How to Perform Abdominocentesis

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 Diagnostic Abdominocentesis 

Diagnostic abdominocentesis (obtaining a sample of the abdominal fluid for testing) is quickly and easily accomplished using ultrasound-guidance, a 22 Ga needle (1.5" for large / medium dogs; 1" for small dogs and cats).
The goal is to obtain enough sample to test the fluid. While ultrasound guidance is preferred, it is not necessary. The standards sites for blind diagnostic abdominocentesis are the paraumbilical sites. Analyze the fluid: Check the PCV/TS of the fluid, to determine whether it is a hemorrhagic or mixed hemorrhagic effusion.
  • This is done by comparing the PCV of the effusion to the peripheral blood; with a purely hemorrhagic effusion, the PCV of the fluid will be GREATER THAN OR EQUAL TO  that of the peripheral blood.
If the fluid is not purely hemorrhagic, it is worthwhile to run additional tests:
  •  Glucose/lactate measurement for septic peritonitis:
    • There is a quick, inexpensive and highly sensitive technique for quickly identifying septic peritonitis. You can compare the lactate and glucose levels of abdominal effusion vs. peripheral blood to identify septic peritonitis. In septic peritonitis:

      -The lactate of the abdominal fluid will be greater than 2 mmol/L HIGHER than the lactate of the peripheral blood. The sensitivity and specificity of this finding for diagnosing septic peritonitis has been reported at 100%.

      You can also compare the glucose levels.

      -The glucose of the abdominal fluid will be more than 1.11 (20 mg/dl mmol/L) lower than the blood glucose of the peripheral blood. Using a cut-off of 38 mg/dl (2.1 mmol/L) improves the specificity of this test.

    • ***If the glucose/lactate comparison of an effusion confirms that the effusion is septic this initiates a chain of goal-directed interventions for SURVIVING SEPSIS.
  • prepare a cyto-prep of the fluid, and evaluate this under the microscope to rule out septic peritonitis. To prepare a cyto-prep, spin sample of the effusion, draw off the supernatant, and prepare the white buffy coat onto a slide. You can also do this using standard hematocrit tubes, and using a needle to extract the buffy coat (this is usually where bacteria, white blood cells, and other type of cancer cells will be located.)
    • Identifying intracellular bacteria on cytology of an effusion confirms that the effusion is septic and initiates a chain of goal-directed interventions for SURVIVING SEPSIS. Surgical intervention is often needed.
  • Measure the creatinine and potassium of the abdominal fluid (and compare this to the peripheral blood values) to rule out uroabdomen.

Abdominal Catheter Placement and Therapeutic Abdominocentesis

Abdominal Catheter placement and therapeutic abdominocentesis: Step by Step
Prepare your supplies: Start by getting all of your supplies out and ready to go. Remember to label any syringes containing drugs and medications.
-Clippers and surgical scrub
-Lidocaine for local anesthetic usually 1-2 mL depending on patient size; I prefer a 25 ga needle to minimize discomfort
-A marker or sharpie
-Sterile gloves (for you) and regular/nitrile gloves (for your assistant) Some people do this without sterile gloves. Personally, I don’t.
- 20-20 Ga hypodermic needle attached to a regular IV extension set (~30 cm) or -23-21 Ga Buttery fly catheter I prefer this setup for medium to large dogs     And this setup for small dogs and cats
-A three-way stopcock or one-way valve
-60- ml syringe (or smaller if the patient is tiny)
-Sample tubes labeled “effusion” for fluid analysis/cytology (lavender/ EDTA tube) and culture.
-Bowl or other container for collecting the effusion *If the effusion looks hemorrhagic, collect it aseptically into 60 cc syringes and keep close by in case you need it for autotransfusion.


Attach the extension set to the three-way stopcock and syringe, and ensure that all of the connections are very secure. Make sure that your assistant knows how to operate the three-way stopcock.

Select Site, Clip Fur, and Infuse Local Anesthetic:
Start by selecting your optimal centesis site using ultrasound. This is usually within a few centimeters of the umbilicus. Clip the selected side generously. I like to circle my optimal centesis site (identified by ultrasound) with a sharpie, and then infiltrate local anesthetic into that area, making sure that I go deep enough into the intercostal musculature and to minimize discomfort as I pass the catheter through the chest wall.
Scrub Site and Fenestrate Catheter:
Your assistant can then aseptically scrub the site while you put your sterile gloves on and begin to “fenestrate” the catheter. If your black circle starts to disappear, have your assistant re-mark it before a final scrub. Fenestrate the catheter ((fenestra means window in Latin). You will only fenestrate the distal ¼ to 1/3 of the catheter. When you fenestrate the catheter, leave the stylet in the catheter and make small apertures or windows in the catheter so that there will be less resistance to flow. Make sure that your holes are evenly spaced and small, and that you are not leaving any burs in the catheter or compromising its integrity. You would not want any pieces of the catheter to break off inside of the patient.
Introducing The Catheter:

It is generally preferred to perform abdominal catheter placement and therapeutic abdominocentesis with the patient in lateral or dorsal recumbency. At the selected site, make a small (1-2mm) stab incision into the skin using your scalpel blade, so that there will be less drag on the catheter as you pass it through the skin and abdominal wall. Grab your catheter, and remember that this is just like a gigantic IV catheter. If you look at the tip, you will notice that the metal style protrudes a couple of millimeters beyond where the actual Teflon catheter starts. You can begin to slowly advance the catheter and stylet together through the skin. Twisting the catheter slightly between your fingers can help reduce resistance. As the catheter stylet reaches the target pool of fluid, you will see a flash in the hub of your catheter. At this point, you will advance your stylet and catheter together a couple more millimeters, and then, holding the stylet still, feed the catheter off the stylet (while holding the stylet still), the same way you would if you were feeding a catheter into a vein. It may help to twist/rotate the catheter between your fingers as you slide it off the stylet. Remove the stylet, and temporarily occlude the hub of the catheter while you attach the extension set. Your assistant can begin to aspirate the fluid by drawing back on the syringe.

Prepare your samples for fluid analysis, and then continue draining the effusion. When you are done, remove the catheter and place a biocclusive over the site.

For the next 1-2 hours (then less frequently), continue to monitor the site intermittently with ultrasound for recurrence of pericardial effusion, and continue to monitor the patient’s vital parameters (heart rate, blood pressure, EKG) continuously if possible. 

If you are draining an effusion, prepare your samples for fluid analysis, and then continue draining the effusion. Quantify the volume you retrieved and record it in the patient’s chart. When you are done, remove the needle. Continue to monitor the patient for dyspnea (as well as other changes in vital parameters), and check the site intermittently with ultrasound for recurrence.

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