Slide 1: Approach to paracentesis.

Why use POCUS for paracentesis? Paracentesis is generally a very safe procedure – however, the use of ultrasound is recommended to reduce the risk of bleeding, and to increase the likelihood of finding a large fluid pocket.

The evidence. Studies have found that ultrasound-guided paracentesis is more likely to be successful and is less likely to cause complications. A study of EM residents found that ultrasound-guided paracentesis had a higher success rate (95% versus 61%, P = 0.0003) compared with landmark guided procedures. Ultrasound-guided paracentesis had a lower rate of adverse events (such as infection, hematoma, and seroma) compared with landmark technique (1.4% versus 4.7%, P = 0.01).

Ultrasound can be used in two ways to guide paracentesis. Static: a non-sterile ultrasound probe is used to mark a fluid pocket and epigastric vessels prior to performing the sterile procedure. Dynamic: an ultrasound probe is placed in a sterile sleeve and used in real time to guide the sterile procedure. This is an advanced technique recommended for skilled users trying to sample smaller pockets.

Let’s explore two POCUS micro-skills to perform paracentesis more safely and with higher diagnostic yield.

Micro-skill one. Marking epigastric vessels. Step 1. To mark the epigastric vessels, place the linear probe just lateral to the umbilicus in the trans-umbilical plane. Step 2. Set the depth so that you can see the abdominal wall and the ascites below. Step 3. Slowly move the probe laterally until you visualize the epigastric vessels. They are small dark circles deep to the muscle/fascia. Step 4. You can use color doppler to confirm flow if you are uncertain. Step 5. Once you’ve found the vessels mark the skin with a marking pen. Step 6. Slide the probe vertically to follow the course of the vessel and mark the vessel course.

Consider safety! In patients with cirrhosis, the epigastric vessels can become distended. Injury to the epigastric vessels from paracentesis can cause life threatening bleeding. Note: bowel moves dynamically, so it is prudent to perform the procedure immediately after marking the skin.

Graphic showing the epigastric vessels with arrows pointing to the superior epigastric artery and vein, and the inferior epigastric artery and vein. The epigastric vessels run vertically along the anterior abdominal wall. The exact location varies from person to person.

Micro-skill two. Finding a fluid pocket. The ideal fluid pocket is large (greater than 5 centimeters) and far from loops of bowel or spleen/liver. Step 1. Use the phased array probe to scan the abdomen and examine all four quadrants. Step 2. Measure the depth of the fluid pocket with distance calipers. Be careful not to exceed this depth when performing the procedure! Step 3. Rotate 90 degrees and measure again in an orthogonal plane. Step 4. Mark the skin with an X.

Ultrasound images showing safe versus risky fluid pocket. Safe is a large pocket far from any organs. Risky is a small pocket close to the liver.