Ultrasound
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Image 1 does indeed show ascites. The ascites appears anechoic (black) and is in the nearfield (top of the image) as opposed to the intestine, which appears hyperechoic (white) and is in the farfield (bottom of the image). In real time, you can also often see the bowel moving within the ascitic fluid during peristalsis. You may even see the bowel contents moving within the bowel walls. It’s hard to estimate the total amount of ascitic fluid in the abdomen with just one view, but you could estimate how much you see in just the image above by using the centimeter markers at the bottom and left side of the screen. The pocket appears to be between 5-7cm deep and at least 14cm across. A second view with the probe rotated 90° (not shown) noted a maximal depth of 10cm. If the pocket were a rectangle that was 6 X 14 X 10 cm, then the total volume of just this part of the pocket would be about 840ml. This pocket looks like a quite promising location to do your tap, but it always makes sense to compare sides before making your final choice.

Factors other than pocket size are important to consider as well. For example, you want to avoid puncturing an enlarged liver or spleen. Find adjacent organs while you are performing your scan. You also would want to avoid any surgical scars, because adhesions in the area may tether down bowel and increase the risk that you will perforate them with your needle. Proper positioning for paracentesis is also important. Since bowel floats, it is recommended that the patient be positioned with the head of the bed elevated between 45 and 60 degrees. The bowel will rise and the fluid will collect in the lower abdomen. Repositioning the patient after the ultrasound, but before the tap however, is ill advised. Any repositioning may cause the bowel and fluid to shift and increases the risk of hitting bowel. The one botched tap I have done was due to repositioning a patient. He had a belly full of fluid by an ultrasound that was done in the supine position. I then sat him up to do the tap and could not get any fluid at all. I ended up aspirating peritoneal gas. When I ultrasounded him again, all the fluid had mysteriously disappeared. As it turned out, the patient’s “ascitic fluid” was actually all urine due to a ruptured bladder, and when I had repositioned him, it had all siphoned off into the Foley catheter that the nurse had placed. This scenario is rare, but it reinforces the importance of doing the ultrasound right before you do the tap, with no repositioning in between.

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Image 2 shows the same pocket magnified after the paracentesis catheter has been inserted. The catheter appears as a linear, hyperechoic structure. In all, 6 liters were safely drained off this particular patient, and he went upstairs quite pleased about his rapid weight loss, joking that he should be a contestant on “The Biggest Loser”.

 

 

 

 

PARACENTESIS: (Safest with real time US guidance)

Indications
-Diagnostic: new ascites, r/o infected ascites
-Therapeutic: tense ascites, respiratory distress
Contraindications:    
-Uncooperative patient, scar or cellulitis at site, bowel
obstruction, pregnant, DIC, tPA in use
Relative: INR >1.5-5.0
-Most experts say tap is OK regardless of INR.
-Platelets < 50. Attempts to correct INR may cause more complications than the procedure itself.
Preparation:    
-Decompress bladder, position HOB at 45-60° (bowel floats) then use US to find best pocket
Ultrasound Technique:   
-Use curved probe. Find and measure biggest fluid pocket (usually RLQ or LLQ) with no vessels or organs in way.
-Don’t reposition patient after ultrasound, as fluid may move. Avoid scars, veins & big spleen
-Use Z-puncture. Pull skin down 2 cm before inserting needle to prevent leakage from site afterwards
Diagnosis:
-SBP: > 250 PMNs, >1000 WBC, Serum-Ascitic Albumin Gradient < 1.1
-Exudative: Protein >3 or ratio >0.5. LDH >200 or ratio >0.6, specific gravity >1.016
 
 
Click next for Pearls & Pitfalls for Ultrasound-Guided Paracentesis

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