Preventing deep vein thrombosis (DVT)


1000 patients suffer a DVT each year in the UK. A clot forms in the large veins deep inside the leg causing swelling and pain. One in 10 of these clots will break off and spread to the lungs where it is called a pulmonary embolus. A pulmonary embolus can result in chest pain and breathlessness and can be fatal. Some patients suffer from a pulmonary embolus without any obvious signs of a DVT.


DVTs can occur for many reasons, but in this blog I want to discuss DVTs that arise following operations. An operation can cause a DVT because the patient is immobile. Normally as we walk around the muscles in the calves of the legs squeeze the veins forcing blood back to the heart. Under general anaesthesia there is no movement and the blood slows down. Once the blood is stationary clots can form.


Each operation carries a specific risk of a DVT. Multiple operations therefore increase the risk. Flying in a commercial aircraft as a passenger also carries a risk of DVT because the cabin is depressurised to about 8000 feet and this causes dehydration so that the blood in the legs becomes thicker. Combined with immobility especially in economy class DVT is a possibility. It is very important to try and avoid not only multiple operations but also flights immediately before and after an operation although we think it may be about three months before the risk level returns to normal. Many of my patients, who come from all over the world, cannot arrive in the UK three months before nor remain for three months after an operation.


All my patients are assessed for the risk of DVT. We look for the following risk factors:

  • multiple operations and or flights and or pregnancy
  • surgery of more than 30 minutes
  • patients over the age of 40
  • obesity
  • smoking
  • a family history of DVT
  • cancer
  • inflammatory diseases
  • the combined oral contraceptive
  • dehydration
  • a history of bed rest or inactivity
  • recent damage to the legs or varicose veins
  • heart disease
  • hepatitis
  • rheumatoid arthritis
  • specific conditions such as thrombophilia, anti-phospholipid disease, FVLeiden MTHFR C677T, A1298C, PAI-1 4G/5G, or Prothrombin 20210

Clearly there are some risk factors we can’t change but others we can and in particular smoking.


Turning to prevention, we tried to mobilise patients as soon as possible and this is one reason why we do not allow patients to stay in bed and we try to resist patients staying in hospital for an extra day or two ‘just in case’. For operations over 30 minutes patients are given antiembolism stockings to wear. If the patient is anaesthetised, we also use inflatable boots which use an air compressor to intermittently squeeze the calves imitating the effect of walking. We can prevent dehydration with intravenous fluids and strict adherence to the nil by mouth policies to ensure that all patients drink until just two hours before anaesthesia.


For high-risk patients we also use anticoagulants although this will depend on balancing the risk of a DVT against the risk of bleeding. We tend not to use anticoagulants for example after breast surgery or cosmetic surgery but at the end of the day it is a careful decision made between surgeon and anaesthetist and one that is taken on every single patient at the final checklist before we start an operation.


Historically we always used to use heparin if anticoagulants were indicated, which had to be given by injection several times a day. New forms of heparin called low molecular weight heparin can be given once a day using a pre-filled syringe but we know many patients do not finish the course because of the discomfort of administration. I therefore only tend to use heparin for the immediate post-operative period because unlike other anticoagulants we have an efficient antidote; if the patient bleeds while still in hospital we can reverse the heparin and normalise the clotting.


For operations where bleeding is unlikely and for preventing deep vein thrombosis in higher risk patients when they leave hospital we have used warfarin which is a tablet that needs to be monitored with regular blood tests. This is very inconvenient especially when a patient has had an operation or may be immobile and I now use a drug called dabigatran, a tablet that does not need monitoring and can be taken once a day. Dabigatran has been widely used for cardiac conditions such as atrial fibrillation and its risk profile is as good as warfarin. Due to the way the regulators work, it is only licensed in the UK for certain operations but the mechanism by which a DVT arises after an operation is the same regardless of the operation and therefore I consider it a safe and preferable alternative


If patients are flying soon after an operation my recommendation is always to take home their antiembolism stockings and wear them from the morning they get on the aircraft ideally until the following morning. Two adult aspirin or 600 mg will also prevent platelet stickiness which is how clots form and this effect lasts for 7 to 10 days so one dose on the morning of the flight if there is no contraindication is something I regularly do even though I have not had an operation. If you are already taking a low dose aspirin, so called baby aspirin, then this has the same effect. I often also give my patients a dose of low molecular weight heparin to administer on the day of the flight and this is the recommendation for patients who are at high risk such as those with genetic pre-disposition to DVT although if the patient is flying frequently over a period of time dabigatran is an alternative


All patients who are on any form of anticoagulation should be aware of the risk of spontaneous bleeding. Indigestion should be considered as a possible sign and medical help obtained the same day. Other signs of bleeding into the guts include constipation and very dark stools. Bleeding can rarely occur in the brain so any weakness of the limbs, visual issues or other signs of a stroke also demand immediate medical attention. However in practice I have never had a patient who has come to harm.