The LE should be exposed from the inguinal region to the popliteal fossa. The leg should be externally rotated and the knee slightly flexed (Fig. 13.4). On the rare occasion when a barrier, such as a dressing, is obscuring the ability to perform an ideal exam, consider removing the barrier and using a sterile probe cover to create a clean interface between the probe and the patient’s skin.

A high-resolution ultrasound machine with grayscale imaging and a high-frequency 7–10-MHz linear probe are needed for the examination. Place the transducer just below the inguinal ligament, holding the transducer in a transverse orientation with the indicator pointing toward the operator’s left. The common femoral vein and artery should be immediately visible where the vein is typically more medial than the artery (Fig. 13.5). Apply downward pressure until the vein completely collapses to the extent that the walls touch each other. When adequate pressure is applied (demonstrated by visualizing simultaneous deformity of the artery with downward pressure) and the vessel lumen does not collapse or if echogenic material is noted within the vein, the study is diagnostic for a thrombus. If the walls of the vein are seen to completely collapse, pressure is released, and the probe is moved distally by 1–2 cm to find the junction of the greater saphenous vein with the common femoral vein. The greater saphenous vein will be seen entering the common femoral vein medially. When compressed, the lumen of both the greater saphenous and the common femoral veins should completely disappear (Fig. 13.6).

After inspecting the greater saphenous vein, the next important landmark is the bifurcation of the common femoral artery into the superficial and deep femoral arteries, adjacent to the accompanying common femoral vein (Fig. 13.1). The common femoral vein then divides into the deep femoral and superficial femoral veins (Fig. 13.7). In this region distinguishing artery from vein may be difficult, especially with larger legs. Use of pulse wave and/or color Doppler is extremely helpful in distinguishing the superficial and deep arteries from the veins. Next, the superficial and deep femoral veins are evaluated in 1–2 cm segments until the deep femoral vein disappears, leaving the superficial femoral vein to be followed as distally as possible.

With the knee flexed 45°, place the transducer in the popliteal fossa to begin examination of the lower leg and popliteal region. After the popliteal artery and vein are identified, and compression of the vein is demonstrated (Fig. 13.8), move down the leg slightly until the veins just distal to the trifurcation of the popliteal vein are visualized and compressed. Though identification of a DVT in the calf veins (distal to the popliteal vein) does not mandate automatic treatment, knowledge of its presence warrants close follow-up with repeat CUS. The consideration to initiate full dose anticoagulation must be carefully weighed in high-risk ICU patients found to have a distal DVT [20].

Once transverse imaging is complete, longitudinal views of the veins serve as a quick check and balance. Returning to the common femoral vein and rotating the ultrasound probe 90°, scan through the common femoral, superficial femoral, and popliteal veins in the longitudinal plane to ensure no intraluminal thrombus is seen. Just like with transverse views, compress the vessels with the probe to ensure that the vessels collapse completely. If thrombus was previously found in the transverse plane, the longitudinal view helps visualize the extent of intraluminal thrombus.

Augmentation can sometimes be used in difficult cases (e.g., morbid obesity or edema) to distinguish vasculature. This maneuver requires the application of color Doppler to the vein being visualized, then squeezing the leg at any area distal to the placement of the probe. Augmentation results in a rush of increased venous flow at the level of the probe. Theoretically, greater flow in the vessel rules out thrombus between the level of the vessel being visualized and where the leg is squeezed. However, augmentation does not provide additional meaningful information to the compression study [21] and 17–35 % of patients with DVT still show augmentation [22, 23]. For these reasons, augmentation is not a required part of the LE evaluation and should only be reserved for use when standard LE ultrasonography is inconclusive.

Starting in the supine position, identify the IJ in the transverse plane, sitting adjacent to the carotid artery. Evaluate the lumen of the IJ for visible thrombus, and perform compression. Typically, the IJ can be traced starting at the mastoid and progressing distally to its entry into the brachiocephalic vein. Since compression of the brachiocephalic is not possible because of the overlying clavicle, place color Doppler over the vein and watch for luminal filling from wall to wall. Pulse wave Doppler is then applied to look for presence of flow. Absence or reduction in flow is considered positive for the presence of a DVT. The subclavian vein is then found and traced toward the shoulder above the clavicle, but similar to the brachiocephalic vein, it is not compressible. Doppler interrogation with both pulse wave and color should be used throughout the course of the subclavian vein. Not only will pulse wave Doppler help to identify an area of the vein with clot, it will help to distinguish artery from vein in a confusing and difficult region. Small pulsations will be seen when pulse wave Doppler is applied to the vein, but these pulsations are generally less pronounced than in the artery. Further assisting in differentiation between artery and vein is the demonstration of respiratory variation with venous pulsations. Nearing the shoulder, the proximal portion of the axillary vein will also be obscured by the clavicle, therefore necessitating the continued use of Doppler interrogation of the vessel. Consider elevating and extending the arm outward to help engorge the veins if the distal subclavian and axillary veins are not visualized [29]. Once in the axilla, the brachial vein is compressible as it runs distally toward the antecubital fossa before splitting into the radial and ulnar veins. Throughout the UE examination, visible clot, a non-compressible segment, or lack of Doppler flow is diagnostic for a DVT.

A 2–4-MHz phased-array transducer is used to find four standard echocardiography windows: parasternal long axis, parasternal short axis, apical four-chamber, and subcostal long axis. Though all four windows should always be obtained, the most helpful windows are the parasternal short axis and the apical four-chamber. A good parasternal short view is generally created after successfully obtaining a clear parasternal long picture. The transducer is placed just to the left of the sternum in the 3rd–4th intercostal space, with the indicator facing toward the patient’s right shoulder. Once a clear parasternal long view is obtained showing the RV, LV, mitral valve, aortic outflow tract, and aortic valve (Fig. 13.9), the probe is then rotated 90° clockwise in the same position to produce the parasternal short axis view. This view provides a clear picture of the LV (typically round in appearance) with the RV seen to the top left of the image screen (Fig. 13.10). The transducer should be adjusted until the papillary muscles are clearly seen in the LV. The presence of RV strain is demonstrated by a dilated RV as it wraps around the LV. In cases where a PE is causing obstructive shock secondary to RV pressure overload, the septum between the RV and LV will be pushed into the LV lumen. The LV will then lose its round appearance and adapt a flattened shape, commonly referred to as a “D-shaped septum” (Fig. 13.11). The apical four-chamber view is obtained by sliding the probe laterally to the apex of the LV, at the point of maximum impulse, with the indicator facing the patient’s left side. This view shows the RA, RV, left atrium, and LV with the corresponding valves (Fig. 13.12). Knowing that the RV is normally approximately 60 % of the size of the LV, evidence of a large, dilated RV or an interventricular septum that pushes into the LV suggests hemodynamically significant PE in undifferentiated shock. This view also allows for evaluation of McConnell sign (normal apical movement with decreased RV free wall contractility) and for presence of abnormal echogenic densities within the RA or RV signifying the presence of clot. Absence of all of these findings makes PE an unlikely cause of shock.