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Learning Objectives:
Describe the technique for performing vascular assessment for deep vein thrombosis (DVT)
Identify venous thrombosis by visualization of the endoluminal thrombus and performing a compression study
Knowledge of when not to perform compression maneuver if there is a visible thrombus.
Identification of relevant anatomy: common femoral, greater saphenous, superficial femoral, deep femoral and popliteal vein with differentiation from popliteal artery.
Identification of adjacent structures such as lymph node, mass and hematoma.
Key Points:
DVT assessment through POCUS is a rapid evaluation that permits the visualization of large clots in the femoral and popliteal veins.
DVT is diagnosed by lack of compressibility, visualization of the clot or by color Doppler.
Compression maneuvers on a visible clot can lead to its embolization.
Deep Vein Thrombosis Assessment
Deep Vein Thrombosis Assessment
Patients that require POCUS evaluation are unstable and transport for performing US evaluation is difficult and inconvenient. In these patients, rapid evaluation by POCUS is an efficient method for ruling out the presence of a DVT in the main vessels of the lower extremities.
The main indications for performing a DVT evaluation are:
Clinical concern for a DVT or PE,
Undifferentiated shock or
Hypoxemia and newly discovered right ventricular dysfunction (1).
POCUS assessment for DVT is a limited evaluation that is focused on the common femoral vein branch points and the popliteal veins. A complete evaluation would include the entire extent of the femoral vein.
If there is very high suspicion for a DVT, a complete evaluation should be performed since it has been reported that 8 to 22% of DVT are located outside of the limited examination sites (Kory 2011, Maki 2000).
The clots are most commonly visualized by three methods in the standard POCUS evaluation.
Direct visualization of the clot: a hyperechoic figure is seen within the vessel that can be either partially or totally occluding its lumen.
Lack of compressibility: a normal vein should be able to be completely compressed when doing pressure with the probe, lack of compressibility indicates presence of a clot even if it cannot be directly visualized.
Color Doppler: lack of blood flow visualized by color doppler indicates presence an obstruction within the vessel. This test is not routinely done and not performing it doesn't decrease the diagnostic yield of the previous methods (Blaivas, 2007; Kory 2011).
Technique for Performing DVT POCUS Evaluation
Place the patient in supine position, with the knee slightly bent and the leg externally rotated.
Utilize a high-frequency transducer (like the linear array aka the vascular probe). Marker pointing to the right of the patient (9 o'clock position). A minimum of three sites in the groin region and the popliteal fossa is recommended.
Identify the common femoral vein (CFV) and then perform compression from above the inguinal ligament at the proximal portion of the external iliac vein. Compress every 1-2 cm while moving distally along the CFV, until the common femoral vein is seen branching into the superficial and deep branches and the veins become deeper. Make sure you increase the depth of your probe as you advance your probe caudad.
Scan the popliteal vein by flexing the knee 45° while externally rotated. The popliteal vein (PV) overlies the popliteal artery (PA). Perform compression at this site. Avoid putting too much pressure in the fossa or lifting the knee of the patient with the probe as this may be alreading compressing the vein.
Considerations and Limitations of POCUS DVT Evaluation
The hyperechoic image of a clot within the vessel or "smoke" could be present in low-flow states and should not be confused with a clot, in the absence of other diagnostic findings.
Chronically organized thrombi adhere to the wall and become more hyperechoic and more resistant to compression. It is important to differentiate between a chronic and an acute DVT. Always consider asking for consultation of a more experienced sonographer when in doubt about a finding.
When performing a vascular assessment of the lower extremity it is possible to observe other findings in the ultrasound that might be confused with a DVT, most commonly hematomas, enlarged lymph nodes and cysts.
Lymph node (upper image): these produce a round hypoechoic image that is non compressible. They are commonly located close to the large vessels in the groin. They can look similar to a DVT in a single image, so it is important to continue scanning longitudinally to differentiate between a node and a vessel.
Hematoma (lower image): formation of hematomas within muscle fibers can appear to be round non-compressible images that can be confused with a DVT. In a similar way than with lymph nodes, tracking the image will differentiate it from a vessel. (image courtesy of ultrasound.info)
Cysts: produce a round anechoic image that is non-compressible. See below a Baker's Cyst that can be easily confused with a popliteal DVT (image courtesy of POCUS Atlas).
DVT of left common femoral vein in a patient with entire left lower extremity pain and swelling. Observe non-compressibility of vein when pressure is applied (vein is medial, which in this case is the one to the left of screen)
Artery can be seen as the pulsating thick walled vessel under color doppler. Vein is seen to the left with echogenic material and flow only around the edge of the clot. Inability to compress the vessel would confirm the diagnosis of DVT (not pictured).
Intensive Care US II Vascular US Kory Silverberg Annals ATS 2013.pdfReferences:
1.- Silverberg, MJ; Schmidt, GA. ATS Seminars, Central Venous Access and Venous Diagnostic Ultrasound. Ann Am Thorac Soc Vol 10, No 5, pp 549–556, Oct 2013
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