Venous Thrombosis, Phlebitis &
Post Thrombotic Syndrome (PTS)
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Thrombosis, Phlebitis
When a blood clot forms in a vein, it is called a thrombosis. In principle there are three reasons for developing a thrombosis;

1. The blood is abnormal and more likely to clot (thick blood)
2. The vein lining is abnormal, and doesn't stop clotting from occurring (abnormal vein)
3. The flow of the blood through the veins is reduced (stagnant blood clots).

The following factors are linked to thrombosis

Immobility Pregnancy and some hormonal drugs
Dehydration Previous thrombosis
Varicose veins Trauma/Injury/Recent Surgery
Obesity Increasing Age
Blood disorders Cancer

There has been a lot of interest in the risks of thrombosis during long distance flights recently leading to a lot of anxiety. There is a shortage of scientific facts here so it is difficult to be precise about the risk. The risk has probably been overstated but does exist. The sensible approach is to take reasonable precautions but it is not necessary to avoid flying unless your medical advisor specifically recommends this course of action.

Keep yourself well hydrated during the flight, do what exercises you can (ankle movements in particular), wear loose clothing but firmer support type stockings, and take a small dose of aspirin (75mgs) if you are able to.
If the deep veins develop a thrombosis (clot) this is called a DVT (Deep Vein Thrombosis). This causes the leg to swell and become painful. It is important to have this correctly diagnosed since treatment to stop the clot enlarging may be necessary, which involves thinning the blood with heparin and warfarin. The deep veins of the leg may be damaged by the thrombosis and fail to work normally after a DVT. Wearing support stockings after a DVT has been shown to reduce this problem.
A thrombosis in the superficial, "surface", veins leads to phlebitis. The affected vein(s) become inflamed (red), swollen, hard and painful. The condition usually resolves over 4 - 8 weeks. Painkillers, a supportive bandage or tubigrip may help. If it is severe and extensive seek medical advice.
After a DVT the clot in the veins of the leg can be broken down over 3-6 months to restore patency and flow in the vein. Sometimes the clot remains as a blockage in the vein. Even a patent vein is usually damaged after a DVT and does not function normally. Overall this reduction in vein function can lead to the following symptoms and signs

1. Swelling of the leg.
2. Enlarged surface veins
3. Pain and heaviness in the leg.
4. Skin colour change, redness or a brown pigmentation.
5. Hardening of the tissues of the leg at the ankle and low calf.
6. Leg ulceration

These changes are referred to as Post Thrombotic Syndrome (PTS). Depending on how many features are present and how severe the PTS is graded as mild, moderate or severe. Mild PTS is common after DVT (50%) moderate to severe forms less so (10%).

Wearing support "compression" stocking on the leg after DVT for at least 1 year and upto 2 years can reduce the amount of PTS that develops after a DVT. Keeping mobile and avoiding weight gain will also help. A further DVT in the same leg increases the risk of PTS significantly so it is important to avoid this, anti coagulation helps.

It is difficult to repair the veins after a DVT so treating PTS once it is established is difficult. Prevention is therefore very important. There is a lot of interest in drugs to "dissolve" the clot when the DVT first occurs (thrombolysis) as a potential way to prevent PTS. Trials are underway to see how effective this is. The risk with lysis is bleeding, so it is a treatment that needs to be done very carefully in hospitals. We need to be sure that keeping people in hospital for this treatment after a DVT is safe and effective before using it routinely after DVT.