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Deep Vein Thrombosis – DVT

Summary

Deep Vein Thrombosis is exactly as its name suggests: a clot in the veins. They can occur in any vein, although they are much more likely in the veins of the pelvis and legs. If they occur in other locations (e.g. in the arm) they are often indicative of a more sinister underlying cause (e.g. clotting disorder, carcinoma, or an increased clotting risk of unknown cause) and are more likely to require life-long treatment / prevention. On their own, they are not particularly significant, however, they are dangerous because they can embolise, and cause a pulmonary embolismthese can be fatal.

Some studies suggest a ‘silent’ PE in up to 40% of DVT patients.

Aetiology

Virchow’s triad of risk factors:

Signs & Symptoms

Diagnosis

This is often made clinically, using the Well’s score. Treatment can be initiated in cases of high clinical suspicion without further investigation, although in reality often an USS is used for confirmation. Also be aware that there are two separate Well’s scoring systems: one for DVT and one for PE.

Differentials

Pathology

A clot develops at a site of damage to a vessel wall (e.g. an atherosclerotic plaque, or perhaps a site of trauma). This can impair venous drainage of the leg. Clots below the knee will rarely embolise, but above the knee, they are far more dangerous. They will often spontaneously resolve over time, however, they are usually treated to reduce the risk of embolism.

Investigations

Treatment

The aim is to prevent embolism.

LMWH – this is usually started as soon as the diagnosis is made, and is normally continued for a minimum of 5 days. It is usually stopped when the INR is in the target range (2-3)
Warfarin – also started at the same time as heparin, but warfarin actually increases coagulability in the first few days of use; hence the use of heparin initially. Warfarin is continued for:

More Information

Introduction

  • 25-50% of all surgical patients will have a DVT.
  • 65% of all below the knee tumours will be asymptomatic. Below the knee tumours rarely embolise to the lung
  • More common in veins (than arteries) due to the slower flow of blood.
  • They can occur in any vein, but by far the most common places are the legs and pelvis. They can also occur in the arms, although these are less likely to cause direct problems, and are also far less likely to cause PE.

Risk Factors

  • Age
  • Obesity
  • Varicose veins
  • Immobility (generally bed rest >4 days)
  • Pregnancy (oestrogen)
  • Previous DVT / embolism
  • Antithrombin deficiency
  • Protein C deficiency
  • Oestrogen therapy (Pill, HRT) – note only the combined pill, not the progesterone only pillonly a small risk factor.
  • Trauma
  • Surgery – especially pelvic and orthopaedic
  • Recent MI (10% of MI patients will have a DVT)
  • Infection
  • Malignancy
  • Dehydration
  • Congestive heart failure
  • Inherited clotting deficiencies – thrombophilia – factor V Leiden

Virchow’s triad

This is a little way to remember three of the major causatory factors of thrombosis

 

Signs

Differentials

Well’s criteria for determining the clinical probability of a DVT
Clinical feature
Score
Active cancer – treated within the last 6 months, or undergoing palliative treatment
1
Paralysis, paresis, plaster immobilisation of leg
1
Major surgery or recently bedridden (>3 days in last 4 weeks)
1
Local tenderness along the distribution of the deep venous system
1
Entire leg swollen
1
Calf swelling >3cm compared to other leg (measure them both at exactly the same point, usually 10cm below the tibial tuberosity)
1
Pitting oedema (greater in symptomatic leg)
1
Collateral superficial veins (non-varicose)
1
Alternative diagnosis as likely or more likely than that of DVT
-2
It would be pretty hard to remember this on the day! So for on the job, you can use the following quick and easy method:

Investigations

Coagulation investigations

The normal INR value is between 0.9 and 1.3. When someone is on warfarin therapy, the target is usually between 2-4 but may vary for individuals.

D-dimer

This is a test for thrombosis
Other causes of a positive result include; infection, inflammation, pregnancy, malignancy, recent bleed, stroke, infarct, trauma, and post-op.
D-dimer is a fibrin degradation product. It will be raised for approximately 3 weeks after a clot.
Measure the leg!
Chose a point, e.g. 3cm below the tibial tuberosity, and measure the circumference on both legs. A difference of >1cm is significant, and >3cm is serious!

Venography

This is the gold standard test!
Radio-labelled dye is injected into a vein on the dorsum of the foot, and is then imaged by ‘dynamic x-ray imaging’. Static films are also taken to provide a permanent record.
Venography for DVT’s in the pelvis and IVC can be done by femoral vein catheterisation.

Venometer

Basically a BP cuff you put round the calf, pump it up to occlude circulation, then let it down, and in a normal patient, blood should flow straight away. You get a graph of blood flow. If the flow is reduced, then there is a likelihood of thrombus.

Doppler USS

Doppler ultrasounds demonstrating DVT. Note the red and blue overlay which indicate blood flow away from and towards the probe in a doppler scan. The lack of this colour overlay in the arrowed area is indicative of the presence of clot. This file is taken from wikimedia commons and is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.

Fibrinogen testing

Give radiolabeled fibrinogen injection, then look at areas where it collects.

ECG

S1-Q3-T3 – commonly comes up in exams, but not often seen in clinical practice.

Prevention

Treatment

The main aim is to prevent pulmonary embolism.
All patients with thrombus above the knee should receive anticoagulation. Patients with a DVT below the knee will usually receive 6 weeks of LMWH as 30% of the these patients actually have an extension of the clot proximally if nothing is done.
Bed rest is also advised until the patient is fully anti-coagulated.
LMWH’s (e.g. enoxaparin 1.5mg/Kg/24hr) are more effective than unfractioned heparin. Give 5 days worth minimum! Don’t give warfarin on its own!! Remember that it increases coagulation for the first couple of days after administration. Thus typical treatment would be a combination of LWMH and warfarin, started at the same time, and then the LMWH stopped when the INR reaches the target range (usually 2-3). Continue warfarin for:
Once the patient is mobilised (i.e. after the period of bed rest), they should wear elasticated stockings! These will reduce the risk of superficial thrombophlebitis as they prevent the pooling of blood in the superficial veins as these become full from their use as collaterals from the primary clot.
The stockings can reduce the incidence of secondary thrombophlebitis by 50%, however the evidence for this is not very solid.
IVC filter – in some rare cases where anti-coagulation fails, then an IVF filter may be implanted to reduce the risk of PE.
Thrombolysis is rarely used, there have been trials, but these have been inconclusive.
Recurrence
Depends on the risk factors – if it is post-op, then probably not very likely, if it is idiopathic, then 5 year risk is about 30%.

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