This site is intended for health professionals only

VTE: risk factors, prophylaxis, diagnosis and treatment

Although often associated with hospital admission, venous thromboembolism (VTE) is a condition that spans both primary and secondary care, and therefore the diagnosis, management and prevention of VTE are relevant to healthcare professionals in both care settings. Kim Carter explains …

Kim Carter
RNDip HE BSc
DVT Nurse Specialist Portsmouth Hospitals NHS Trust

A deep vein thrombosis (DVT) is a clot that forms in the deep veins, usually in the leg or pelvis, although it can occur elsewhere in the body. A pulmonary embolism (PE) occurs when part of a blood clot breaks off and travels around the circulatory system, through the right side of the heart and into the pulmonary arteries. PE results in 30% mortality if untreated. Venous thromboembolism (VTE) is a term used to describe both DVT and PE.

Incidence
Although media interest in DVT is mostly associated with airline travel, with a few references to e-thrombosis (sitting at a computer for long periods of time), by far the biggest cause of VTE is hospital admission (either for surgery or with an acute medical illness). VTE also remains the biggest cause of maternal death in the UK, with the risk of DVT greatly increased during pregnancy and in the six weeks after delivery. With hospital inpatient stays becoming shorter, and more and more acute conditions being managed in primary care, knowledge of VTE and its management is essential for primary care practitioners.
VTE accounts for approximately 60,000 deaths per year in the UK, and more than 25,000 of these relate to hospital-acquired VTE.1,2 This equates to more than the total number of deaths from breast cancer, HIV/AIDS and road traffic accidents combined, and five times the number of deaths from MRSA.(1,2) These deaths occur in both medical and surgical patients and are largely preventable with risk assessment for all patients on admission to hospital, and the provision of appropriate thromboprophylaxis.
The total cost (direct and indirect) to the UK of managing VTE is estimated at £640m. Patients who have a nonfatal episode of VTE may develop lifelong morbidity in the form of post-thrombotic syndrome or pulmonary hypertension. One in three people who develop a DVT will develop some post-thrombotic symptoms within three years. Twenty-five percent of patients with a DVT will develop venous leg ulceration later in life, and the annual cost of managing leg ulcers in the UK is estimated to be £400m.(1)
The UK has been slow to introduce national guidelines on the prevention of VTE in hospitalised patients. Until April 2007, there were no such guidelines in England and Wales with the notable exception of the Royal College of Obstetricians and Gynaecologists (RCOG), who produce guidelines on the prevention of VTE in their patient population.
The American College of Chest Physicians (ACCP) arguably produce the most comprehensive guidelines on the prevention of VTE, which are largely accepted as the "gold standard".(3) The seventh edition of the ACCP Guidelines is currently available with the eighth edition due to be published 2008. The Scottish Inter-collegiate Guidelines Network introduced guidelines on the prevention of VTE in hospitalised patients in Scotland in 2002.(4) England and Wales, however, have been very slow to respond. It could be argued that this slow response is partly due to the lack of public knowledge of DVT, lack of media interest in the subject, and the resultant lack of government emphasis on its importance as a public health issue.
A recently published national audit by the All Party Parliamentary Thrombosis Group (APPTG) revealed that, although there are now national guidelines for VTE prevention in place in England and Wales, these guidelines are not being implemented correctly and unnecessary deaths are still occurring.5 The audit revealed that nearly 11,000 hospital patients might have died between the months of April and November 2007 as a result of NHS trusts failing to implement key recommendations on VTE prevention published in April 2007.5,6 The APPTG sent out a 16-question survey to medical directors of all the acute NHS trusts in England to ascertain the level of knowledge of hospital-acquired VTE, the steps that individual trusts are taking to combat the problem, and the level of concordance with recently published NICE guidelines and the recommendations of the expert working group on the prevention of VTE in hospitalised patients.(5) (For a summary of the results of this survey, see Box 1).

[[nip41_box1_38]]

Risk factors
If you asked a member of the public about DVT they would almost invariably cite airline travel as the most likely risk factor, with a small number highlighting the risk of e-thrombosis. Very few would cite hospital admission as a major risk factor for developing DVT despite the fact that 17% of all hospital inpatients are at risk of developing a DVT; and this risk increases considerably if a patient is over 40, having surgery or has a predisposing condition such as cancer or a thrombophilia.(1,2) As many VTE events occur after discharge from hospital, this is of particular relevance to primary care practitioners (see Box 2).

[[nip41_box2_38]]

It could be argued that the lack of media interest in hospital-acquired VTE and the resultant lack of public knowledge of this problem have lead to unrealistic perceptions of the health risks associated with hospital admission. The majority of patients entering hospital have an acute awareness and fear of developing a so-called hospital superbug, but never give a thought to the possibility of developing a DVT or PE, despite the fact that for the majority of patients, the latter poses a far greater threat.
The launch of the NICE guideline on reducing the risk of VTE in hospital inpatients undergoing surgery in April 2007 roused only a fleeting interest from the media and was not afforded much coverage in the popular press. The launch of the report of the Independent Expert Working Group on the prevention of VTE in hospitalised patients, also in April 2007, was met with similar apathy. There was a slight increase in media interest after the publication of the APPTG audit in November 2007, largely due to the continued campaigning of Lifeblood, the thrombosis charity.

Signs and symptoms of VTE
One of the major problems of VTE is that it can be a silent disease with sudden death being the first and only sign. It is essential that healthcare professionals in both primary and secondary care are aware of the risk of VTE in their patients and know when it is appropriate to provide thromboprophylaxis.
Symptomatic DVT often presents with one or all of the following symptoms in the affected limb: pain; swelling; pitting oedema; skin discoloration; warmth and engorgement of the collateral veins.7 However, as most of these symptoms can also be present in a number of other conditions (eg, cellulitis, ruptured Baker's cyst and lower limb surgery, trauma) misdiagnosis is common.
PE can present with sudden onset shortness of breath, pleuritic chest or back pain (often worse on deep inspiration) and sometimes haemoptysis.(7) Again, some of these symptoms can be present in other conditions such as costochondritis, pleurisy and pneumonia, so the correct diagnosis can be missed. It is important that patients who are at risk of VTE, whether because of constant or transient risk factors, are aware of the symptoms of DVT and PE so that they can seek timely and appropriate medical attention when necessary. Nurses play an important role in raising patient awareness.

Diagnosis of VTE
D Dimer
A blood test may be taken for a D Dimer assay. A positive D Dimer indicates the presence of an abnormally high level of fibrin degradation products in the body. Unfortunately this test is very nonspecific and an elevated D Dimer can be due to pregnancy, recent surgery, recent trauma, malignancy, infection and any chronic inflammatory condition as well as DVT and PE. A D Dimer should only be carried out when there is no clinical evidence of VTE and no risk factors. In this situation, a negative D Dimer can be useful in ruling out VTE and a positive result will highlight the need for further diagnostic investigations.

Doppler ultrasound scan
This is a noninvasive test that can evaluate blood flow and pressure by bouncing high-frequency sound waves off red blood cells. With modern techniques, it can detect DVT with reasonable accuracy. There is, however, some debate as to its accuracy in detecting small calf vein clots - experience of the sonographer, quality of the machinery and gross oedema in the affected limb can all affect diagnosis using this method.

Venogram
A venogram is a test whereby radio-opaque dye is injected into a vein in the foot or hand and then travels up through the veins of the limb. The dye is clearly visualised using X-ray imaging. If there is a DVT present in the vein, the dye will not flow freely through the vein and this will be seen as a gap in the pattern of dye. Although still seen as the "gold standard" in DVT diagnosis, increasing accuracy of less invasive diagnostic techniques, such as Doppler ultrasound, means that venography is being used less frequently as a firstline test. If, however, a Doppler test produces an equivocal result, venography is often used to confirm a diagnosis.

Ventilation/perfusion scan (VQ scan)
These tests use inhaled and injected radioactive material (radioisotopes) to measure breathing (ventilation) and circulation (perfusion) in all areas of the lungs. This involves two tests that can be used separately or together. During the perfusion scan, radioactive albumin is injected into a vein in the arm. The patient's lungs are then scanned as blood flows through them to detect the location of radioactive particles. The ventilation scan is the process by which the lungs are scanned while a person inhales radioactive gas. If a PE is present, this will show up as a missing area on the perfusion scan. This method of scanning is very accurate in a patient with normal lung pathology and a normal chest X-ray. In patients with chronic lung disease or an abnormal chest X-ray, however, a CT pulmonary angiogram is used.

CT pulmonary angiogram (CTPA)
For this test, dye is injected into the veins of the arm and then the chest is imaged using computed tomography (CT). If a PE is present it will show up as an area where there is no dye. This test is considered more accurate than a VQ scan, particularly where there is chronic lung disease or an abnormal chest X-ray.

Treatment of VTE
VTE is treated with anticoagulant drugs. These aim to thin the blood, prevent blood clots from growing any larger, prevent more clots from forming, prevent an embolism and give the body a chance to break down the clot or clots that are already present. There are currently two main forms of anticoagulants: heparin and warfarin.

Heparin
Heparin is usually given first and often when a diagnosis of VTE is suspected but not yet diagnosed. Heparin has an immediate effect and can be given by intravenous or subcutaneous injection.

  • Unfractionated heparin (UFH) can be given either by intravenous or subcutaneous injection. It needs careful monitoring to produce the required effect, but it has an advantage in that its effects can be reversed by protamine sulphate.
  • Low molecular weight heparin (LMWH) has a longer duration of action than UFH and can be given as a once-daily injection, and does not usually require monitoring. It also has an advantage in that it is associated with a lower risk of side-effects such as heparin-induced thrombocytopenia (HIT). However, its effects cannot be fully reversed and therefore where there is a high risk of bleeding, UFH may be the drug of choice.

As heparins are renally excreted, UFH is often the drug of choice for patients with renal impairment because of its ability to be closely monitored. This is particularly relevant in patients with a glomerular filtration rate (GFR) of less than 30 ml/minute. If LMWH is used in renal impairment, a reduced dose is given.

Warfarin
Warfarin is an oral anticoagulant that works by antagonising the effect of vitamin K. It takes at least 72 hours for the full anticoagulant effects of warfarin to be established. It is therefore given in conjunction with heparin for the first few days. Warfarin requires careful monitoring and its action can be affected by other medication, diet, liver function, alcohol intake and underlying illness. Warfarin is usually given for a period of three to six months for a first episode of VTE. In the case of recurrent VTE, however, lifelong treatment may be necessary.
There are some cases where warfarin therapy is inappropriate and a longer course of LMWH may be indicated. These include metastatic cancers, concurrent chemotherapy, pregnancy and liver disease. Long-term use of LMWH instead of warfarin is sometimes also chosen in IV drug users, especially when IV access is poor and a lack of concordance with monitoring is anticipated. Although UFH is usually used in an inpatient setting, LMWH and warfarin are often prescribed, administered and monitored in primary care.

Graduated compression hosiery
Graduated compression hosiery (GCH) can reduce the risk of post-thrombotic syndrome (PTS) following a DVT. PTS is associated with chronic pain, swelling, skin discoloration and sometimes ulceration of the effected limb. It is recommended that class 2 stockings be worn for a period of two years after a DVT; it is often primary care nurses who will be responsible for prescribing GCH and ensuring that stockings are fitted correctly.
 
Prevention of VTE: implications for primary care
Prevention of VTE is largely centred on careful risk assessment and the provision of appropriate thromboprophylaxis when indicated. Different types of prophylaxis and their indications are outlined in Box 3. In terms of acute medical illness and surgery, the secondary care setting is more traditionally associated with VTE risk than primary care. However, with shorter inpatient stays and with more acute illnesses being managed in the community, VTE risk assessment and the provision of thromboprophylaxis is relevant to both settings.

[[nip41_box1_42]]
 
It was noted by both NICE and the Department of Health that patients often develop their DVT and PE after discharge from hospital.(1,2,7) It is therefore essential that healthcare professionals in primary care are aware of the risk factors and are able to recognise the signs and symptoms of VTE, so that prompt diagnosis and management of VTE can be established.
The use of extended thromboprophylaxis is becoming increasingly common. Patients with cancer and patients who have undergone major orthopaedic surgery for example, may require daily injections of LMWH several weeks following discharge from hospital. Although the majority of patients are able to self-administer their LMWH, there will always be a small number who are unable to do so. This will undoubtedly have resource implications for primary care.

Conclusion
VTE is a common and potentially life-threatening condition that has implications to both primary and secondary care settings. Knowledge of the risk factors associated with VTE and available prophylactic methods is essential to healthcare professionals in all care settings. Awareness of the signs, symptoms, diagnosis and management of VTE is also vital.

References

  1. Department of Health. House of Commons Health Committee Report. The prevention of thromboembolism in hospitalised patients. London: DH; 2005.
  2. Department of Health. Report of the Independent Working Group on the prevention of venous thromboembolism in hospitalised patients. London: DH; 2007.
  3. Geerts WH, Pineo GF, Heit JA, et al. Prevention of venous thromboembolism: the seventh ACCP conference on antithrombotic and thrombolytic therapy. Chest 2004;126:338S-400.
  4. Scottish Intercollegiate Guidelines Network. Prophylaxis of venous thomboembolism. Edinburgh: SIGN; 2002. 
  5. Department of Health. All-Party Parliamentary Thrombosis Group. Thrombosis. Awareness, assessment, management and prevention, an audit of acute trusts. London: DH; 2007.
  6. Van Stralen KJ, Rosendaal FR, Doggen CJM. Minor injuries as a risk factor for venous thrombosis. Arch Intern Med 2008;168:21-6.
  7. NICE. Venous thromboembolism. reducing the risk of venous thromboembolism (deep vein thrombosis and pulmonary embolism) in patients undergoing surgery. Clinical Guideline 46. London: NICE; 2007. Available from: http://www.nice.org.uk/CG046

Resources
Lifeblood: The Thrombosis Charity
W: www.thrombosis-charity.org.uk
NHS Direct online
W: www.nhsdirect.nhs.uk
Anticoagulation Europe
W: www.anticoagulationeurope.org
Royal College of Obstetrics and Gynaecology
W: www.rcog.org.uk
Department of Health
W: www.dh.gov.uk/vte
National Institute for Health and Clinical Excellence
W: www.nice.org.uk/guidance