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National Clinical Guideline Centre – Acute and Chronic Conditions (UK). Venous Thromboembolism: Reducing the Risk of Venous Thromboembolism (Deep Vein Thrombosis and Pulmonary Embolism) in Patients Admitted to Hospital. London: Royal College of Physicians (UK); 2010. (NICE Clinical Guidelines, No. 92.)

Foreword

The second report of session 2004–5 of The House of Commons Health Committee ‘The Prevention of Venous Thromboembolism in Hospitalised Patients’ opens with these worrying statistics: Each year 25,000 people in the UK die from venous thromboembolism. This figure includes both patients admitted for medical care of serious illnesses, as well as, those admitted for surgery. The report goes on to state that this is a larger number of deaths than are attributable to breast cancer, AIDS and road traffic accidents combined. It is 25 times the number of people who die as a result of MRSA infection 286.

The sudden killer is pulmonary embolism (PE). That is a thrombus (or blood clot) which forms in the lower limb or pelvic veins and then comes loose and is carried in the blood to lodge in the lungs. Acute massive pulmonary embolism often kills immediately. If the patient survives the immediate haemodynamic consequences, death may still ensue in the days or weeks that follow. Survivors of the initial event may eventually recover after a protracted hospital course including some time in intensive care.

Deep vein thrombosis (DVT) is in itself a cause of substantial morbidity and may lead to the development of post thrombotic syndrome (PTS) with chronic swelling and ulceration of the legs amongst its manifestations. Add this burden of morbidity to the estimated 25,000 deaths and it becomes a massive health problem. This is the perception of the situation as presented to the Health Committee, the CMO by expert advisors and patient representatives.

Many of these deaths are in patients admitted for medical care but some have gone into hospital for a planned surgical operation such as joint replacement, gynaecological surgery or gall bladder removal intended to improve their quality of life, or for a cancer operation with the hope of cure. Characteristically it is several weeks after surgery, when recovery is in sight that this tragedy strikes. Our guideline covers all patients admitted to hospital and includes patients having surgery in day-case facilities. The magnitude of risk of venous thromboembolism (VTE) is dependent upon factors inherent in the operation and factors related to the individual patient. It is the combination of these factors which defines certain patients as at increased risk of VTE. A key part of this guidance is systematic risk assessment of all patients either on admission in the case of emergencies or prior to admission for planned surgery. This evaluation must be repeated regularly during a hospital stay because the balance of risks of bleeding and of VTE change as the condition of the patient changes. The part of our work relating to risk assessment has been done in close collaboration with the Department of Health and the Chief Medical Officer’s VTE Working Group as part of the national VTE prevention strategy.

Surgeons have been acutely aware of the dangers of VTE and have been central to research from the 1970s and 1980s642. Physical methods (such as graduated compression/anti-embolism stockings, foot impulse and intermittent pneumatic compression devices) and pharmacological treatments (such as heparin and warfarin) have been studied in a plethora of randomised trials. Both physical and pharmacological treatments have been shown to reduce the incidence of DVT under study conditions. The difficulty is knowing how to implement prophylaxis in practice. Will reduction of DVTs translate into reduced death rates from PE?

There is a question over whether the incidence of PE bears a reasonably consistent numerical relationship to the more frequent clinical event of DVT. We have not simply accepted this as an assumption but, where data sets allow both to be counted, we have tested the hypothesis. There appears to be a reasonably consistent association. However, this putative relationship between detectable lower limb DVT and fatal PE may break down in special cases such as knee replacement. The next question is whether reducing the incidence of DVT (the more numerous and more readily studied outcome) will result in a proportionate reduction in potentially fatal PE. Again we have tried to test this extrapolation against the data. We have conducted analyses where data are sufficient such as in studies of unfractionated heparin versus no prophylaxis: and found a similar reduction in fatal PEs473. A note of caution must remain however. We generally lack evidence for reduction in all-cause mortality which would require very large trials.

The pharmacological methods introduce another consideration. They carry with them a new risk - that of bleeding. It is major bleeding events which are counted in the RCTs. We have to give guidance concerning the method of VTE prophylaxis which steers the safest course between the competing risks posed by thrombosis on the one hand and bleeding on the other.

Major bleeding is clearly a threat to life but under some circumstances, a low volume bleed can be a very major complication. A few millilitres of bleeding into the brain, or compressing the spinal cord within the vertebral canal can cause death or permanent neurological damage. Small volumes of bleeding into a joint can cause the operation to fail and the patient will be worse off than before.

It is a clinical problem which requires a meticulously researched and analysed evidence base. The potential health gains for the optimal strategy are great. An individual team will have patients who suffer PE and patients whose recovery is complicated by a treatment related bleed. The clinical difficulty is that both fatal pulmonary embolism and major bleeding have low event rates affecting fewer than one in a hundred patients. We cannot emphasise too strongly that it is evidence from the best available randomised controlled trials that we must use to quantify these competing risks. Clinical impressions cannot adequately capture the trade off between risk and benefit, particularly where both relate to infrequent clinical events or where the manefestations are delayed. It has been well shown that if clinicians base decisions for future patients on a recent adverse event in their own experience, those decisions are not likely to be in the best interest of future patients 108.

The impossibility of basing a policy on clinical experience makes it essential to rely on evidence based guidance. It is appropriate that this guidance is made available for individual clinicians and their teams to use in framing locally implemented prophylactic policies. Hence VTE prophylaxis is an ideal subject for an evidence based guideline. The complex task has been undertaken in collaboration between the scientific staff at the NCC-AC, and the medical professionals of the Guideline Development Group (GDG).

There are important changes expected in anticoagulation if the oral agents recently licensed or currently undergoing evaluation prove to be safe and consistently effective. We have been cautious in our recommendations, but if during the lifetime of this guideline they fulfill the hope that many doctors have for them, they will simplify practice that at present relies on daily injections of an anticoagulant, although there will need to be consideration of their drug interactions.

A summary of our recommendations:

Mechanical methods have been proven to be effective in surgical patients and do not to add the risk of bleeding. We have recommended these methods for patients at risk of bleeding and in combination with pharmacological methods for many groups of patients. However during our work on this guidance a large study in stroke patients did not show any beneficial effect of stockings in stroke patients but did show an increase in skin complications associated with their use. This influenced our recommendations 158.

In patients at higher risk of VTE, the use of pharmacological methods is cost effective. In surgical patients these are often to be used in combination with mechanical prophylaxis such as stockings as this was the case in many of the RCTs on which we rely.

There will be patients who are already on antiplatelet medication; there will also be some for whom aspirin may be recommended in the perioperative period for the reduction of risk of heart attack and stroke. This may present a therapeutic conflict: clinicians will be concerned about the risk of bleeding. It should be noted that while aspirin does reduce the risk of VTE to some extent, we have not recommended it as a form of VTE prophylaxis. Aspirin has an important role in cardiovascular perioperative risk reduction, but this is outside our scope. It might be tempting to see antiplatelet therapy as a convenient prophylactic “two for one”. To use this as a clinical justification for omitting recommended VTE pharmacological prophylaxis risks is not recommended because the protective effective of aspirin against VTE is insufficient

Although there are many trials, we still found ourselves with uncertainties. For example, the true present day rate of DVT and PE is very hard to ascertain. Many more patients have less invasive surgery. Surgical patients get out of bed sooner. High emphasis is placed on early mobilisation and early discharge from hospital. Prophylaxis (both mechanical and pharmacological) is widely used, but practice varies and implementation is probably patchy. There is a strong sense that DVT and PE are less of a problem than they used to be in surgical patients but maybe it is hidden from the view of clinicians by early discharge rather than being truly reduced because 80% of DVT are subclinical and the average DVT occurs on the 7th postoperative day, long after the patient has left hospital.

High quality monitoring of adverse events will be needed to ensure that these recommendations are as safe as they can be and we emphasise strongly the need to implement the research recommendations. These research recommendations specifically target the area where we found the biggest potential consequence from uncertainty. We also welcome the recommendation of the House of Commons Health Committee: “Systems must be put in place to ensure that the NICE VTE guidelines are implemented” 286. Once implemented, we need to monitor adverse events, both bleeding and venous thromboembolism to ensure that guidance is steering the safest course between those competing risks to all patients admitted to hospital.

Professor Tom Treasure MD MS FRCS FRCP

Chair, Guideline Development Group

Copyright © 2010, National Clinical Guideline Centre - Acute and Chronic Conditions.

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Cover of Venous Thromboembolism
Venous Thromboembolism: Reducing the Risk of Venous Thromboembolism (Deep Vein Thrombosis and Pulmonary Embolism) in Patients Admitted to Hospital.
NICE Clinical Guidelines, No. 92.
National Clinical Guideline Centre – Acute and Chronic Conditions (UK).

NICE (National Institute for Health and Care Excellence)

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