The Compression Ultrasound Technique

The Principle of Coaptation

To accurately detect a Deep Vein Thrombosis, we rely on the physical property of healthy veins: their ability to collapse under pressure. This is known as coaptation. In a normal study, the anterior and posterior walls must touch, completely obliterating the lumen. If a clot is present, the vein will remain visible or only partially compress, regardless of the force applied.

The Plane of Truth: Transverse vs. Longitudinal

Compressions must always be performed in the transverse, or short-axis, plane. Why? In a longitudinal plane, the probe can easily slide off the side of the vessel. This 'rolling' effect can trick you into thinking the vein has compressed when it has simply moved out of view. By staying transverse, you can use the adjacent artery as a landmark to ensure your pressure is direct and centered.

Terminology Matters: FV vs. SFV

Standardized terminology is a matter of patient safety. The Society for Vascular Ultrasound strongly discourages the term 'Superficial Femoral Vein.' Non-imaging clinicians often hear the word 'superficial' and assume a clot there is low-risk. To prevent this potentially fatal misunderstanding, always refer to this deep vessel simply as the Femoral Vein.

Recap: Compression Fundamentals

Let's review the fundamental principles of the compression technique before we move on to the practical protocol.

The Standardized Compression Protocol

To begin, place the patient in a reverse Trendelenburg position. This increases venous pressure, distending the veins for better visualization. Using a high-frequency linear probe in a transverse orientation, perform compressions every 1 to 2 centimeters. Pay special attention to the Saphenofemoral Junction and the femoral confluences, as these are high-risk areas for thrombus.

The 'Stiff' Vessel Challenge

You encounter a 'stiff' vessel. The femoral vein won't collapse, but the adjacent artery is heavily calcified. How would you adjust your technique to determine if this is a true DVT or a false positive? Type your plan below.

Technical Pitfalls & Anatomical Hurdles

Even with perfect technique, anatomy can be challenging. In the adductor canal, the vein dives deep, often requiring you to push from the back of the leg. In the groin, enlarged lymph nodes can mimic a non-compressible vein. Finally, remember that obesity and edema can absorb your probe pressure, leading to false-positive results if you don't press firmly enough.

Recap: Protocol & Pitfalls

Before the final assessment, review these standardized protocol steps and the common anatomical challenges that can mimic a clot.