets bigger it may cause shortness of breath and pain on breathing and sometimes coughing up blood. A massive PE may block the circulation completely and stop the heart from being able to pump blood around the body causing sudden death.

What are the possible late problems from DVT?

Some people have no long term effects from DVT.

The main potential long term problems from DVT are caused by the effects of the clot on the veins in the leg. In the early stages, the veins may be blocked by the clot, making the leg swell up. Usually, the body reabsorbs some of the clot which unblocks the vein.

However, when you are standing up, blood has to flow uphill from the legs to get back to the heart. To do this it relies on one way valves in the veins. When you walk, the muscles squeeze the veins, pushing blood upwards. When they relax, the one way valves stop the blood coming back down.

The effect of this is to work as a pump pushing blood upwards to the heart. A DVT can permanently destroy some or all of the one way valves in the legs stopping the pump from working properly. As a result there is a permanently high pressure in the veins in the leg which causes the leg to swell and damages the skin. In the early stages this shows as a brownish colour in the skin around the ankle, later on this may progress to ulceration.

What about DVT following plane flights? (Economy class syndrome)

Recently, there has been a lot of publicity about people having venous thrombosis after travelling, particularly after plane flights. In fact there is nothing new about this. If you are immobile for long periods this increases the risk of DVT, similarly if you are dehydrated this also increases the risk (See ankle picture above).

Both immobility and dehydration can occur on long journeys. There is probably nothing special about aeroplane travel itself. For example, you could just as easily get a DVT on a long coach journey. Although DVT can occur on plane flights, it is rare for people to develop blood clots which cause trouble or spread to the lung after a flight. You do not need to cancel your holiday! However there are some simple things that can be done to reduce the risk:

1. Keep mobile. Make sure you move your ankles and legs to get the leg muscles working and pump blood through the veins. Stand up and stretch or go for a walk up the aisle from time to time;
2. Wear some "flight stockings". These increase the speed of flow through the deep veins and help reduce the chances of a clot. It is important that they fit well and are comfortable. They only need to come up to the knee not the whole of the leg;
3. Avoid dehydration. The air is very dry at altitude and it is easy to get dehydrated without recognising it. Drink plenty of water. Go easy on the duty free booze as this tends to cause dehydration;
4. Aspirin? Taking 75mg (a quarter of a normal 300mg tablet) some hours before your flight may reduce your chances of a DVT slightly (but remember that Aspirin can sometimes cause indigestion in people with a tendency to it, if in doubt ask your GP);
5. Special cases. For most people the risk of a DVT is extremely small and the common sense precautions above reduce it still further. A few people are at especially high risk, for example if they have had lots of blood clots already or if they have an abnormal clotting system. If you are one of these it would be sensible to obtain specialist advice prior to flying. You might benefit from covering the journey with injections of low molecular weight Heparin.