Preventing blood clots (DVT and pulmonary embolism): in hospital, after surgery and when travelling

A deep vein thrombosis is a blood clot in a vein, usually in the leg. The NHS says the usual symptoms are throbbing pain in one leg, usually in the calf or thigh, swelling in one leg, red, blue or darkened skin around the painful area (which may be harder to see on brown or black skin) and swollen veins. Sometimes the arm is affected, and occasionally the only sign is pain in the lower tummy from a clot in the pelvic veins.

The danger of a DVT is that part of the clot can break away and travel to the lungs. This is a pulmonary embolism, and the NHS says it can be life-threatening and needs treatment straight away. Together the two conditions are called venous thromboembolism, or VTE. NICE uses that term in its guideline on reducing the risk of hospital-acquired DVT and pulmonary embolism.

Prevention matters because the clots are far easier to prevent than to treat. In everyday life the steps are simple, while in hospital they are organised through a structured risk assessment.

The NHS says DVT is more likely if you are over 60, living with overweight or obesity, smoke, have had a DVT before, take HRT, take the combined contraceptive pill or use oestrogen-containing contraception such as the patch or vaginal ring, or have cancer, heart failure, varicose veins, thrombophilia, inflammatory bowel disease or vasculitis.

There are also situations in which the chance goes up for a time. These include staying in or recently leaving hospital, especially if you cannot move around much, having or having had surgery, being confined to bed for 3 days or more, going on a journey of more than 4 hours by plane, car or train, being pregnant or having had a baby in the previous 6 weeks, and dehydration. The NHS adds that sometimes DVT happens for no obvious reason.

NICE guideline NG89 says that all patients should be assessed to identify the risk of VTE and of bleeding. For medical patients and for surgical and trauma patients, the assessment should happen as soon as possible after admission to hospital or by the time of the first consultant review, using a tool published by a national UK body or a professional network.

The key principle is a balance. The guideline says the individual risk of VTE should be weighed against the risk of bleeding when deciding whether to offer medicine to prevent clots, because the same medicines that prevent clots can increase bleeding. Risk is reassessed at the point of consultant review or if the clinical condition changes.

Pregnant women and women who have given birth, had a miscarriage or had a termination of pregnancy in the past 6 weeks are assessed on admission to hospital or a midwife-led unit, and reassessed within 6 hours of giving birth, a miscarriage or a termination.

Depending on the outcome of the assessment, prevention can combine several measures. The NHS says that if you are more likely to get DVT you may be given medicine to prevent it and may also be given compression stockings, which are knee-high elastic socks that help circulation.

NICE says that people who need anti-embolism stockings should have their legs measured and be given the correct size, fitted by staff trained in their use. Stockings should be worn day and night until the person is no longer significantly less mobile than usual, and removed daily for hygiene and so the skin can be checked, particularly over the heels and bony areas. They should be stopped if there is marking, blistering or discolouration, or pain or discomfort, and a compression device can be offered instead if suitable.

Stockings are not suitable for everyone. NICE lists suspected or proven peripheral arterial disease, peripheral neuropathy or other sensory impairment, fragile skin, severe leg swelling and known allergy to the material among the reasons not to offer them. For people admitted with an acute stroke, NICE says not to use stockings but to consider intermittent pneumatic compression.

For acutely ill medical patients whose clot risk outweighs bleeding risk, NICE recommends medicine for a minimum of 7 days, with low-molecular-weight heparin as first choice. The guideline also acknowledges that heparins are of animal origin, which some people find a concern for religious or personal reasons, and says alternatives should be discussed.

NICE says people at increased risk should be given verbal and written information before preventive treatment is offered, covering their own risks, why prevention is important and its possible side effects, how stockings or compression devices should be used and how they can reduce their own risk by keeping hydrated and moving.

When you are discharged you should be told the signs of DVT and pulmonary embolism and to seek help if either is suspected. If you go home with injections or stockings, the guideline expects you to be able to use them correctly or to have help, to understand the importance of continuing for the recommended period and to know whom to contact if there is a problem. Your GP should be informed that you have gone home with preventive treatment.

NICE also advises that people consider stopping oestrogen-containing oral contraceptives or hormone replacement therapy 4 weeks before elective surgery, with advice on alternative contraception if they stop. That is a decision to make with your surgical team or GP rather than alone.

The NHS says there are things you can do to lower your chance of DVT: stay a healthy weight, stay active with regular walks, drink plenty of fluids and avoid sitting still for long periods, getting up and moving around every hour or so. It also advises not smoking and not drinking lots of alcohol.

For journeys of 4 hours or more by plane, train or car, the NHS suggests wearing loose clothing, drinking plenty of water, avoiding alcohol and walking around when possible. In its pulmonary embolism advice it adds choosing an aisle seat where possible, taking regular breaks from sitting, bending and straightening the legs, feet and toes every 30 minutes while seated, pressing the balls of the feet against the floor, and wearing flight socks. It advises against sleeping pills and too much caffeine.

The NHS says that if you think you have a DVT you should ask for an urgent GP appointment or get help from NHS 111. If you are pregnant you can also call an early pregnancy unit if you are under 20 weeks, or your maternity unit. A suspected DVT should be referred to hospital within 24 hours for an ultrasound scan.

Call 999 or go to A&E if you have DVT symptoms such as pain and swelling and also feel short of breath or have chest pain. For a pulmonary embolism the NHS lists severe difficulty breathing, pain in the chest or upper back, a very fast heartbeat and someone passing out as emergency signs. It says not to drive to A&E but to ask someone to drive you or call 999, and to bring your medicines.

If a clot is confirmed, treatment is with blood-thinning medicine. For a DVT the NHS says this usually continues for at least 3 months. For a pulmonary embolism it says injections of anticoagulant continue for at least 5 days and tablets for at least 3 months, and that you should make a full recovery if it is spotted and treated early.

In NHS hospitals the assessment and preventive measures described above are part of routine care for people admitted for medical illness, surgery or trauma, and they are provided free at the point of use. If you are having planned surgery privately, the same national guidance applies, and it is reasonable to ask the surgical team how your clot risk will be assessed and what prevention you will go home with.