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Diagnostic abdominal paracentesis (ascitic tap) [advanced]

Please note content is for educational purposes only and procedures should not conducted based on this information. OSCEstop and authors take no responsibility for errors or for the use of any content.

Indications: diagnosis of cause of new ascites; diagnose spontaneous bacterial peritonitis or other infections (e.g. abdominal TB); diagnose blood in peritoneal space in trauma

Relative contraindications: severe coagulopathy (disseminated intravascular coagulation or accelerated fibrinolysis); pregnancy; distended bowel (obstruction/ileus); organomegaly; distended bladder


  • Wash hands, Introduce self, Patients name & DOB & wrist band, Explain procedure and get written consent
    • Risks: pain; bleeding; infection; damage to local structures (including bowel perforation); paracentesis leak
    • Ask patient to empty their bladder prior to procedure
  • **Check patients clotting screen, platelet count and if they have been on an therapeutic anticoagulant/clopidogrel**
  • Ensure assistant is available
  • Examine patient and tap out ascites
  • Use ultrasound to confirm the presence/location of ascites, check the depth of the abdominal wall and mark the spot pre-procedure (although, if there is tense ascites with fluid thrill, it is usually safe to proceed without ultrasound)

Preparation part

  • Wash hands and apply apron
  • Clean a trolley
  • Gather equipment onto bottom of trolley (think through what you need in order)

Equipment list

  • Sterile pack
  • Cleansing snap-sponge x2 (iodine or alcohol/chlorhexidine)
  • OPTIONAL: Sterile drape with hole in centre (or 2-3 drapes without holes in)
  • 10ml syringe and 3 needles (1 blunt fill 18G drawing-up needle, 1 orange 25G, 1 green 21G) for local anaesthetic
  • 20ml syringe and green 21G needle for aspirating ascitic fluid
  • Cotton gauze swabs (used whenever needed throughout procedure to dry/clean sterile area)
  • Sterile dressing
  • Equipment to be kept outside of the sterile
    • Sterile gloves
    • 10ml 1% lidocaine (maximum 3mg/kg – note 1ml 1% lidocaine = 10mg)
    • Bottles: 1-3 white-topped sample collection bottles, purple EDTA haematology tube, yellow SST biochemistry tube, blood culture bottles

  • Walk to patient
  • Wash hands
  • Open sterile pack to form a sterile field on the top of the trolley
  • Open packets (without touching the instruments themselves) and drop sterile instruments neatly into the sterile field
  • Pick up waste bag from sterile pack without touching anything else and stick to side of trolley

Patient part

Positioning and exposure

  • Position patient lying supine in bed with head of bed elevated (aids fluid accumulation in lower abdomen)
  • Expose patient’s abdomen

If the insertion point has not already been marked using ultrasound…

  • Locate insertion point:
    • Traditionally in the right iliac fossa (approximately 5cm above and up to 5cm medial to the right ASIS)
    • Tap out ascites and confirm flank dullness at intended insertion point
  • Use different site if there is overlying infection
  • Mark insertion point with a skin pen/indentation


  • Wash hands
  • Apply sterile gloves using sterile technique (open pack on a side surface)
  • Sterilize area
    • Work from middle outwards in one spiral motion (using cleansing snap-sponge)
    • Repeat with second cleansing snap-sponge
    • Discard used snap-sponges as they are no longer sterile, but note all equipment used after this (including all needles) can be returned to the sterile field after use
    • OPTIONAL: Apply the sterile drape over the patient’s body so that the hole is in the correct place to allow access to the insertion site (or apply 2-3 drapes centred around exposed insertion site if no holes)
  • Anaesthetise tract
    • Ask assistant to snap open lidocaine bottle and hold open upside-down
    • Draw up lidocaine using drawing-up needle on 10 ml syringe and expel any air
    • Change to the orange needle and insert at an acute angle to form a single subcutaneous bleb around insertion site in order to anaesthetise the skin
    • Change to the green needle and insert perpendicular to the skin to anaesthetise the insertion tract
      • This is done by instilling lidocaine in small increments of increasing depth
      • Always aspirate when advancing the needle (so you know when you get to the peritoneal cavity) and aspirate before injecting lidocaine (to check you are not in a vessel)
      • When fluid is aspirated, remove needle and do not advance further
    • Wait 1 minute to work


  • Attach new green needle to the 20ml syringe
  • Insert perpendicular to the skin into the same tract, aspirating during infiltration
  • When fluid is aspirated, stop advancing and remove 20ml of ascitic fluid
  • Remove needle


  • Dress wound

To complete

  • Thank patient and cover them
  • Bin waste and gloves, dispose of sharps safely, clean trolley and wash hands
  • Decant ascitic fluid into sample tubes, label them and send to lab
    • MC&S (blood culture bottles or white-top) β†’ microbiology
    • Albumin (white-top or yellow SST tube) β†’ biochemistry
    • Cytology if first ascitic sample (white-top) β†’ histopathology
    • Cell count (purple EDTA top) β†’ haematology
    • Other tests to consider: protein, glucose (paired)
  • Perform venepuncture to determine concurrent albumin level
  • Fully document procedure in patients notes

Learn how to interpret the results too…

Ascitic fluid result interpretation is covered here!

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