Ascites tapping

Synonym: paracentesis

A general discussion of ascites is found elsewhere, including the medical management.

What is ascites tapping?

Ascites tapping is synonymous with paracentesis. It describes a procedure to remove ascitic fluid from the peritoneal cavity.

Paracentesis includes diagnostic paracentesis, where a small volume of ascites is removed for diagnostic purposes only (sometimes referred to as an 'ascitic tap'), and therapeutic paracentesis, where a large volume of ascites is removed for symptom control purposes (also known as large-volume paracentesis or an 'ascitic drain').

Indications

Diagnostic (via either ascitic tap or paracentesis)

Diagnostic paracentesis can be used to determine the aetiology of ascites.

It is particularly useful in ruling out spontaneous bacterial peritonitis (SBP) as a cause of acute deterioration in people with cirrhosis.

The British Society of Gastroenterology recommends performing diagnostic paracentesis:¹

• In all patients with new-onset ascites.

• In all patients with cirrhosis and ascites on hospital admission (urgently - to rule out SBP).

• In patients with ascites and any features suggestive of SBP such as: GI bleeding; shock, fever, or other signs of systemic inflammation; gastrointestinal symptoms; hepatic encephalopathy; or worsening liver or renal function.

• In patients receiving antibiotics for SBP, 48 hours after starting treatment, if the response to antibiotics appears inadequate, or if secondary bacterial peritonitis is suspected.

Therapeutic (usually via paracentesis)

Large volume paracentesis - usually with an ascitic drain - may be used for:¹

• Relief of respiratory distress or abdominal pain resulting from tense ascites, alongside diuretics.

• Drainage of ascites that is refractory to diuretic therapy.

Contra-indications and cautions

Diagnostic paracentesis is generally considered to be a safe procedure, with few contra-indications.² Large-volume paracentesis (therapeutic paracentesis) is more invasive, and requires more caution.³

Absolute contraindications are:^{2 4}

• Disseminated intravascular coagulation or clinically-evident fibrinolysis. (Consider administering platelets or FFP first.)

• An acute abdomen.

• Skin infection at the proposed puncture site. (A different site should be chosen.)

Caution should be taken in the following situations:

• Pregnancy.

• Severe bowel distension (eg, obstruction or ileus).

• Organomegaly.

• Bladder distension.

• Coagulopathy (INR >2) or thrombocytopenia (platelets < 50).

  • Both of these are common in patients with cirrhosis. Diagnostic paracentesis has a very low risk of clinically-significant bleeding, even if these are present.² Platelet or FFP transfusion may be considered if there is particular concern of bleeding risk, including with large volume paracentesis.³

Investigations

Prior to tap

Before tapping there are certain investigations that should be undertaken:

• FBC and clotting screen.

• U&E, creatinine and LFTs.

• Abdominal ultrasound - this is not always necessary prior to tap. It is used to review liver, pancreas, spleen and lymph nodes. Ultrasound is a very sensitive means of assessing the extent of ascites and may also show the causative pathology such as carcinoma of ovary or metastatic liver disease.

Following the tap

After a diagnostic tap the following investigations may be requested.

Microscopy: white cell count, red cell count, Gram stain

• A neutrophil count of >250 cells/mm³is diagnostic of SBP.

• The red blood cell count is usually <1,000 cells/mm³; higher levels raise the suspicion of an underlying malignancy - eg, hepatocellular carcinoma.

• Gram stain of ascitic fluid is usually negative in SBP, where relatively small numbers of organisms are present in ascitic fluid, but may identify secondary bacterial peritonitis from a perforated viscus when multiple organisms are seen.² Samples should also be sent for culture and sensitivity. These should be inoculated into blood culture bottles as soon as the sample is taken. This has almost double the yield of ascitic fluid sent in sterile containers.

Testing for tuberculosis

If tuberculosis is suspected, request acid-fast bacilli staining and culture.

Interferon-gamma release assays (IGRAs), adenosine deaminase (ADA) levels, and PCR diagnostic techniques may also be used to diagnose TB, if available. ⁵

Albumin or protein levels
Traditionally ascites was labelled as an exudate if the protein levels were >25 g/L, or a transudate if protein levels were <25 g/L. This has been superseded by the serum ascites-albumin gradient (SA-AG) which is a better measure.

Amylase
This will be high in pancreatitis-associated ascites.

Triglycerides

Milky-coloured ascitic fluid suggests chylous ascites. If present, triglyceride levels should be measured. Reference ranges vary, but an ascitic triglyceride concentration of 187mg/dL (2.13 mmol/L) has been used as a cut-point above which chylous ascites is likely.⁶

Cytology
The yield is greater with larger-volume samples (>100 ml), especially when concentration techniques are used.

Risks associated with ascites tapping

Paracentesis is a relatively safe procedure. Complications are more likely to occur when other comorbidities are present. Currently the risk of serious complications of paracentesis for cirrhosis is estimated to be about 1 in 100⁷ for minor complications to less than 1 in 1,000 for major events. Risks include:

• Significant bleeding.

• Infection.

• Hypovolaemia and hypotension after large volumes of ascites are removed (over five litres).

  • Human albumin solution should be given when large volumes of ascites are drained, to prevent this.

• Injury or perforation of organs.

• Paracentesis leak.

Precautions

Paracentesis for symptom relief is common, especially if there is tense ascites. Ascites that is refractory to diuretic treatment can be drained with repeated, regular paracentesis; however, individuals with refractory ascites should have their suitability assessed for liver transplantation (the only curative treatment). Transjugular intrahepatic portosystemic stent shunts (TIPSS) are another alternative to repeated paracentesis, in carefully-selected patients.¹

Paracentesis is performed under aseptic conditions, as there is a risk of introduction of infection into the peritoneal cavity. Ascitic drains should be removed within six hours of insertion, to minimise infection risk.³

Paracentesis can be performed in a hospice or in an ambulatory setting.

Technique^{1 2 4}

• Consider using ultrasound guidance when available. This can be used to confirm the presence of ascites and identify an area with a suitable volume of fluid for aspiration or drainage. Evidence suggests it reduces the risk of complications, particularly for large-volume paracentesis. Ultrasound can be either be used to mark a site for insertion, or in real-time to advance the needle or catheter under direct ultrasound guidance.

• Check that the correct equipment has been assembled:

  • Needles (25 gauge for infiltration, 22 gauge for fluid collection), syringes and local anaesthetic.

  • Antiseptic skin preparation and drapes.

  • For large-volume paracentesis: prepackaged plastic sheath cannulas are available - alternatively, a very wide bore IV cannula can be used; IV tubing and a drainage bag.

  • Adhesive tape.

  • Sterile gloves.

• Explain the procedure to the patient, including risks, and obtain consent.

• Position the patient, usually in the supine position. The lateral decubitus position can be used if there is a small volume of ascites.

• Position of the tap:
  

  • Locate area of flank dullness lateral to the rectus abdominis muscle and go approximately 5 cm superior and medial to the anterior superior iliac spines.

  • Avoid the inferior epigastric vessels which run up the side of the rectus abdominis to anastomose with the superior epigastric vessels coming down.

  • Avoid the pelvic area, solid tumour masses, prominent superficial veins (caput medusa) and scars (may have collateral vessels close by or adherent bowel beneath).

  • As above, ultrasound guidance may be helpful to identify a suitable site.

• Using the 25G needle, infiltrate local anaesthetic into the skin and subcutaneous tissues. Aspirate whilst advancing the needle. Remove the needle once the local anaesthetic has been applied.

• Using the 22G needle and a large syringe (for a diagnostic aspirate), or the IV cannula/ascitic drain catheter (for large-volume paracentesis), enter the anaesthetised puncture site at a perpendicular angle to the skin. Slowly advance the needle whilst aspirating. Once the tip of the needle enters the peritoneal cavity, you should feel a 'give', and fluid will be aspirated into the syringe.

  • For diagnostic purposes, 20-50mL of fluid should then be aspirated, and the needle removed afterwards.

  • For large-volume paracentesis, the cannula can now be advanced over the needle to lie in the peritoneal cavity, with the needle then removed and the cannula connected to tubing and a drainage bag.

• In both cases, the Z-track technique is helpful to reduce the risk of leakage. After puncturing the skin, apply traction to the skin caudally before advancing the needle; this means that the puncture site on the skin and the peritoneum are no longer adjacent when the needle/drain is removed.

• If a catheter or drain has been placed for large-volume paracentesis:

  • Document the time at which the drain should be removed by (usually within six hours).

  • Prescribe human albumin solution according to local guidelines; for example, 100mL of 20% human albumin solution to be given for every 2.5L of ascites drained.

  • Monitor the patient's vital signs; slow or stop the drainage if hypotension develops.

Aftercare

• Ascites may recur requiring repeated paracentesis.

• Look out for intraperitoneal infection - eg, signs of peritoneal irritation and fever.

Post-paracentesis circulatory dysfunction

Withdrawal of 5 L or more of ascites can precipitate post-paracentesis circulatory dysfunction (PPCD), leading to:

• Hepato-renal syndrome and hyponatraemia.⁸

• Acute kidney injury.

• Increased plasma renin activity.

Current guidelines suggest that albumin (as 20% or 25% solution) should be infused after paracentesis of ≥5 L is completed, at a dose of 8 g albumin/L of ascites removed. There is no conclusive evidence that albumin or artificial plasma expanders prevent complications or improve outcomes.⁹

Palliative care

The underlying disease is an important confounding factor and in terminal care, the prime concern must be patient comfort. In malignant ascites, paracentesis brings some relief to about 90% of patients. Where frequent drainage is required, a permanent drain can be left in place;¹⁰ although this increases the risk of infection, there is a notable reduction in symptom burden in most patients.

Long-term indwelling catheters for ascitic drainage in people with cirrhosis have traditionally been avoided due to concerns for infection. Preliminary data suggests they may have a relatively low rate of infective complications, although further high-quality studies are needed to establish safety and efficacy.¹¹