Pos neg pos neg pre test probability for dvt d dimer

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pos neg pos neg Pre-test probability for DVT D-dimer D-dimer Low Moderate/high Safe not to anticoagulate Negative DVT US in ED, repeat at 7days Consider formal study, anticoagulation Figure 8.17 Clinical protocol for the evaluation of possible DVT. V Figure 8.16 This longitudinal image of the common femoral vein (V) demonstrates echogenic material within the lumen. Note that the thrombus does not occlude the entire vessel diameter. This could represent a chronic DVT, where some recannulation has begun to take place. Diagnostic ultrasound 185 Ultrasound of the deep venous system
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Advanced techniques Upper extremity DVT involving the internal jugular, subclavian, or axillary veins can impact patients who are hypercoagulable or have indwelling cen- tral venous or percutaneous inserted central catheters (PICC). The test char- acteristics of upper extremity DVT assessment using bedside ultrasound have not been described. However, it is reasonable to assume that clot would cause a lack of vessel compressibility just as with lower extremity DVT. Therefore upper extremity assessment may be more useful in confirming the presence of DVT than excluding the diagnosis. In addition, using compression to assess for vessel patency is recommended prior to attempts at central venous cannulation (see Chapter 15 ). Figure 8.18 demonstrates thrombus within the internal jugular vein. Undiagnosed, this process could make internal jugular vein cannulation dangerous and likely impossible. Although not frequently employed by emergency physicians, assessing augmentation and respiratory variation using pulsed-wave Doppler is a common practice among radiologists. In cases where a stronger clinical suspicion for DVT may lead one to pursue a more involved bedside study, the following techniques may be employed. Both techniques involve the use of Doppler to visualize flow differences in the veins. Augmentation To assess augmented venous return, compress the soft tissue of the calf at some point distal to the standard probe position on the leg. With the Doppler over the vein, note any changes in flow as the distal vein is compressed. In a normal vein, distal compression causes a rapid, temporary increase in venous return. This implies an unobstructed path for blood flow distal to the probe, Figure 8.18 Thrombus (*) within internal jugular vein (V). With pressure ( right ), neither the vein nor the carotid artery (A) compress. 186 Diagnostic ultrasound Ultrasound of the deep venous system
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from the point of compression. In Figure 8.19 , note the rapid increase in flow velocity on the scale at the bottom of the screen. The arrow indicates the augmentation. Respiratory variation To assess respiratory variation, note any changes in flow during respiration with the Doppler over the vein. In a normal vein, changes in intra-abdominal and intrathoracic pressures during the respiratory cycle cause cyclic vari- ations in venous return. This implies an unobstructed path for blood flow proximal to the probe, toward the iliac veins and inferior vena cava.
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