Deep Venous Thrombosis Ultrasound Evaluation

Anatomy and Physiology

Lower Extremity Venous Anatomy

The common femoral vein (CFV) starts at the inguinal ligament and bifurcates twice. The greater saphenous vein and the deep femoral vein (DFV) branch off medially and laterally, respectively. After these branch off the CFV, the CFV becomes the superficial femoral vein (SFV), which is the main deep vein of the lower leg. After passing through the adductor canal, the SFV becomes the popliteal vein, which subsequently trifurcates into the anterior tibial, posterior tibial, and peroneal veins. It is important to note the use of the correct anatomic nomenclature of lower extremity vasculature can be misleading clinically. The CFV and SFV make up the deep venous system in the upper lower extremity as they are the larger more central vessels in the leg. The DFV is a smaller superficial structure and therefore is not part of the deep venous system. It is because of this confusing nomenclature that many identify the CFV and SFV as just the femoral vein. When reporting identification or pathology of the DFV, such as a thrombosis of the DFV, this misleading nomenclature is usually also reported to prevent misdiagnosis of deep vein pathology.

Upper Extremity Venous Anatomy

The jugular vein and subclavian vein both branch off of the brachiocephalic vein. The subclavian vein bifurcates into the axillary vein and the cephalic vein, which is a large but superficial vein in the arm and forearm. The axillary vein gives off two branches of the brachial veins, which course alongside the brachial artery, before becoming the basilic vein, another large but superficial vein that continues for the length of the arm and forearm. When the brachial veins reach the antecubital fossa, it branches into multiple veins that each accompany an artery through the anterior compartment of the forearm.

Equipment

A high-frequency linear probe is an ideal probe to use for a DVT examination.It is ususally a vascular linear 7.5 MHz transducer to improve resolution. In patients with a body habitus that goes beyond the depth of the high-frequency probe, a curvilinear probe would be an alternative. If there is a preset mode for DVT scanning on the ultrasound machine, this should be used. If this is not available, "venous" is typically the best preset to select. "Vascular" and "small parts" are other options.

Personnel

Ultrasound to identify DVT of the lower extremity can be performed either by an experienced emergency medicine physician, an ultrasound technician, or another physician with appropriate training for ultrasound utilization. Identification of DVT in the upper extremity has not been as thoroughly studied to determine the ability of other individuals besides ultrasound technicians to perform the examination.[7][8]

Preparation

Lower Extremity

The patient should be in a gown with pants and undergarments removed. The patient should be draped to prevent unnecessary exposure. The patient should externally rotate the hip and have slight flexion of the knee to optimize positioning. The bed can be placed in reverse Trendelenburg position to increase the distension of the lower extremity veins, making them easier to identify. 

Upper Extremity

Initial positioning of the patient is lying supine with the head turned to the opposite direction of the arm being assessed and with the bed in Trendelenburg position. The arm should be extended and protonated, with the arm extending to approximately 90 degrees from the body. The forearm views can be best obtained with the patient sitting upright and the arm in normal anatomic position.

Technique or Treatment

Lower Extremity DVT Assessment: Classic Method

After the patient is positioned appropriately, a gel should be applied to the groin. The probe should be laid transversely at the inguinal ligament, identifying the common femoral artery and common femoral vein. The vein should be compressible at this site to assist in identification. Color mode and Doppler mode can also be used to differentiate between arterial and venous flow. Follow the vein distally, compressing every one centimeter. The greater saphenous vein will then come off of the common femoral vein, followed by the deep femoral vein. Follow the now superficial femoral vein by compressing every centimeter and then sliding down the leg. This repetitive sequence will occur until the SFV dives through the musculature in the mid to distal thigh, at which time it may no longer be compressible. 

The popliteal vein will be assessed by placing the transducer transversely on the posterior knee. The popliteal vein can be identified in the proximal popliteal fossa with the knee flexed at 10 to 30 degrees. The patient may need to lay on their side or lay prone to assess the popliteal vein better. Another option is to have the patient sit on the side of the bed with the knee hanging off the bed far enough to place the transducer behind it. This allows for the maximal venous distension due to gravity. Once the popliteal vein is identified, it should be followed proximally until it is lateral to the artery instead of anatomically posterior to it. Once this point is identified, serial compressions every 1 cm should be performed, moving distally. The end point is after the trifurcation of the popliteal vein when the popliteal vein becomes smaller and more difficult to visualize, which may occur in the calf rather than the popliteal fossa.

When completed, the following views should be obtained.

• High CFV: pre/post compression images or compression video proximally and distally
• CFV at saphenous intake, Sapheno-femoral junction with compression
• CFV at common femoral artery (CFA) bifurcation with compression
• CFA below CFA bifurcation with compression
• SFV at deep femoral vein intake: longitudinal and transverse views - pre/post compression images or compression video proximally and distally
• SFV below deep femoral intake: longitudinal and transverse views - color and Doppler flow proximally and distally
• Popliteal vein: longitudinal and transverse views - pre/post compression images or compression video proximally and distally
• Popliteal vein: longitudinal and transverse views - color and Doppler flow proximally and distally
• Posterior tibial and peroneal veins: color Doppler

The vein failing to collapse at any point is strongly suggestive of thrombosis.

Lower Extremity DVT Assessment: Two Point Technique

Using the same technique as above to identify the common femoral vein and the popliteal vein, assess only these two sights. The common femoral vein needs to be assessed from the ischial ligament until it becomes the superficial femoral vein. The popliteal vein needs to be assessed in the same manner as above, starting from where it is parallel to the popliteal artery and following it until the trifurcation. 

There has been further research on this method, indicating that the sensitivity would be increased by following the superficial femoral vein to the popliteal vein, making this similar to the classic technique, but limiting the assessment of superficial and calf veins.

Upper Extremity DVT Assessment

The starting point is the origination of the subclavian vein. The probe should be laid horizontally above the clavicle and at the base of the neck to assess this view, which will show the jugular vein and subclavian vein. Color flow through the subclavian vein needs to be identified. The vein should be scanned in both transverse and longitudinal views to ensure complete visualization.

The next view comes from the axilla, where the distal subclavian vein and complete axillary vein can be assessed. The probe should lie transverse to the vasculature from this point onward. These should be viewed in B mode and compressed to ensure complete collapsibility of the axillary and proximal brachial veins. Color flow should also be viewed of the distal subclavian vein and axillary vein.

The brachial veins should be followed by the length of the arm, compressing the brachial and basilic veins until the brachial veins bifurcate into the radial and ulnar veins.

With the patient sitting at the side of the bed, the length of the radial and ulnar veins should be scanned and compressed until the wrist is reached.

When completed, the upper extremity DVT series requires the following images to be considered complete.

• Subclavian Vein color flow: proximal and distal portions
• Axillary Vein color flow and pre/post compression images or compression video from subclavian vein to brachial vein
• Brachial vein: pre/post compression images or compression video proximally and distally
• Basilic vein: pre/post compression images or compression video proximally and distally
• Radial veins: pre/post compression images or compression video proximally and distally
• Ulnar veinsL pre/post compression images or compression video proximally and distally

The vein failing to collapse at any point is strongly suggestive of thrombosis.

Clinical Significance

Identification of DVT is important as proper treatment with anticoagulation can reduce progression to PE and SVCS, both diagnoses that carry serious morbidity and mortality. Identification of where the thrombosis is located, such as proximally (above the knee), distally (below the knee), or in or out of the deep venous system, is used to risk stratify patients to proper treatment and appropriate follow-up.

The ability to perform point of care ultrasonography to assess for lower extremity DVT, which accounts for 90% to 95% of total DVT, can significantly impact emergency room throughput and avoid unnecessary testing.[9] When the patient is considered low risk, bedside assessment can prevent the utilization of a d-dimer test and formal, elective ultrasonography. D-dimer has a high amount of false positive results, causing additional workup to be completed.[10] Elective ultrasonography is not always available, and the test usually takes one hour to perform. Bedside ultrasonography can decrease emergency room length of stay by approximately two hours, enhancing both emergency department throughput and patient experience.

Enhancing Healthcare Team Outcomes

Ultrasound to identify DVT of the lower extremity can be performed either by an experienced emergency medicine physician, an ultrasound nurse/technician, or another physician with appropriate training for ultrasound utilization. Identification of DVT in the upper extremity has not been as thoroughly studied to determine the ability of other individuals besides ultrasound technicians to perform the examination.[7][8] Whoever performs the ultrasound to rule out DVT must know how to interpret the images. Missing a diagnosis of DVT can be associated with disastrous outcomes and possible litigation. If in doubt, always consult with a radiologist.

Nursing, Allied Health, and Interprofessional Team Interventions

The nurse or nurse assistant can play an integral role in getting the patient prepared for the examination. The patient ideally needs to be in a hospital gown for either the upper extremity ultrasound evaluation or a lower extremity ultrasound evaluaion.  The nurse or nurse assistant can also assist with patient positioning during the exam, especially for the popliteal fossa evaluation.

Special considerations may need to be made for patients who are unable to lay flat due. The bed may need to be adjusted to allow the patient to be supine while still keeping the head elevated. If the patient cannot lay supine, additional support will definitely be needed for positioning during the examination.

A nurse or nurses assistant can also help workflow by having equipment ready at the bedside. The ultrasound machine needs to have the high frequency linear probe turned on and plenty of gel needs to be available. There should also be towels for wiping the patient off when the exam is complete and the appropriate wipes to clean the equipment.

Nursing, Allied Health, and Interprofessional Team Monitoring

No specific monitoring is needed during the examination unless another medical comorbidity makes it necessary.