US Probe: Pearls and Pitfalls for Point-of-Care Ultrasound Evaluation of Deep Vein Thrombosis
- Jul 11th, 2019
- Jeremy Carter
Author: Jeremy Carter, DO RVT (Chief Resident, Rutgers New Jersey Medical School) // Editors: Stephen Alerhand, MD (@SAlerhand; Assistant Professor, Rutgers New Jersey Medical School); Brit Long, MD (@long_brit); and Manpreet Singh, MD (@MprizzleER)
Several prior studies have examined the role of point-of-care ultrasound (POCUS) for the evaluation of suspected acute lower extremity deep vein thrombosis (DVT). To begin with, when performed by emergency physicians, POCUS has been shown to decrease emergency department (ED) time to disposition when compared to scans performed by imaging specialists.1 In addition, 2-point (common femoral and popliteal vein) and 3-point (2-point plus sapheno-femoral junction) compression have been shown to be very accurate when compared to both ultrasound of the full lower extremity venous system (performed by trained imaging specialists) and CT venography.2-9 However, in not scanning the length of the femoral and deep femoral vein, about 6% of DVT’s may be missed.10 Many studies also cite the need for a significant amount of training and practice to become proficient in these exams.2-5,8
During the years before medical school, I trained and worked as a vascular sonographer. This has given me additional insight into the potential obstacles and pitfalls encountered when attempting to accurately rule out lower extremity DVT at the bedside. Colleagues have shared their clips and experiences with me, and these have demonstrated several themes. Below are five potential pitfalls accompanied by teaching pearls that may be of assistance:
The groin area is sensitive to compression due to pain, feeling ticklish, or both. As a result, the patient may hold their breath and perform Valsalva, making it difficult to compress the vein. This gives the false appearance of a non-compressible right common femoral vein.
Contrast this with a “true positive” non-compressible femoral vein secondary to an acute DVT.
Instruct the patient to take a deep inhalation and then exhale. Time your compression to exhalation.
See the fully compressible right common femoral vein when timing compression with exhalation.
The femoral vein in the mid-to-distal thigh dives through Hunter’s Canal. The vessel’s depth makes it difficult to visualize and compress, giving the false appearance of a DVT.
Have the patient straighten the leg and internally rotate the hip, from the usual externally rotated position. Slide the transducer anteriorly on the patient’s thigh, angling straight down towards the bed. Place the free non-scanning hand under the thigh, and squeeze up towards the transducer for easier compression.
See compression of the distal right femoral vein.
There are multiple tendinous and ligamentous structures at the medial and lateral border of the popliteal fossa. This can lead to difficulty compressing the popliteal vein.
Contrast this with an actual thrombus in the popliteal vein.
Slightly change the orientation and compress from a different angle. Use the free hand to compress the knee from above.
See the proper compression of the popliteal vein.
Poor quality images.
Adjust the depth so that the vein to be imaged lies in the center of the screen. If the machine allows, adjust the focus to about the center or just below the vein to be imaged. Use the curvilinear transducer as an alternate option.
Making incorrect assumptions without using adjunctive or confirmatory techniques.
Turn the transducer to view the vessel in long-axis. Look for internal echoes from this other perspective.
In addition, insonate the vessel with color Doppler and pulsed wave Doppler .
The Doppler equation includes the cosine of the angle between the ultrasound beam and the flow in a vessel. If the angle between the ultrasound beam and blood flow is 90 degrees, no flow will be seen, because the cosine of 90 degrees is zero.
Thus, for the best Doppler signal, orient the vessel in long-axis and rock the transducer to make the vein cross the screen at an angle instead of horizontally across, so that the sound waves no longer insonate the vessel at a perpendicular angle.
If feasible on your machine, “steer” or change the orientation of the color box to keep the angle between the US beam and vessel as small as possible.
By rocking the transducer superiorly or inferiorly, the transverse orientation of the vessel can also be evaluated using color Doppler.
- 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). The American Journal of Emergency Medicine. 2004;22(3):197-200. doi:10.1016/j.ajem.2004.02.007
- Frazee BW, Snoey ER, Levitt A. Emergency Department compression ultrasound to diagnose proximal deep vein thrombosis. The Journal of Emergency Medicine. 2001;20(2):107-112. doi:10.1016/s0736-4679(00)00302-4.
- Crisp JG, Lovato LM, Jang TB. Compression Ultrasonography of the Lower Extremity With Portable Vascular Ultrasonography Can Accurately Detect Deep Venous Thrombosis in the Emergency Department. Annals of Emergency Medicine. 2010;56(6):601-610. doi:10.1016/j.annemergmed.2010.07.010.
- Crowhurst TD, Dunn RJ. Sensitivity and specificity of three-point compression ultrasonography performed by emergency physicians for proximal lower extremity deep venous thrombosis. Emergency Medicine Australasia. 2013;25(6):588-596. doi:10.1111/1742-6723.12155.
- Mulcare MR, Lee RW, Pologe JI, et al. Interrater reliability of emergency physician-performed ultrasonography for diagnosing femoral, popliteal, and great saphenous vein thromboses compared to the criterion standard study by radiology. Journal of Clinical Ultrasound. 2016;44(6):360-367. doi:10.1002/jcu.22338.
- Fulvio P, Dentali F. Accuracy of real time B-mode ultrasonography in the diagnosis of deep vein thrombosis in hip surgery. Thrombosis Research. 1991;61:70. doi:10.1016/0049-3848(91)90542-5.
- Burnside PR, Brown MD, Kline JA. Systematic Review of Emergency Physician–performed Ultrasonography for Lower-Extremity Deep Vein Thrombosis. Academic Emergency Medicine. 2008;15(6):493-498. doi:10.1111/j.1553-2712.2008.00101.x.
- Shiver SA, Lyon M, Blaivas M, Adhikari S. Prospective comparison of emergency physician–performed venous ultrasound and CT venography for deep venous thrombosis. The American Journal of Emergency Medicine. 2010;28(3):354-358. doi:10.1016/j.ajem.2009.01.009.
- Pedraza García J, Valle Alonso J. Comparison of the Accuracy of Emergency Department-Performed Point-of-Care-Ultrasound (POCUS) in the Diagnosis of Lower-Extremity Deep Vein Thrombosis. J Emerg Med. 2018 May;54(5):656-664.
- Adhikari S, Zeger W, Thom C, Fields JM. Isolated Deep Venous Thrombosis: Implications for 2-Point Compression Ultrasonography of the Lower Extremity. Annals of Emergency Medicine. 2015;66(3):262-266. doi:10.1016/j.annemergmed.2014.10.032.
Special thanks to Mikhail Blyakher MD and Michael Anana MD for assistance in the production of this post’s media.