Seeing Through the Clot: A Guide to DVT Ultrasound Anatomy

When it comes to diagnosing a DVT (deep vein thrombosis), a potentially life threatening clot one cannot afford to miss the DVT on ultrasound.

It can eventually lead to pulmonary embolism and hemodynamic instability etc. And anatomy textbooks filled with complex diagrams and dense terminologies can be overwhelming to understand. They might often leave you wondering how it applies to the real world.

Well, this guide is aimed to bridge the gap and translate DVT ultrasound anatomy into clear and actionable steps.

Preparing the patient for DVT Ultrasound

1. 1. Get the patient lying down in supine (on back) position. Raise the head of the bed to 30°. This helps increase blood to veins of the lower extremities and veins will pop out for clearer views.
   2. Frog leg flex: Gently guide the patient's leg into frog leg position, externally rotated and knee slightly bent. This is ultrasound gold: bigger veins, easier access from common femoral to popliteal. No repositioning needed.

Preparing the ultrasound probe

• Use linear ultrasound probe.
• Place the ultrasound machine on the patient's right side. This let you scan smoothly with your right hand while making the adjustment on the machine with your left hand.
  
  

DVT Ultrasound Anatomy

For an ultrasound to check for blood clots (DVT) in the legs, we need to know about these main veins:

1. Common Femoral Vein (CFV): This is a big vein near the top of the thigh.
2. Great Saphenous Vein: This vein branches off the CFV and runs closer to the skin's surface.
3. Deep Femoral Vein and Femoral Vein: Deeper inside your thigh, the CFV splits into these two veins.
4. Popliteal Vein: All the veins mentioned so far come together behind the knee in this vein.
5. Trifurcation Veins: The Popliteal Vein splits into three smaller veins in your lower leg:
   • Anterior Tibial Vein (front)
   • Posterior Tibial Vein (back)
   • Peroneal Vein (side)

That's all you need to remember for the ultrasound! These are the important channels we check for blockages caused by blood clots.

Important note: Femoral Vein was earlier known as Superficial Femoral Vein. Hence don’t get confused with the name.

How to Compress the Vein for Ultrasound?

Squeeze the vein until the pulsing artery beside it flattens a tiny bit. If the vein squishes completely shut, there's likely no clot.

• Why You Squeeze: This helps us spot blood clots. If a vein doesn't close completely when squeezed, there is a chance it’s blocked by a clot.
• Tricky Part: It's important to apply the pressure at the right amount. Too little pressure and a healthy vein might look clogged. Too much and the results might be misleading.
• Practice Makes Perfect: Learning the right amount of squeeze takes practice, but it's an important skill for accurate DVT diagnosis.
  
  

DVT Ultrasound Procedure

Step 1: Scan the Femoral Vein

1. Setup
   • Gel Up: Put gel on the ultrasound probe for smooth movement and clearer images.
   • Finding the Landmark: Place the probe on the inguinal ligament (the crease near the top of the thigh), halfway between two bony points (pubic symphysis and ASIS).
   • Probe Position: Hold the probe straight up and down (perpendicular). The indicator (probably a little dot or notch) should face the patient's right side.

2. Finding the Vessels
   • The CFV and CFA: You're looking for the common femoral vein (CFV) and common femoral artery (CFA). The vein (CFV) will be closer to the inside of the leg than the artery (CFA).

3. The Key Step - Compression
   • Press and Check: Apply firm pressure with the probe until the artery flattens slightly. THIS IS IMPORTANT for checking for clots.
   • Normal vs. Clot: A normal vein will completely disappear (collapse) under this pressure. If it doesn't, that's a sign of a potential DVT.
     
     

Step 2: Scan the Great Saphenous Vein

1. Move the Probe
   • Slide the probe a tiny bit down the leg (maybe an inch or two).
   • You're searching for the spot where a big surface vein (Great Saphenous Vein) branches off the main vein (CFV).
   • Keep the main vein and artery centred on the screen as you move the probe.

2. Watching the Split
   • As you move down, you'll usually see the artery split into two first, and then the main vein will split.

3. Squish and Check
   • Put the probe where the big surface vein (Great Saphenous) splits off from the main vein (CFV).
   • Press down firmly with the probe to squish that main vein.
   • Remember: A healthy vein will squish completely shut. If it stays open, there might be a clot.

Important Note: Even if a clot is only in the big surface vein, it can be serious and needs treatment just like a clot in the main vein.

Step 3: Scan the (Superficial) Femoral Vein

1. Move the Probe and Find the Split
   • Slide the probe a tiny bit down the leg.
   • Look for where the main vein (CFV) splits into two:
     • One vein goes deep into the leg (deep femoral vein)
     • One vein stays closer to the surface ((superficial) femoral vein)

2. Follow the Surface Vein
   • This surface vein ((superficial) femoral vein) stays right next to the artery. Keep your focus on these two as you move the probe.

3. Squish and Check (Right After the Split)
   • Put the probe where the main vein splits.
   • Press the probe to gently squish the surface vein ((superficial) femoral vein).
   • Remember: A healthy vein squishes flat, but a clot keeps it open.
     
     

Optional: Check Further Down

• You can slowly move the probe down the leg, keeping the surface vein and artery in view.
• Every so often, squish the surface vein. This helps find clots if they're further down the leg.
  
  

Step 4: Scan the Popliteal Vein

1. Move the Probe to the Back of the Knee
   • Find the crease behind the patient's knee.
   • Put the probe right in the middle of that crease.
   • Scan a little bit up and down from this spot to find the popliteal vein.

Tip: If you can't find the vein, try putting the probe directly between the two big tendons (hamstring tendons) behind the knee. The vein is usually close by!

2. Squish and Check
   • Once you see the popliteal vein, use the probe to gently press and squish it.
   • Remember: A healthy vein squishes flat, but it stays open if there's a clot.
     
     

Important note: Things are flipped!

• At the back of the knee, the positions are switched. The vein (popliteal vein) is now on top, and the artery (popliteal artery) is below it on the screen.
• A helpful reminder: "Pop on Top!"
  
  

Step 5: Scan the Trifurcation of the Popliteal Vein

1. A Little Further Down
   • Keep the probe behind the knee, but slide it down the leg just a bit.
   • You're searching for where the main vein (popliteal vein) splits into three smaller ones.
2. Squish and Check (As You Go)
   • As you move the probe down, gently squish the main vein (popliteal) every so often.
   • Remember: It should squish flat if it's healthy. A clot keeps it open.
3. Finding the Split = You're Done!
   • Once you see the main vein split into three smaller ones (anterior tibial, peroneal, and posterior tibial veins), you've reached the end of the DVT ultrasound exam.