Quality Assurance At Least 3 pairs of transverse images (with and w/o compression) with Name, MR #, and views labeled: CFV (Common Femoral Vein) Superficial Femoral Vein (Must get to trifurcation) Popliteal Vein Sagittal images and real time sweep through entire lengths of vessels should be done, but do not need to be printed.
General
This will probably replace renal as the sixth essential scan High resolution linear array Place patient in 30-45° of reverse Trendelenberg or let leg dangle off of the table to distend the veins or have head elevated Start as proximal as possible to find the common femoral vein and artery. Confirm placement with color power Doppler, artery will obviously have pulsatile flow, while veins flow constantly with respirophasic variation (breathe in or valsalva and flow is less). Can augment flow by squeezing calf. Can check flow reversal by squeezing proximal, should only see less than ½ second of reverse flow if valves are patent (chronic DVTs cause valvular insufficiency.) After color power Doppler, confirm with pulsed Doppler. Here venous and arterial are obviously different, with the arterial waveform much higher and narrower. Imaging CFV at inguinal crease Proximal portion of GSV and PFV Entire length of SFV Entire length of PV until distal trifurcation (Bend knee or dangle leg) That being said, all EMBU studies have used compression of solely common femoral and popliteal with excellent sensitivities. Must have complete compression of the vein in order to be negative. Sometimes you will have to put your hand opposite the probe to aid compression. Obviously much harder with a curved probe than a linear one. Popliteal vein is superficial to artery Acute DVTs Clot will initially be hypoechoic, progressing over hours to days to a echogenic clot. Noncompressible vein over and distal to clot. Absence of flow augmentation. May see vein distension. Chronic DVT Hyperechoic clot Non-compressible Normal to decreased flow, may allow augmentation Venous reflux will be greater than 1 sec e process of compression then relaxation follows by moving 1 cm distally and continues until the common femoral vein splits into the deep femoral and superficial femoral veins. After the saphenofemoral junction is compressed and the transducer is moved distally, the femoral artery will typically split into the deep femoral and superficial femoral arteries, if it did not already occur. The junction of the deep femoral and superficial femoral veins is almost always 1 or 2 cm distal to the split of the common femoral artery. An unnamed perforator frequently comes into the common femoral vein just proximal to the junction of the deep femoral and superficial femoral veins. Although anatomic relationships vary, the deep femoral vein typically disappears deep into the thigh shortly after it is first identified on a proximal to distal descent. The superficial femoral vein continues just under or occasionally next to the superficial femoral artery. The junction of the deep femoral and superficial femoral veins can be surprisingly confusing. In a proximal to distal descent, the deep femoral vein may appear to quickly switch locations with the deep femoral artery in cross section. This can lead to doubt as to which vessels are expected to remain open with transducer pressure (arteries) and which should collapse (patent veins). Pulse-wave Doppler can be exceedingly helpful in identifying each of the four vessels. This may be a moot point in a thin extremity with good veins, but it can salvage an examination in the typical obese or edematous leg, in which clinical suspicion is high. After collapse of the deep and superficial femoral veins for the first 1 or 2 cm is verified, the examination moves to the popliteal region. To examine the lower leg, the transducer is placed behind the knee, and the popliteal artery and vein are located in cross section (Fig. 3). There should be no smaller vessels around the two or the transducer is too distal (Fig. 4). Occasionally, the trifurcation of the popliteal vein occurs very proximal, high behind the knee. The examination should capture the last 2 cm of the popliteal vein and end just distal to the trifurcation. Just as in the upper leg, compression of the vein, or veins, is followed by sliding the transducer distally for 1 cm, where compression is repeated again. Although calf DVTs are relatively less important and frequently not treated, it may be helpful to be aware of them, especially when one is close to entering the popliteal vein. Scanning through the trifurcation by 1 or 2 cm allows the sonologist to ensure all three vessels that make up the popliteal collapse. If one of the branches is thrombosed proximally, it is likely to seed the popliteal shortly, turning into a proximal DVT. The calf DVT should be treated or watched very carefully with serial ultrasound examinations if anticoagulation is contraindicated in the particular patient. Go to source: Critical Care Medicine – Fulltext: Volume 35(5) May 2007 p S224-S234 Ultrasound in the detection of venous thromboembolism
Blaivis description of how to perform study:
The focused approach, originally proposed by radiologists, contends that deep vein thromboses do not form in isolated small plugs but grow from smaller to larger vessels and either propagate proximally or resolve.[7], [13], [14] and [15] Thus, proximal deep veins in the lower extremity are sampled at key points, rather than every centimeter. This has occasionally been misinterpreted as just 2 compressions with the probe over the course of the entire leg. In actuality, the goal is to sample the common femoral vein’s junction with the deep and superficial femoral veins by compressing a short segment of vasculature, typically 3 or 4 cm, with approximately 3 or 4 compressions. Ideally, the junction of the common femoral vein with the greater saphenous vein is also included to catch proximal greater saphenous thrombi that are about to seed the common femoral vein. These are treated like a deep venous thrombosis rather than superficial vein thrombi because of the high risk of propagation into the deep venous system. The next segment surveyed is behind the knee, compressing down the distal popliteal vein just through the initial trifurcation into the calf veins. Again,
3 or 4 compressions over 3 or 4 cm allows detection of popliteal vein deep venous thrombosis and distal or calf thrombi seeding the popliteal vein
False Positives
· Bakers Cysts, confirm with color Doppler · Lymph nodes, may have blood flow scan distal and proximal to show round structure, not a vessel
Ultimate Evidence
Thromb Haemost. 2012 Nov 8;109(1)