Deep Vein Thrombosis (DVT) Duplex Ultrasound

Deep vein thrombosis or DVT can occur in any of the deep veins of the body. DVT is common in hospital patients who require confinement in bed for long periods after surgery and trauma and in patients with malignancy and blood clotting disorders. Patients who have had knee and hip surgery, who have had catheters in their axillary, subclavian, jugular and central veins  and people who have been on long distance plane flights are also more likely to suffer DVT.

Complications of DVT can be a pulmonary embolism, so medical advice and treatment is required for all cases of DVT. DVT in the leg veins can damage the valves within the veins which can lead to chronic reflux in these veins. This can cause changes in the skin of the lower calf and increase the incidence of ulceration. This deep venous reflux can also lead to chronic leg swelling and secondary varicose veins. The symptoms of DVT can be swelling, inflammation and localised pain and tenderness.

Duplex ultrasound can be used to assess the patency of the deep veins of the neck, abdomen and upper and lower extremities. These veins can be assessed for the presence of thrombus, with the site and extent of the thrombus documented for repeat scanning. The function of these veins can be also assessed.

PATIENT PREPARATION AND EXAMINATION TECHNIQUE:

For examination of the abdominal veins he patient will need to fast for 6 hours if possible in order to minimise bowel gas and optimise image quality.

For examination of the upper or lower limbs the patient will need to have the limb in question exposed in its entirety. The patient should wear loose fitting clothes or be prepared to remove the outer garments of the extremity. The investigation is performed in complete privacy.

The patient is examined lying in a dim, quiet room. The area of interest should be exposed and gel applied to the skin. The probe will be moved over the area interest with B-mode and Doppler ultrasound used to visualise the veins in question and determine patency. B-mode ultrasound is used to visualise the walls of the vein. Compression of the vein with the probe will demonstrate patency. The vein will not compress completely if there is thrombus within the vein. Colour Doppler ultrasound can be used to demonstrate patency and function of the vein and can also help to diagnose non-occlusive and partially recanalised thrombus.

A detailed history from the patient should be taken with particular attention paid to the area of most pain or tenderness. The examination of the leg veins for DVT may need to be extended to the iliac veins and IVC if indicated. Examination of the superficial veins of the extremities may also be required.

EXAMINATION TIME:

The examination time is dependent on the site of the examination and how many areas need to be examined. The examination may take up to 60 minutes.

DIAGNOSTIC CRITERIA:

The presence of thrombus within the deep veins is determined by whether the vein is fully compressible. If the vein is not able to be compressed due to anatomical difficulties or patient pain then the vein must be adequately seen with B-mode ultrasound and must demonstrate full venous filling with leg or arm augmentation or respiration.

Failure to adequately seen the margins of the vein and demonstrate full venous filling requires reporting of an inconclusive test.

The presence of occlusive, partially occlusive or recanalised thrombus within the deep veins should be recorded with the position and extent of the thrombus measured against anatomical landmarks. An attempt should be made to determine if the thrombus is acute or chronic.

A detailed worksheet should be generated documenting the sites and extent of DVT to assist the sonographer when performing repeat examinations to determine the progression of the DVT. A formal report should be generated and the referring doctor notified immediately of any positive results.