July 2010

By Phillips Perera, MD, RDMS, FACEP, Thomas Mailhot, MD, RDMS, and Diku Mandavia, MD, FACEP, FRCPC

Rapid ultrasound in Shock: the rush protocol

EVALUATION OF THE "pipes"
Last month, we began our discussion of the final part of the RUSH protocol, the evaluation of the “pipes.” In that installment, we focused on ultrasound examination of the aortic artery. This month, as we conclude our series on RUSH, we continue our discussion of the use of bedside ultrasound to evaluate the “pipes”—specifically, to evaluate the veins for deep vein thrombosis (DVT). In addition, we demonstrate the utility of this exam in the hands of the emergency physician.

ULTRASOUND DETECTION OF LEG DVT
Bedside ultrasonography for the detection of DVT of the leg is an advanced imaging study, but the necessary techniques are readily learned by emergency physicians who have an interest in sonography. The bedside exam comprises a two-point limited evaluation of the deep veins of the leg, with special attention to the proximal femoral vein and the popliteal vein. Elements of the more comprehensive, radiologist-performed exam are mentioned later in this article. Research has shown that the abbreviated bedside ultrasound evaluation of the leg retains excellent sensitivity in the diagnosis of DVT, while allowing for exam expediency.¹

Veins have valves interspersed along their course, and most DVTs form in the areas behind the valves of the calf veins, where blood flow is often turbulent. Three smaller calf veins join together to form the popliteal vein, which lies just posterior to the knee joint in the popliteal fossa. While imaging of the calf veins can be difficult due to the small caliber of the vessels, the popliteal vein can be readily seen on ultrasound exam. Therefore, the popliteal vein, with the probe placed at the popliteal fossa, is the most inferior position for the bedside exam, as well as for most standard radiologist-performed DVT exams. In the popliteal fossa, the popliteal vein is seen posterior to the paired popliteal artery (Figure 1). The vessel should be imaged throughout its course in the popliteal fossa, usually for a distance of 3 to 5 cm. The popliteal vein then continues up the leg to form the superficial femoral vein in the thigh. The common femoral vein, which can be easily imaged at the superior aspect of the thigh, is formed by the coalescence of the superficial and deep femoral veins. The saphenous vein, a superficial vein of the leg, can often be seen draining into the common femoral vein. In the superior thigh, the common femoral vein will be seen just medial to the common femoral artery (Figure 2). The femoral vein should be imaged for 4 to 6 cm beginning high in the leg, just below the inguinal ligament, moving inferiorly through its junction with the saphenous vein (Figure 3), down to the level of bifurcation into the superficial and deep femoral veins.

Conclusion
With use of modern high-resolution ultrasound machines, bedside sonography can often image the actual clot, although the appearance may vary with the age of the clot. Fresh clot can appear more echogenic, or bright, on exam. Additional ultrasound techniques, such as augmentation of venous flow on color Doppler exam with compression of the calf and respiratory variation, may be included in a comprehensive, radiologist-performed exam. However, these elements do not substantially enhance the accuracy of the standard compression exam for detection of DVT. Figure 4 illustrates the utility of compression techniques in ultrasonography of the femoral vein to demonstrate a DVT of the common femoral vein; the image was taken with direct probe pressure over the vein.

Reference 1. Bernardi E, Camporese G, Büller HR, et al. Serial 2-point ultrasonography plus D-dimer vs whole-leg color-coded Doppler ultrasonography for diagnosing suspected symptomatic deep vein thrombosis: a randomized controlled trial. JAMA. 2008;300(14):1653-1659.