Our protocol describes a simplified yet validated approach to diagnostic point-of-care ultrasound by describing a three-zone protocol for lower extremity DVT image acquisition. Providers appropriately trained in focused point-of-care ultrasound can perform a rapid bedside DVT examination with high sensitivity and specificity in critically ill patients. Diagnostic POCUS exams can expedite the diagnosis of DVT and thereby initiate earlier treatment with potentially decreased complication rates and improved patient clinical outcomes.
Key steps for appropriate DVT image acquisition include proper patient positioning, adequate gain and depth, and complete compression of the veins'vessel walls to ensure no thrombus is present. Select the high frequency linear transducer for the deep venous thrombosis or DVT scan to ensure a high resolution image of the veins. Next, set the depth, gain, and focus.
Set the depth so that the target vessels appear in the middle one-third of the ultrasound screen by pressing the up or down depth button. Then set the gain so that the vessels contain a few spots of gray but are otherwise black by pressing the right or left gain button and turning the dial. If the machine has the capability, aim the focus beam at or slightly below the level of the target vessels by clicking the box on the screen and moving it while holding down the button and then release.
Set the machine mode. Click on B-mode, which is a two-dimensional gray scale ultrasound exam, to obtain both the non-compressed and compressed images. For optimal scanning ergonomics, place the machine with the ultrasound in a direct line of sight with the ultrasound probe.
Before scanning, expose the patient's entire leg from the groin to the knee. Place the patient supine for DVT examination of the common femoral and femoral veins. Place the patient in the frog-leg position to enable better visualization and scanning of the distal veins.
For B-mode scanning of the groin and thigh, apply gel to the patient's skin in a linear path that traces out the expected path of the ultrasound transducer to increase the efficiency of motion. For B-mode scanning of the knee, apply gel to the transducer itself, as a generous gel application will facilitate the scanning efficiency. Next, for transducer orientation, place the transducer in a transverse position with the orientation marker directed toward the patient's right side to ensure that images captured during scanning correspond to the anatomical direction of the structures.
Place the probe perpendicular to the path of the vein to visualize the vein in a short axis view. Center the venous structure on the screen. Add long axis imaging in ambiguous cases by rotating the probe 90 degrees so the marker points towards the patient's head.
For compression sequence, begin scanning immediately coddle to the inguinal crease. Progress distally sequentially with downward compression and then release at each point. Compress such that the entire vein collapses with the anterior wall touching the posterior wall while the artery remains pulsatile.
Do not apply resting surface pressure between each compression, as it can obscure the visualization of the veins. The vein should collapse fully when enough pressure is applied with the transducer to indent an adjacent artery. Click save clip and compress.
Then release the common femoral vein or CFV and femoral artery or FA just below the inguinal ligament. Slide the probe distally about one centimeter and record the same compression and release technique at the CFV and FA at the intake of the great saphenous vein or GSV. Click save clip, then compress and release the probe at the CFV at the bifurcation of the FA into the superficial femoral artery or SFA and deep femoral artery or DFA.
Between the SFA and DFA, there will be a lateral perforator vein draining from the lateral to medial into the CFV. Ensure that both the lateral perforator vein and GSV are compressible. Click save clip, then compress and release the probe at the CFV at the bifurcation of the CFV into the femoral vein or FV and deep femoral vein or DFV.
Again, click save clip, compress, and release the probe at the popliteal vein behind the knee. Once points one to five are fully compressible, scan the FV along the thigh from proximal to distal until the vein disappears into the adductor canal. During this scanning process, attempt to compress the vein approximately every one to two centimeters.
In this study, left leg vascular anatomy with negative and positive lower extremity DVT examples in transverse views, are shown here. In a negative DVT study, the veins are completely collapsible with the interior wall touching the posterior wall during compression ultrasound in all the zones. In a positive DVT study, proximal vein POCUS can both directly visualize a thrombus or detect non-compressibility of the proximal veins, which is diagnostic of a non-occlusive thrombus.
The protocol explains the steps in obtaining DVT images at six compression points in the lower extremity from the proximal thigh, moving distally, to the popliteal space.
