| Equipment | - High-frequency linear transducer (superficial)
- Curvilinear transducer (deeper structure or if obese)
- Colour flow (Video S2) or spectral Doppler may be required to confirm whether a vessel is an artery or a vein
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| Patient positioning | - Reversed Trendelenburg position with the bed tilted up to 20° to allow venous dilatation from blood pooling
- Knee 20–30° bend and hip 30° externally rotated (frog’s leg position) to allow full access to the medial part of the thigh and the popliteal fossa
- The popliteal vein can also be evaluated with the patient in decubitus position with the study leg side up
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| Examination technique | - Discrimination of arteries and veins is critically important, and the following features are useful:
- oVeins are easier to compress with external force from the probe than arteries, which is the most reliable technique. Only veins contain valves
- oArteries have a more visible (thicker) wall, are pulsatile and may have atherosclerosis
- The relationship of the artery to the vein is not a reliable method of discrimination between the two types of vessel
- If any doubt, colour or pulsed-wave Doppler can be used
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| Examination technique | - Transverse 2-D ultrasound imaging with compression
- Probe’s indicator to the patient’s right
- Three-point technique examines the junction of the common femoral and greater saphenous veins, the femoral vein and the popliteal vein and GSV
- Two-point technique examines the junction of the common femoral and greater saphenous veins and the popliteal vein
- The common femoral vein represents the most medial vessel inferior to the inguinal ligament, which connects the pubic symphysis to the anterior superior iliac spine. The common femoral vein usually extends 2 cm proximal and 2 cm distal to junction point between the common femoral and greater spahenous veins
- Point 1 is defined at the junction of the common femoral and greater saphenous veins, which has a clinical significance where DVT at the junction point should be treated. In this view, the femoral and profunda femoral arteries are usually visualised
- Point 2 is defined at the femoral vein, which is essentially located in the adductor canal below the junction of profunda femoral and femoral veins
- Point 3 is defined at the popliteal vein and is located in the popliteal fossa
- With the indicator pointed to the patient’s right, the PV is located in the near field of the image and is anatomically more posterior when compared to popliteal artery
- Examiner will image the veins at the three described points, then will apply compression in an attempt to completely compress the vein.
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| Assessment of deep venous thrombosis | - In the absence of DVT, the walls of the vein should coapt, completely obliterating the vein’s lumen, and the adjacent artery may become deformed with compression
- Non-compressible vein indicates the presence of DVT
- Note the degree of occlusion: irregular, heterogenous
- Form, length and mobility
- Acute thrombus: anechoic to hypoechoic, poorly attached, spongy texture, dilated vein
- Chronic thrombus: hyperechoic or brightly echogenic, well attached, rigid texture, calcifications, contracted vein, large collaterals, thickened vein walls
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| Associated features | - Raised D-dimers
- Wells score
- Lung: subpleural infarcts
- Heart (in larger PE’s): right ventricular dilatation and dysfunction and D-shaped septum,50 dilated inferior vena cava, McConnell sign, mobile thrombus (rarely seen)
- Unilateral limb desaturation with near-infrared spectroscopy
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