Abdominal paracentesis

An abdominal paracentesis (plural: paracenteses),more commonly referred to as an ascitic tap, is a procedure that can be performed to collect peritoneal fluid for analysis or as a therapeutic intervention.

Indications

• diagnostic: especially for newly-diagnosed ascites
  • determine aetiology of ascites
  • assess for bacterial peritonitis
• therapeutic
  • to relieve pressure effects of ascites, including respiratory compromise

Contraindications

• absolute
  • surgical abdomen
• relative ⁴
  • coagulopathy (INR >2.0)
  • severe thrombocytopenia (platelet count <50 x 10³/μLμl)
  • abdominal wall cellulitis
  • pregnancy
  • urinary bladder distension
  • intra-abdominal adhesions
  • massive ileus

Procedure

Prior to procedure being performed assessment of the amount and nature of the ascites should be made using preferably CT or ultrasound. The patient's coagulation profile should be considered and informed consent obtained. The indication for the procedure should be considered to determine the volume of fluid to be removed.

Full aseptic technique, with antiseptic skin preparation and infiltration of local anaesthetic should be employed. Patient can be positioned to allow accumulation of fluid to one side.

Procedure can be performed blind using the landmark technique (15 cm lateral to the umbilicus in the right or left lower quadrant) or after ultrasound marking prior to procedure. It can also be done image-guided, almost always with ultrasound ¹.

Ultrasound guidance may be used in either a dynamic or static manner, although both should utilize the same pre-procedural scanning goals; the identification of the largest ascitic collection (3 cm being the minimum safe pocket) and where the abdominal wall is free of vessels or excessive adipose tissue.

• static technique ⁵
  • the ideal entry site is marked with two perpendicular lines indicating the location of the targeted fluid pocket, as identified in two orthogonal planes
  • the catheter-over-needle apparatus is inserted in a perpendicular manner at the junction of the aforementioned markings
• dynamic technique
  • either short axis or long axis visualization may be used
    •  the latter allows visualization of the needle throughout the procedure
    • the former relies on intermittent visualization of the needle tip
    • either approach necessitates a 45 degree angle of entry, either at the mid-point of the probe footprint (short axis) and advancing the needle in an out-of-plane manner, or slightly lateral to the probe footprint (long-axis), advancing in an in-plane manner.

An 18G needle with a 10 mL syringe is passed using a Z-track technique, to minimise the risk of persistent leak following removal. Negative pressure is kept on the syringe until ascitic fluid is aspirated, with subsequent catheter advancement, needle removal, and attachment of a three way stopcock.

The Seldinger technique can be used to leave an ~8 Fr catheter in situfor therapeutic procedures. Alternatively a trocar catheter set can also be used. 

Fluid can be sent for the following tests:

• Gram stain, culture and sensitivity
• cell count (especially neutrophils)
• cytology
• albumin levels (to assess serum ascites albumin gradient (SA-AG)
• triglyceride level (high in chylous ascites)
• glucose level
• lactate dehydrogenase level
• amylase level (suggests pancreatic pathology)
• pH

PostprocedurePost Procedure's care should be taken with therapeutic procedures to avoid large fluid shifts. Albumin needs to be replaced parenterally to avoid disequilibrium, in recognition of the risk of post paracentesis circulatory collapse, most commonly indicated when >5 liters of fluid is vacated. Diuretics, salt and water restriction are frequently used.

Complications

• persistent leak (can be collected in stoma bag until heals, minimised with Z-track technique) ¹
• circulatory collapse (minimised by replacing volume and albumin) ²
• bleeding (locally or intraperitoneal) due to low platelet counts, elevated INR and low serum fibrinogen levels ⁶
• localised infection
• bowel perforation
• the hepatorenal syndrome