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You can augment venous flow by squeezing the leg distal to where you are scanning. If Color Doppler demonstrates a homogenous increase in venous flow, this suggests that there is no occlusive thrombus between where you are squeezing and scanning. However, if there is no increase in venous flow, there could be a DVT.
Editor’s Note: Use this method with caution as there could be a risk of dislodging any existing clots and causing a pulmonary embolism.
You can also detect a DVT by compressing the veins. If you apply pressure with the probe until the artery compresses slightly and the vein compresses completely, there is likely no DVT at that spot. However, if you apply enough pressure that the artery compresses but the vein does not compress completely this is considered a “non-compressible” vein and it is likely the patient has a clot in that region.
Depending on the age of a clot, you may see an echogenic mass inside the vessel on ultrasound if your probe is directly over the mass. You may not be able to see acute thrombi because they are anechoic or hypoechoic and they tend to be near the edges of the lumen. As the thrombus ages, it becomes more echogenic and retracts from the vein walls, making it much easier to detect with ultrasound. Therefore, when scanning for clots, do not just rely on direct visualization and always be sure to perform the compression technique to not miss any acute DVTs.
Examples of Direct Clot Visualization of DVT
Deep vein thrombosis can be detected in three ways using point of care ultrasound: direct clot visualization, non-compressibility of vein, and augmentation with Color Doppler.
Direct visualization of the echogenic clot with ultrasound is a definitive way to detect a DVT. Among the indirect ways for diagnosing a DVT, compression ultrasound provides the highest sensitivity and specificity. A study of 220 symptomatic patients scanned for DVT with compression ultrasound yielded a 100% sensitivity and 99% specificity (Lensing et al, 1989). In comparison, augmentation with Color Doppler does not improve the accuracy of scanning and requires squeezing the patient’s leg, which could dislodge any present clots and cause a pulmonary embolism (Lockhart, Sheldon & Robbin; Blaivas et al).
Our recommendation to diagnose DVT is to first use the direct visualization technique. If an echogenic mass is not apparent, we recommend evaluating the compressibility of the veins. The use of color Doppler and augmentation are optional modalities.
Remember to download the DVT Ultrasound Pocket Card PDF as a reference for DVT Ultrasound technique, pathology, and false positives:
