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Clinical Procedures > Radiology
Bedside Ultrasonography, Deep Vein Thrombosis
Article Last Updated: Jun 18, 2008
AUTHOR AND EDITOR INFORMATION
Section 1 of 12  
Author: Lars Grimm, BS, Yale University Medical School
Coauthor(s):
William C Manson, MD, Fellow in Emergency Ultrasound, Department of Surgery, Section of Emergency Medicine, Yale University School of Medicine
Editors: James Quan-Yu Hwang, MD, Attending Physician, Department of Emergency Medicine, Brigham & Women's Hospital; Clinical Instructor, Harvard Medical School; Mary L Windle, PharmD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy, Pharmacy Editor, eMedicine.com, Inc; Rick Kulkarni, MD, Medical Director, Assistant Professor of Surgery, Section of Emergency Medicine, Yale-New Haven Hospital
Author and Editor Disclosure
Synonyms and related keywords:
DVT, deep vein thrombosis, ultrasound examination, ultrasound exam, DVT exam, DVT examination, DVT ultrasound, deep vein thrombi, venous thromboembolism, deep venous thrombosis, blood clot, thrombus, U/S, ultrasound, lower extremity ultrasound, Doppler, PE, pulmonary embolism, pulmonary emboli
Venous thrombosis is a major cause of morbidity and mortality in the United States and a frequent cause of presentation in many emergency departments (EDs). The sequelae of deep vein thromboses (DVTs) range from the more common chronic venous stasis to the most serious pulmonary emboli (PEs).1 PEs have been described as one of the most common preventable causes of death, and approximately two thirds of PEs are estimated to originate in the lower extremities as DVTs. The rate of propagation from DVT to PE is estimated to range from 10-50%.2, 3 Treatments with anticoagulation or Greenfield filter placement are extremely effective if used early, thus underscoring the need for rapid diagnosis.
Compression ultrasonography has proven to be a highly sensitive and specific modality for the recognition of lower extremity DVTs without the need for radiation or contrast exposure.4, 5 Traditional lower extremity studies interrogate and review the entire lower extremity vasculature, are performed by an ultrasound technologist, and are read by a radiologist. These factors are not always available and have been shown to delay the time to diagnosis and potential treatment of a DVT by up to 2 hours.6, 7
EDs now use a modified 2-point compression technique that focuses on the highest probability areas, decreases the study time to less than 5 minutes, and provides similar sensitivity and specificity.8, 9 In patients with a clinically suspected DVT, a negative compression ultrasound may safely delay the need for anticoagulation therapy.10 The 2-point DVT compression examination has been assessed in multiple randomized controlled studies and is well accepted when used properly with pretest probability assessments.8, 11
The safety, ease of use, rapid time to diagnosis, low cost, and accessibility make bedside ultrasonography for DVT especially useful for emergency and critical care physicians.
Patients who have risk factors for deep vein thrombosis (DVT) or pulmonary embolism (PE), and in whom physicians suspect DVT or PE, should have workups that include, but are not necessarily limited to, bedside compression ultrasonography.
- Absolute contraindications: No absolute contraindications exist.
- Relative contraindications: If the clinical suspicion and pretest probability for a pulmonary embolism (PE) are high enough that a spiral CT with intravenous contrast or V/Q (ventilation/perfusion) scan is warranted, then ultrasonography should not delay such studies or any further treatment goals. (Click here to complete a Medscape CME activity on the use of multislice CT in the diagnosis of PE.)
- Portable bedside ultrasound machine with a high-resolution linear transducer
- Ultrasound gel
The patient should be supine with the leg in question exposed up to the inguinal ligament. Bedside ultrasonography for deep vein thrombosis (DVT) is performed in 2 principal positions, one for each area of examination. The following are ideal positions. Patient status and cooperativity, however, ultimately determine what kind of positioning is possible. Ideally, 30-40 degrees of reverse Trendelenburg facilitates the examination by increasing venous distention.
- When examining the femoral vein, the patient should be supine with the hip externally rotated and flexed.
Patient positioning when assessing the femoral vein. - When examining the popliteal vein, the patient needs to expose the popliteal fossa on the posteromedial aspect of the knee. The patient can either dangle the leg off the edge of the bed or bend the knee and externally rotate the hip. If necessary, the patient can also be rolled onto his or her side or into the prone position.
Patient positioning when assessing the popliteal vein.
Preparation - Set up the portable ultrasound machine at the patient's bedside, with the linear transducer set at a frequency of 5.0-7.0 MHz.
- Expose the patient’s entire leg.
- By convention, emergency physicians scan in an abdominal orientation with the probe marker pointed toward the patient’s head or right side. During the bedside ultrasonographic examination for deep vein thrombosis (DVT), the emergency physician maintains this convention, ie, the probe marker points toward the patient’s right. In terms of orientation, remember that the top of the viewing screen is always where the transducer is touching the patient.
Lower extremity vascular anatomy.
Femoral vein - Position the patient as noted above for examination of the femoral vessels. The study begins with an examination of the common femoral vein just distal to the inguinal ligament. The femoral vessels are located just inferior to the inguinal ligament and approximately midway between the pubic symphysis and the anterior superior iliac spine. The femoral artery is usually palpable. This is the initial point of examination.
- Apply gel to the transducer, the patient’s leg, or both, and position the transducer transversely, just distal to the inguinal ligament. Remember, the indicator on the probe should point toward the patient’s right. In this transverse view, the vein is imaged in cross-section.
Probe positioning for assessment of the femoral vein. - Drag or fan the transducer in a cephalad or caudad direction until the junction of the common femoral vein and the greater saphenous vein can be visualized. The common femoral artery is lateral to the common femoral vein.
Ultrasonographic image of femoral vessels without compression. - Using the transducer, apply direct pressure to completely compress the vein.
- If the vein compresses completely, then a DVT at this site can be ruled out.
- Be sure that enough pressure is being applied and being applied evenly. Apply enough pressure so that slight deformation of the artery is noticeable.
- If the vein is still not completely compressible, a DVT is present.
Ultrasonographic image of femoral vessels with compression. - Complete compression of the vein rules out a DVT, while the inability to completely compress the vein rules in a DVT. Thus, compressibility is the rule in/rule out criterion for DVT on ultrasound. (See Results below for more details.)
- Compressibility must be present in both the femoral veins and the popliteal vein. Sometimes, the angle of the transducer may need to be adjusted in order to completely compress the vein. The greater saphenous vein is a superficial vein. A clot in the greater saphenous vein near its junction with the common femoral vein, however, can easily propagate.
- The examination of the common femoral vein should extend from 2 cm proximal to 2 cm distal to the intersection of the common femoral and greater saphenous veins.
- Distal to the greater saphenous vein, the common femoral vein splits into the deep and superficial femoral veins. Despite its name, the superficial femoral vein is indeed a deep vein. Once the physician confirms collapse of both the deep and superficial femoral veins, he or she may move on to the popliteal vein.
Popliteal vein
- Position the patient as noted above for examination of the popliteal vessels.
- Again, apply gel to the transducer, the patient’s leg, or both, and position the transducer transversely in the popliteal fossa, with the probe marker directed toward the patient’s right.
Probe positioning for assessment of the popliteal vein. - Drag or fan the transducer in a cephalad or caudad direction until the superficial popliteal artery and vein are visible. The popliteal vein is usually posterior to the popliteal artery. Given the posterior approach of the probe (transducer face is placed in the popliteal fossa), however, the vein appears more superficial (closer to the transducer face) than the artery. The popliteal vessels are compressed more easily, so reducing probe pressure may help visualize the veins.
Ultrasonographic image of popliteal vessels with clot. - The examination should include the distal 2 cm of the popliteal vein and the proximal aspects of its trifurcation into the anterior tibial vein, the posterior tibial vein, and the peroneal vein. Anatomic variability is not uncommon, and the popliteal vein is often seen dividing into the anterior and posterior tibial veins with the peroneal vein then splitting off from the posterior tibial vein.
Doppler ultrasonography
- Although not a formal component of the focused lower extremity compression examination for DVT, Doppler ultrasonography may be useful to help determine anatomic orientation and to further interrogate potentially misleading structures. Information obtained from Doppler ultrasonography alone, however, does not yield definitive evidence regarding clot presence.
- Doppler assesses the direction, velocity, and pattern of blood flow, with venous and arterial vessels demonstrating characteristic patterns. Normal venous vasculature should show venous flow at baseline, augmentation of flow with calf compression, and phasic respiratory ventilation with increased flow during expiration. In general, augmentation helps assess for obstruction distal to the probe, while respiratory variation helps assess for obstruction proximal to the probe (ie, iliac veins and inferior vena cava).
- Vessel filling defects may indicate on-site or upstream flow obstruction.
- Cysts or other fluid cavities are devoid of flow.
- Lymph nodes demonstrate dense, high vascularity.
Results
- For the focused DVT compression ultrasonographic examination, complete compressibility is the only absolute criterion to rule out DVT.
- Lack of compressibility is the only absolute criterion to rule in DVT. Documentation of the most proximal aspect of the clot is important to assess progression or regression of the clot after intervention.
- Direct visualization of a clot and Doppler flow abnormalities may suggest a DVT and, if clinically appropriate, may justify serial scans. Alone, however, they are limited in terms of their ability to definitively diagnose a DVT.
Ultrasonographic image of a deep vein thrombosis (DVT).
- Be sure the veins fully compress. Be sure to apply pressure evenly along the transducer face (perpendicular to skin surface). Avoid pressing at an angle, as this may result in uneven compression and a false positive finding.
- In patients who are obese, decreasing the transducer frequency to 3.5-5 MHz increases the depth of penetration and can assist the examiner. Overall image quality, however, is reduced.
- If no vein is visible at the appropriate anatomic sight, the transducer may already be compressing the vein. Reduce the amount of pressure being applied and reexamine the area of interest.
- Care must be taken to not over-interpret vessel echogenicity as clot. Both normal blood flow and vessel artifact can appear hyperechoic.
- Cysts, especially Baker cysts, are commonly encountered in the popliteal region. These can be readily distinguished by their confluence with the joint space and their lack of flow on color flow Doppler ultrasonography.
- Lymph nodes are particularly common in the femoral region and can be identified by their superficial location, their characteristic appearance (hyperechoic center with hypoechoic rim), and their high vascularity on color flow Doppler ultrasonography.
Ultrasonographic image of a lymph node. - Duplicate popliteal and femoral veins are not uncommon. Special attention must be paid to rule out a DVT in patients with a duplicate vessel because the potential decrease in flow velocity may increase the risk for clot development.12
- Utilizing the dual-image picture or split-screen option before and after compression may make comparison easier. In addition, the split-screen option may be useful in hospitals that use still images for documentation.
- If the examination site is wounded, the ultrasound transducer may be covered with a sterile probe cover with gel applied to both the inside and the outside of the cover.
- If the examining physician is unable to perform an adequate examination secondary to patient body habitus, patient compliance, or skill limitation, the patient requires a formal ultrasonographic study. In addition, if the study results are indeterminate, then a formal ultrasonographic study should be obtained.
Bedside ultrasonography for assessment of deep vein thrombosis (DVT) poses no significant complications. No evidence exists for the potential propagation of clot through leg manipulation or vessel compression.9
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Patient positioning when assessing the femoral vein. |
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Patient positioning when assessing the popliteal vein. |
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Probe positioning for assessment of the femoral vein. |
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Probe positioning for assessment of the popliteal vein. |
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Ultrasonographic image of femoral vessels without compression. |
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Ultrasonographic image of femoral vessels with compression. |
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Ultrasonographic image of popliteal vessels with clot. |
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Ultrasonographic image of a deep vein thrombosis (DVT). |
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Bedside Ultrasonography, Deep Vein Thrombosis excerpt Article Last Updated: Jun 18, 2008
Topic originally published: Jun 18, 2008
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