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Student Corner: Ultrasound Approach to DVT

January 28, 2016

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Deep venous thromboses are thought to occur in as many as 1 in 1000 people annually1, although many instances never present to urgent care or emergency room settings. When a patient does make it to the ER, the most common presentation is a swollen, tender lower extremity. Although there are many things on the differential, the emergency room physician must rule out DVT because of the potential risk of subsequent pulmonary embolism.

Ultrasound has become the go-to method for evaluation of DVT. In the ER setting, the limited compression ultrasound technique is most widely used due to the ease and speed at which it can be performed. A duplex scan with color Doppler can be useful in other scenarios, but these evaluations can take up to an hour, require a skilled technician, and have not been shown to be any more accurate in detection of proximal DVTs compared to limited compression ultrasound2.

Limited compression ultrasound frequently targets two main locations for DVTs: the common femoral vein and the popliteal vein. The ultrasound is typically done using the linear or vascular probe (6-10 MHz), which was designed for imaging vessels, but has the added benefit of being flat, which helps with uniform compression when assessing for DVTs.

During the ultrasound exam, is important for the leg to be in a dependent position, which will allow for ideal assessment during compression. This can be achieved by putting the patient in reverse Trendelenburg, or by having them partially seated with 30 degrees of hip flexion.

Start by palpating for the femoral artery in the groin crease, which will allow you to easily locate the common femoral vein, which lies just medially. Hold the probe in transverse orientation, so that you can see the cross-sections of both the artery and vein. Follow the vessels distally, looking for the common femoral vein to bifurcate into the superficial and deep femoral veins approximately 6 cm from the inguinal ligament. Look closely at the branch points, as these are common areas for thrombi to form.

Lower_Ext_Vasc

(Image courtesy of David Darling)

*A note about the nomenclature: the superficial femoral vein is actually a deep vein, and thrombi are much more common in the superficial femoral compared to the deep femoral vein. The superficial femoral vein is sometimes referred to as simply the femoral vein.

Follow the superficial femoral vein as it becomes the popliteal vein, and then passes behind the knee. Scan about 5-7 cm distal to the popliteal crease – thrombi distal to this are very unlikely to generate threatening emboli. The vein should be just superficial to the artery as you follow the popliteal vein and artery near the knee.

As you are conducting the ultrasound you will apply pressure approximately every centimeter with the probe. As pressure is applied, the vein should start to compress, with the anterior and posterior walls eventually coming into contact. The pressure needed to completely collapse the vein should not disrupt the architecture of the femoral artery. If the vein does not completely collapse, or if the pressure necessary becomes so great that the artery becomes distorted as well, there is likely a thrombus in that segment of the vein. Scan proximally and distally from that point to examine the extent of the thrombus.

Below are two ultrasound images of the superficial femoral vein (blue) and femoral artery (red). The image on the left is without compression. The artery is superficial to the vein, and the lumen of the femoral vein is slightly larger than the artery. These characteristics help with identification. The image on the right shows the same vessels during compression with the ultrasound probe. The artery is now very ovoid and almost flat, while the vein is still round, and the lumen shows some, which represents a thrombus.

DVT Baseline vs Compress

Before (left) and after compression (right)


Illustration courtesy of David Darling

Ultrasound images courtesy of Dr. Kenneth Kelley


References:

  1. Silverstein MD, Heit JA, Mohr DN, Petterson TM, O’Fallon WM, Melton LJ 3rd.
    Trends in the incidence of deep vein thrombosis and pulmonary embolism: a 25-year population-based study. Arch Intern Med.1998;158:585-593.
  2. Lensing AW, Prandoni P, Brandjes D, Huisman PM, Vigo M, Tomasella G, Krekt J, Wouter Ten Cate J, Huisman MV, Büller HR. Detection of deep-vein thrombosis by real-time b-mode ultrasonography. N Engl J Med.1989;320:342-345.
  3. Dean, AJ, Ku, BS(2008). Deep Venous Thrombosis. Retrieved from http://www.sonoguide.com/dvt.html
  4. Theodoro D, Blaivas M, Duggal S, Snyder G, Lucas M. Real-time B-mode ultrasound in the ED saves time in the diagnosis of deep vein thrombosis (DVT). Am J Emerg Med.2004;22:197-200.

Author: Mitchell Datlow

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Aortic dissection…

June 16, 2014

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This patient presented with chest pain radiating to the back:

AD CXR 1

 

The patient’s initial chest X-ray shows a widened mediastinum and an indistinct aortopulmonary window.  CT showed:

AD CT 1 AD CT 2 AD CT 3

This patient has an aortic dissection.  There are two different classification systems for aortic dissection:  Stanford and DeBakey (1).

Stanford Criteria:

  • Type A:  The dissection flap involves the ascending aorta
  • Type B:  The dissection commences distal to the left sub-clavian artery

DeBakey Criteria

  • Type I: The dissection flap involves the ascending aorta and descending aorta
  • Type II:  The dissection flap involves the ascending aorta only
  • Type III:  The dissection flap involves the descending aorta only

This is a Stanford Type A and a Debakey Type I because it involves the ascending aortic arch all the way to the iliac bifurcation.

What is important to remember (besides the number for a cardiothoracic surgeon)?  If the flap involves the ascending aorta these are usually managed operatively. Descending dissections are many times managed medically (1).

Besides rupture, the main problem with aortic dissection is perfusion to various organs.  Virtually every solid organ can be affected depending on the spacial characteristics of the dissection flap.  In this case the last image clearly shows that the right kidney is not perfused, indicating that the dissection flap has occluded the right renal artery.  The kidneys and bowel are the most common organs to develop ischemia.

Author:  Russell Jones, MD

Image Contributor:  Jay Williams, MD

References

  1. Broder JS.  Diagnostic Imaging for the Emergency Physician.  Elsevier, 2011.
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