++
The clinical indications for performing a venous ultrasound examination are as follows:
+++
Suspicion of a Lower Extremity DVT
++
Virchow's triad—hypercoagulability, venous stasis, and vessel injury—is the main risk factor for developing a DVT. The pathophysiology behind the development of venous thrombosis is not as well understood as arterial thrombosis, although both involve similar elements of the coagulation cascade. Once thrombus has occurred, reorganization of the clot begins. This process allows clefts to form between the clot and the vein wall, beginning about 1 week after initial clot formation; this is thought to be when the risk of PE is greatest. Over the next several weeks, the clot may be lysed and recanalized, leaving a thickened intima.
++
Only about half of all patients with DVT have any noticeable signs or symptoms. Risk factors for DVT are listed in Table 17-1. The combination of risk factors, physical examination findings, and clinician judgment has been developed into a clinical prediction model (Table 17-2).8,9 This clinical prediction model is often combined with a high-sensitivity D-dimer assay to decide who should undergo ultrasound evaluation for DVT.
++
++
++
There are different views about how ultrasound should be used to assess for DVT. Historically, whole leg ultrasound has been performed in vascular laboratories. This is often referred to as duplex ultrasound, which combines compression ultrasound with multiple measurements using color and pulse wave Doppler. The entire leg is usually scanned, with measurements taken every few centimeters from the inguinal ligament down to and including the calf veins. This technique is time consuming, taking an average of 37 minutes to perform in one study.10
++
Another school of thought is to perform limited compression ultrasound concentrating on the common femoral vein and the popliteal vein. This technique seems best suited for emergency care providers because it can be performed rapidly at the patient's bedside and has been shown to be safe and effective. One study compared limited compression ultrasound to contrast venography in 220 patients clinically suspected of having DVT. Limited compression ultrasound was found to be 100% sensitive and 99% specific for clinically relevant DVT (popliteal and above).11 Numerous studies since then have confirmed the high sensitivity and specificity of a limited compression ultrasound technique.12–17 Others have raised a theoretical concern that there may be isolated DVT present in the superficial femoral vein that could be missed by this technique, but the preponderance of data do not support this belief.18
++
Several large studies have followed outcomes of patients at 3 and 6 months looking for venous thromboembolic events. They have all pointed to the safety of limited compression ultrasound for the diagnosis of DVT. A 2002 study performed a limited compression ultrasound on 1756 patients with suspected DVT.19 They combined this with a high-sensitivity D-dimer assay and limited repeat ultrasound in 1 week for patients with a positive D-dimer. Twenty-two percent of patients were diagnosed with a proximal DVT initially. Of patients with a negative initial ultrasound and D-dimer assay, only 6/828 (0.7%) had a venous thromboembolism at 3 months. Patients with a low pretest probability and a negative D-dimer assay had a 1.8% incidence of venous thromboembolism at 3 months, similar to previous validations of Wells criteria. Patients with a negative initial ultrasound and positive D-dimer had a 3% incidence of DVT in 1 week and an additional 2.1% at 3 months. At no point during this study were calf veins evaluated.
++
A 2008 study sought to directly compare a limited compression ultrasound evaluation plus D-dimer testing versus a whole leg duplex evaluation.3 It randomized 2098 patients to either approach, with death and DVT/PE at 3 months as the end point. In the limited compression pathway, 0.9% of patients had an untoward event at 3 months versus 1.2% in the whole leg group, which was considered equivalent. The whole leg approach diagnosed 20.4% proximal DVT initially, with 6% calf vein thrombosis; all were treated with anticoagulation. The limited compression ultrasound approach diagnosed 20.8% DVT initially. Of those with a normal initial ultrasound, 30.9% had a positive D-dimer and underwent repeat ultrasound after 1 week. No patients developed PE during this week and none were anticoagulated. After 1 week, an additional 5.5% of patients were found to have a proximal DVT. This study demonstrated that a limited compression ultrasound combined with 1-week repeat ultrasound in patients with a positive D-dimer was equivalent to a whole leg duplex study. This was presumably because the undiagnosed calf vein thrombi that will lead to proximal DVT tend to do so within 1 week. The limited compression ultrasound technique used in these studies included a single compression of the common femoral vein at the inguinal ligament, and two compressions of the popliteal vein, one at the midpoint of the popliteal fossa and the other at the distal popliteal fossa just proximal to its trifurcation.
++
Several studies have demonstrated that emergency medicine physicians can perform limited compression ultrasound in a few minutes with excellent results.12–17 A 2008 meta-analysis showed that emergency physicians can perform limited compression ultrasound for DVT with accuracy similar to radiology-performed ultrasound.20 In addition, a 2010 study demonstrated that emergency physicians who learned to perform simple compression ultrasound in just 10 minutes had 100% accuracy for diagnosing DVT compared to a whole leg duplex ultrasound performed by radiology.17
++
Most algorithms for the evaluation of DVT assume ultrasound is an expensive and time-consuming procedure, and so more emphasis is placed on clinical prediction models and D-dimer assays to exclude patients from requiring ultrasound21 (Figure 17-1). However, as emergency physicians become more adept at the technique, a limited compression ultrasound examination can be performed much more swiftly than a D-dimer assay. Using an ultrasound-first algorithm, all patients with clinically suspected DVT (whether low, moderate, or high) can have a limited compression ultrasound examination performed with the plan to have a repeat ultrasound performed in 1 week (Figure 17-2).
++
++
++
Limited compression ultrasound is often of greatest value to emergency providers on evenings, nights, weekends, and holidays when diagnostic imaging services are delayed or unavailable. Although calf vein thrombosis is not assessed with a limited compression ultrasound exam, managing patients based on the results of the limited compression exam has been shown to be safe and effective. A DVT will be diagnosed in about 10–20% of patients who are assessed with limited compression ultrasound, depending on how it is used. Patients who do not have a DVT may have incidental findings that lead to another diagnosis. About 15% of patients suspected of having DVT are eventually diagnosed with a Baker's cyst, knee effusion, or cellulitis, all of which can be visualized with ultrasound.
+++
Suspicion of an Upper Extremity DVT
++
Upper extremity DVT is thought to account for about 5% of all DVT cases.22 The most common causes of this disease process are malignancy, central venous catheters, and pacemaker wires. The vast majority of upper extremity DVTs is due to indwelling catheters and many occur in the subclavian vein. Other sources of DVT are the axillary and internal jugular veins. External jugular vein thrombosis is extremely rare.
++
While simple compression ultrasound works well in the lower extremities, the subclavian vein does not lend itself to compression. Therefore, excluding an upper extremity DVT depends on Doppler ultrasound and indirect confirmation of vein patency in a major venous segment. Although it has not been well studied, this suggests that ruling out an upper extremity DVT may be more difficult for less experienced providers. It may be prudent for less experienced providers to use upper extremity ultrasound to rule in the diagnosis of DVT, but not to try to rule it out. It is often straightforward to recognize a positive finding, so it is reasonable to do a brief point-of-care exam. However, patients with a negative point-of-care exam may need further evaluation with a comprehensive ultrasound exam or a CT scan, depending on the experience of the provider and the quality of the initial exam.
+++
Superficial Thrombophlebitis
++
Although data are lacking, upper extremity DVT is generally considered thrombosis involving the axillary and subclavian veins. Clot in the brachial and basilic veins is generally considered superficial thrombophlebitis, but some believe that this should be treated with anticoagulation. In the leg, the greater saphenous vein is considered a superficial vein, but some believe that thrombosis at this location also requires anticoagulation.7 Superficial venous thrombosis at other locations is considered to be of no significant risk for PE and is treated conservatively and without anticoagulation. On ultrasound, the appearance of superficial venous thrombosis is similar to that of a DVT with failure to compress the vein as the diagnostic criteria.