Ultrasound Leadership Academy: Lower Extremity DVT
Michael Macias
By Michael Macias
Welcome to the Ultrasound Leadership Academy (ULA) summary blog series. This week, we discuss ultrasound in early pregnancy. The ULA is essentially an online advanced ultrasound education experience put on by the team from Ultrasound Podcast which brings cutting edge learning to emergency medicine personnel through a variety of interactive platforms including video lectures, google hangouts with experts, simulation, live conferences and real time scanning with a pocket-sized ultrasound device known as a Vscan.
Over the next year I will be posting summaries of the key learning points from my experience. If you want to learn more about the program you can visit Ultrasound Leadership Academy or Ultrasound Podcast to see more from the hosts of this awesome program.
Introduction
The annual incidence of deep venous thrombosis (DVT) is in the range of 300,000-600,000 leading to 60,000-100,000 deaths from pulmonary embolism each year. The significant mortality associated with DVT warrants effective diagnosis however given that anticoagulation is not without risk, accuracy is of upmost importance.
Working in the emergency department, we continue to be a front line for patients presenting with concern for DVT and have specifically appreciated a rise in presentation for a "rule out DVT" as the public has become hypervigilant regarding subtle signs and symptoms. While useful to have general public awareness, this has led to significant increase in testing and potentially over treatment of small isolated calf (distal) DVTs where evidence of both associated morbidity and utility of treatment is not well known.
As we begin to see more patient who need to be ruled out for a DVT, we have to establish a clear method for risk stratification and decide who needs an ultrasound and who does not. Currently, all of these patient's are being whisked off to the vascular lab for duplex studies, however there is growing literature to support beside compression ultrasonography by emergency physicians as the initial study. Multiple studies have demonstrated that this approach is both sensitive and specific for diagnosis of DVT and decreases ED length of stay.
Anatomy
Unlike a formal duplex ultrasound which involves a 45 minute scan of the entire lower leg venous system, bedside compression ultrasonography in the ED is focused on two specific regions, the femoral region and the popliteal region. Now there is a significant amount of evidence to support a "two point" compression test which focuses on the femoral vein at the take off of the saphenous vein, and the popliteal vein just posterior to the knee, as the majority of DVTs occur around these two areas. However, there is growing evidence to suggest that single compression sites at the femoral and popliteal veins may be missing a few proximal isolated DVTs.
That being said a regional approach which is a slight modification of the two point compression method seems reasonable. This merely involves a few more minutes of scanning. You will need to examine the femoral region, from the take off of the saphenous vein, down through the proximal superficial femoral and deep femoral veins. You will also examine the popliteal region, from the popliteal vein down through the take off of the anterior tibial vein.
Technique
Probe: Linear, high frequency (Though if you patient is very large you can attempt to use a curvilinear probe)
Positioning: Have the patient lie supine with a sheet covering their groin region. Externally rotate and flex the hip slightly to expose the femoral region. When examining the popliteal region, the knee should be flexed at around 45 degrees.
Compression: As we discussed above you will be scanning both the femoral and the popliteal region. In these regions you will be performing direct compression of the vein to ensure there is no clot. In order to confidently rule out clot in the vein you need to be sure that you are obtaining complete compression of the vein and occlusion of the lumen. Essentially your will see the vein winking back at you, letting you know that there is no clot to be found. The questions always comes up about how hard to push and an easy measure to use is arterial compression. If you are pushing hard enough that the artery is starting to compress then you are compressing sufficiently and if your vein lumen is still patent then likely you are seeing a clot. If you are having trouble visualizing the vessels you can use color doppler however for the most part this is not necessary and may cause confusion.
The only difference between the regional compression versus the single point compression is instead of a single compression, you will compress the vein along the entire region of interest, both in the femoral region and the popliteal region, following along the vein of interest in a transverse plane. Refer to the diagram above a second time to review the anatomy of the regions to compress.
Clinical Approach
We always have to take into account pre-test probability and consider the likelihood a patient may have a particular disease prior to any testing based on their clinical picture and their risk factors. For DVT we have the Wells score which helps us to predict which patient's are more likely to have a DVT and which probably don't require much testing.
From ULA Course DVT Clinical Algorithm
How your algorithm specifically works will highly depend on your clinical setting and the resources you have available but the main point to highlight is that your ultrasound as well as other tests such as the d-dimer need to be placed in context of the patient's risk for having a DVT. Many low risk patients can be ruled out without even having to perform an ultrasound and high risk patients who have a negative ultrasound initially should still have a repeat formal ultrasound performed since their risk is so high that a single exam does not sufficiently rule out a DVT. An alternative algorithm proposed by Dr. Matt Dawson is seen below and focuses on the bedside ultrasound to help rapidly dispo low risk patients without the need for a d-dimer. One algorithm is not particularly better than the other as long as you are incorporating ultrasound into your practice just as you would any other lab test or exam in a bayesian manner.
From ULA Course DVT Modified Clinical Algorithm
Controversy
I am sure you are wondering, "What about those distal isolated clots that we always find?" Well the evidence for isolated clots in these distal lower leg veins is not great and it seems that even the hematologic community is beginning to advocate for a "don't look, don't tell policy." The risk of PE from these isolated clots is not well known and many surveillance studies appear to overestimate the risk. One study, the CALTHRO study, in which the presence of isolated distal DVT was kept blind to patients, and doctors in charge, found the risk of PE to be 1.6% at 3 months.
We all know that if we see a clot in the distal lower extremity venous system and tell a patient they have a clot that regardless of the actual risk of morbidity or proximal extension, they are going to want treatment with anticoagulation. Looking at the small amount of literature we do have, patients with distal clots who have proximal extension or PE have risk factors that we associate with DVT anyway. Therefore even looking at this topic from the view of the hematology literature, in the right patients it is reasonable to perform our two region compression exam without examination of the distal vessels. Below is an algorithm proposed by Dr. Gualtiero Palareti, an Italian hematologist, in a recent review on the evidence and clinical management of isolated distal deep vein thrombosis which can be found here.
Diagnostic/Therapeutic Algorithm for IDDVT From How I treat isolated distal deep vein thrombosis; CUS = Compression Ultrasound; IDDVT = Isolated Distal DVT
Continue Learning
DVT Lecture at Emergency Ultrasound Teaching
THAT'S IT FOR THIS WEEK
If you are interested in learning more about the ULA learning experience, visit their website below:
All images are courtesy of the ULA online video course unless otherwise stated. More on DVT ultrasound can be found in "Introduction to Bedside Ultrasound," Volume 1 & 2, from Dr. Mallin and Dr. Dawson. If you are interested in purchasing these ebooks for less than $1, visit Ultrasound Podcast Consumables.
References
- Crisp et al. Compression ultrasonography of the lower extremity with portable vascular ultrasonography can accurately detect deep venous thrombosis in the emergency department. Ann Emerg Med. 2010 Dec;56(6):601-10.
- Kory et al. Accuracy of ultrasonography performed by critical care physicians for the diagnosis of DVT. Chest. 2011 Mar;139(3):538-42.
- Blaivas et al. Lower-extremity Doppler for deep venous thrombosis--can emergency physicians be accurate and fast? Acad Emerg Med. 2000 Feb;7(2):120-6.
- Theodoro et al. Real-time B-mode ultrasound in the ED saves time in the diagnosis of deep vein thrombosis (DVT). Am J Emerg Med. 2004 May;22(3):197-200.
- Adhikari et al. Isolated Deep Venous Thrombosis: Implications for 2 Point Compression Ultrasonography of the Lower Extremity. Ann Emerg Med. 2014 Nov 20.
- Palareti et al. Evolution of untreated calf deep-vein thrombosis in high risk symptomatic outpatients: the blind, prospective CALTHRO study. Thromb Haemost. 2010 Nov;104(5):1063-70.
Gualtiero Palareti. How I treat isolated distal deep vein thrombosis (IDDVT). Blood: 2014 Mar; 123 (12).
Singh et al. Early follow-up and treatment recommendations for isolated calf deep venous thrombosis. J Vasc Surg. 2012 Jan;55(1):136-40.
Schwarz et al. Therapy of isolated calf muscle vein thrombosis: a randomized, controlled study. J Vasc Surg. 2010 Nov;52(5):1246-50. doi: 10.1016/j.jvs.2010.05.094. Epub 2010 Jul 13.