Venous thromboembolism is a major national health problem, with an overall age- and sex-adjusted incidence of more than 1 per 1,000 annually.¹ Because the incidence of this disease is so high and progression from deep vein thrombosis (DVT) to pulmonary embolism (PE) can lead to significant morbidity and mortality, the ability to rule in or rule out DVT in the emergency department is essential.

Ultrasound is a sensitive and specific tool for the assessment of patients presenting with symptoms suggestive of lower extremity DVT.² Focused ultrasound of the lower extremity can be performed quickly by emergency physicians using a simplified three-point compression technique that concentrates on the evaluation of those areas with highest turbulence and at greatest risk for developing thrombus: 1) the common femoral vein at the saphenous junction, 2) the proximal deep and superficial femoral veins, and 3) the popliteal vein.³

Previous research has suggested that the three-point compression technique allows emergency physicians to determine in as few as 4 minutes and with 98% correlation with the radiology-performed complete duplex ultrasound examination the presence or absence of lower extremity DVT.⁴

A more recent article found that in a heterogeneous group of emergency clinicians, including residents and mid-level emergency providers with different stages in training in ultrasound, the accuracy rate is closer to 85%.5 However, this study also noted that in cases when the clinical gestalt impression of the clinician was that the patient had a high pre-test probability for DVT, the combination with the three-point compression lower extremity ultrasound had a high positive likelihood ratio for DVT.

Clinical Indications

Emergency physicians should consider performing a three-point compression technique ultrasound of the lower extremity veins in patients presenting with:

• Lower extremity swelling and/or pain.
• Suspected pulmonary embolism, but clinically unstable or with other contraindications to obtaining CT of the chest or VQ scan.
• Pulseless electrical activity (PEA) as part of the assessment for a reversible cause.

How to Perform Ultrasound for DVT

• Patient Positioning: Position the patient as needed to maximize distention of the leg veins. An awake patient may be able to sit on the stretcher with the legs hanging off to the side. However, this manipulation may not be realistic in most instances when dealing with acutely ill patients. Elevating the head of the bed up to a 30-degree to 45-degree angle or positioning the stretcher in reverse Trendelenburg will also allow venous pooling in the lower extremities.⁶ Flex the patient’s leg at the knee and externally rotate the hip to allow the best exposure of the junction of the common, deep, and superficial femoral veins as well as the popliteal fossa. (See image 1, image 2.)
• Probe Selection: The preferred probe is the high-frequency linear array probe, because it provides better resolution, and its flat surface is ideal for achieving adequate compression. However, larger patients may require the increased penetration of the lower frequency curvilinear probe.
• Probe Positioning: Apply an adequate amount of ultrasound gel on the skin where the probe is located. Hold the probe in transverse position and perpendicular to the skin surface. Start the examination as proximally as possible—ideally at the inguinal ligament. Once the common femoral vein and artery are identified, scan distally until the great saphenous vein emptying into the common femoral vein can be seen. Proceed distally to the junction of the common femoral, superficial femoral, and deep femoral veins. Finally, place the probe in the popliteal fossa for visualization of the popliteal vein and artery.

  If there is difficulty differentiating artery from vein, color Doppler may be helpful, because it will demonstrate pulsatile arterial flow in comparison with the continuous flow of the vein. Pulse-wave Doppler can also be useful, because it demonstrates the peak and trough quality of arterial waveforms compared to the continuous undulating wave form of veins.

• Compression technique: At each point, apply firm compression perpendicularly to achieve complete collapse of the vein. The lumen of the vein must disappear completely in order to exclude the presence of a clot. (See image 3, image 4.) A clot may be seen as echogenicity within the lumen. However, in many instances the only evidence of a DVT will be the inability to compress the vein fully.
• Other signs of patency: Color-flow Doppler may reveal a persistent filling defect or thrombus in the color column of the lumen. (See image 5, image 6.) Squeezing the calf will produce the augmentation of venous flow to complete color filling of the lumen. However, using color Doppler and augmentation techniques is time-consuming and has not been shown to improve the detection of DVT significantly over venous compression.⁷
• Scanning the common femoral vein: The inguinal area is generally proximal to the junction of the great saphenous and common femoral veins. Overlying tissue or pannus may have to be lifted or moved to expose this most proximal site. Move the probe distally until you identify the great saphenous vein joining the common femoral vein medially and the common femoral artery coursing laterally. (See image 7.) Apply firm pressure downward to compress both the common femoral and proximal great saphenous veins. Although the great saphenous vein is a superficial vein, a clot identified within its proximal portion can propagate into the deep venous system and will require the same treatment as a deep vein thrombus. A patent vein will collapse completely.
• Scanning the proximal superficial femoral and deep veins: After compression of the common femoral and great saphenous veins, slide the probe distally to the femoral triangle, following the femoral vein. The image on the screen will show the common femoral vein medially and the superficial and deep femoral arteries laterally. (See image 8.) Continue to scan distally until you see the common femoral vein split into superficial femoral and deep femoral tributaries. Apply firm pressure downward to compress both veins.
• Scanning the popliteal vein: Place the probe behind the knee high in the popliteal fossa, where the popliteal vein and artery are located. The popliteal vein lies superficial to the artery. You may need to steady the outside of the knee with your nonscanning hand to stabilize the leg and facilitate compression. Apply firm pressure to collapse the popliteal vein. (See image 9, image 10.)

Pitfalls

• Failing to place the probe perpendicular to the skin to achieve direct pressure in compressing vessel walls.
• Mistaking an acute clot with chronic clot. Consider MRI to distinguish acute from chronic DVT.
• Assuming that visualization of the vessel lumen equals absence of DVT. An acute thrombus can be anechoic. Confirm patency by complete apposition of the anterior and posterior walls of the vessel.
• Technical difficulty in obese patients or those with significant lower extremity edema.
• Scanning the vessel longitudinally only. During compression the probe may slide off of the vessel wall and may lead to false negative results.
• Ilio-femoral DVT cannot be evaluated using ultrasound.
• Confusing a lymph node or Baker’s cyst with DVT. The transducer can be moved proximally and distally to identify the edges of the lymph node or cyst.
• Failure to understand the limitations of the three-point compression technique—calf vein thrombi and the rare segmental clot may be missed. Use Wells clinical prediction rule and d-dimer assays to determine your pre-test clinical probability. (See clinical algorithm.) If you have moderate to high suspicion for DVT but a negative initial screening exam, have the patient return within 1 week for a repeat ultrasound or perform contrast venography.⁸

For best results, optimize the patient position and scan the unaffected extremity for comparison. Consider scanning the legs of the patient presenting in cardiac arrest with pulseless electrical activity, because a dislodged clot resulting in a pulmonary embolism may direct emergent resuscitative care.

In summary, ultrasound is a useful diagnostic tool in the evaluation of patients presenting with signs and symptoms suggestive of a DVT. The three-point compression-technique ultrasound for lower extremity DVT can be performed by the emergency physician as a noninvasive tool to detect the presence of a noncompressible vein indicating a lumen-obstructing clot. Using ultrasound in the evaluation for DVT can decrease time to definitive care and length of stay in the emergency department.

References

1. Silverstein MD, et al. Trends in the incidence of deep vein thrombosis and pulmonary embolism: A 25-year population based study. Arch Int Med 1998; 158:585-93.
2. Lensing, et al. Detection of deep-vein thrombosis by real-time B-mode ultrasonography. N Eng J Med 1989; 320:342-5.
3. Birdwell, et al. The clinical validity of normal compression ultrasonography in outpatients suspected of having deep venous thrombosis. Ann Intern Med 1998; 128:1-7.
4. Blaivas, et al. Lower-extremity Doppler for deep vein thrombosis – can emergency physicians be accurate and fast? Acad Emerg Med 2000; 7:120-6.
5. Kline JA, et al. Emergency-clinician performed compression ultrasonography for deep venous thrombosis of the lower extremity. Ann Emerg Med 2008; 52:437-45.
6. Stone MB, Price DD, Anderson BS. Ultrasonographic investigation of the effect of reverse Trendelenburg on the cross-sectional area of the femoral vein. J Emerg Med 2006; 30:211-3.
7. Lensing, et al. A comparison of compression ultrasound with color Doppler ultrasound for the diagnosis of symptomless postoperative deep vein thrombosis. Arch Int Med 1997; 157:765-8.
8. ACEP Clinical Policies Committee. Clinical Policy: Critical issues in the evaluation and management of adult patients presenting with suspected lower-extremity deep venous thrombosis. Ann Emerg Med 2003; 42:124-35.