Ascites Tapping

Also known as paracentesis

A more general discussion of Ascites is found elsewhere, including the medical management. Tapping of ascites is a simple technique that can be used for diagnostic or therapeutic purposes. For the cancer patient, it is primarily palliative but in cirrhosis it can serve as an important bridge in the wait for a liver transplant.

1. Diagnostic:
   • New onset ascites:
     • To determine aetiology.
     • To differentiate transudate versus exudate.
     • To detect cancerous cells.
   • Suspected spontaneous or secondary bacterial peritonitis
2. Therapeutic:
   • To relieve respiratory distress secondary to ascites.
   • To relieve abdominal pain or pressure secondary to ascites.

• Uncooperative patient
• Skin infection at the proposed puncture site
• Pregnancy
• Severe bowel distension
• Coagulopathy (opinion divided - some feel only precluded where there is clinically evident fibrinolysis or DIC)

Prior to tap

Before tapping, there are certain investigations that should be undertaken. A more lenient approach is permissible if it is part of palliative care for advanced cancer.

• FBC and clotting screen
  There are no data to support the use of fresh frozen plasma before paracentesis although if thrombocytopenia is severe, most clinicians would give pooled platelets to reduce the risk of bleeding.
• U&E, creatinine, LFTs including plasma proteins.
• Abdominal ultrasound - reviewing 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.

Note, in patients receiving palliative care, it is important not to be excessive in investigations. A protocol for such care from Plymouth allows ultrasound to be reserved for cases of diagnostic uncertainty.³

Following the tap⁴

After a diagnostic tap the following investigations may be requested:

• Albumin or protein levels: Traditionally used to decide whether ascites is an exudate (>25g/l) or a transudate. The serum ascites-albumin gradient (SA-AG) is a better measure.
  

  SA-AG = serum albumin concentration - ascitic albumin concentration SA-AG ≥11g/l : likely causes - cirrhosis, cardiac failure, nephrotic syndrome SA-AG <11g/l : likely causes - malignancy, pancreatitis and tuberculosis

• Microscopy:
  • Neutrophil Count: All patients should be screened for spontaneous bacterial peritonitis (SBP), which occurs in approximately 15% of patients with cirrhosis and ascites admitted to hospital.⁵ An ascitic neutrophil count of >250 cells/mm³ is diagnostic of SBP in the absence of a known perforated viscus or inflammation of intra-abdominal organs.
  • Red Cell Count: The concentration of red blood cells in cirrhotic ascites is usually <1,000 cells/mm3 but bloody ascitic fluid (>50,000 cells/mm³) occurs in about 2% of cirrhotics. In about 1/3 of cirrhotics with bloody ascites, there is an underlying hepatocellular carcinoma.
    In 50% of patients with bloody ascites, no cause can be found.
• Amylase: In pancreatic ascites the amylase in the fluid will be markedly raised.
• Culture and sensitivity: Preferred method is to inoculate blood culture bottles with ascitic fluid at the bedside.
  Several studies have shown that inoculation of ascitic fluid into blood culture bottles will identify an organism in approximately 70% of SBP cases whereas sending ascitic fluid in a sterile container to the laboratory will only identify an organism in about 40% of cases of SBP. Gram stain of ascitic fluid is rarely helpful.
• Cytology: Cytological examination is 60-90% accurate in the diagnosis of malignant ascites, especially when several hundred millilitres of fluid is tested and concentration techniques are used. It is not so valuable for the diagnosis of primary hepatocellular carcinoma.

In general, paracentesis can be thought of as a relatively safe procedure but it is usually performed on very sick patients, so that complications are reasonably common. Current British Guidelines considers the risk of serious complication as about 1 in 1000.⁴ Risks include:²

• Significant bleeding
• Infection
• Renal failure
• Hyponatremia
• Hepatic encephalopathy
• Complicated bowel perforation
• Paracentesis leak

Although usually undertaken in a hospital or hospice setting, one study found a complication rate of about 20% when the procedure was done at home.⁶

• Paracentesis for symptom relief is usually only undertaken with tense ascites; limit frequency to that necessary to keep the patient comfortable.
• A major risk is the introduction of infection into the peritoneal cavity - ensure aseptic technique and limit catheter drainage time to less than 6 to 8 hours (some authorities suggest 4 hours).
• If repeated tapping is part of palliative care, it can be performed in a hospice or the patient's home provided that sterile precautions are taken. It is not imperative to admit the patient to hospital.

• Check the correct equipment has been assembled:
  • Needles (25G for infiltration, 22G for fluid collection), syringes and local anaesthetic
  • Antiseptic skin preparation (value unproven) and drapes
  • A very wide bore IV cannula, IV giving set and a urine bag of the type attached to a catheter
  • Adhesive tape
  • Surgical gloves
• Explain the procedure to the patient, including risks, and obtain consent.
• The patient is usually in the supine position with the head of the bed elevated to allow fluid to accumulate in the patient's lower abdomen. Ensure that the patient has urinated prior to the procedure. Patients with only mild ascites may need to be positioned in the lateral decubitus position which enables air-filled loops of bowel to float away from the fluid level.
• Examine the abdomen to decide where (and where not) to make the tap:
  • The ideal site is controversial, either:
    • A midline site 2 cm below the umbilicus, through the linea alba, or,
    • Into an area of flank dullness lateral to the rectus abdominus muscle, approximately 5 cm superior and medial to the anterior superior iliac spines.
  • Whilst the mid-line is a fairly avascular area and in the past was favoured, there is danger that the bladder may be fuller than expected. Also the abdominal wall is thicker and the depth of the ascites shallower at the midline than in the left lower quadrant in the supine position.
  • The inferior epigastric vessels run up the side of the rectus abdominis to anastomose with the superior epigastric vessels coming down. The typical patient with ascites does not have well demarcated abdominal muscles and so keep well lateral without entering the pelvis.
  • Avoid solid tumour masses.
  • Avoid areas of prominent superficial veins (caput medusa).
  • Avoid scars as there may be collateral vessels or adherent bowel beneath them.
• Having decided on the site, clean and infiltrate the skin and then the deeper layers with local anaesthetic. Finally, move the needle down (usually 22G) into the ascitic fluid and draw back:
  • If typical straw-coloured fluid is not aspirated than another site must be chosen. (Some favour ultrasound guidance to identify the ideal site for blind puncture, particularly in small or moderate ascites, or following failed attempts.)
  • If the tap is purely diagnostic, attach a large, new syringe and 10-20 ml of fluid can be aspirated.
  • If a therapeutic tap is required to withdraw a much larger volume, continue as below.
• The needle of an IV cannula is usually inserted using the Z track technique in which the skin is penetrated perpendicularly, the needle is advanced obliquely in subcutaneous tissue and then the peritoneal cavity is punctured with the needle pointing perpendicular to the abdominal wall. This will ensure that the puncture site on the skin and the peritoneum do not overlie each other.
• When the needle enters the peritoneal cavity, there is a reduction in resistance. Partially withdraw the inner needle and push the cannula in a little further. Withdraw the inner needle and there should be a free flow of fluid.
• Attach the cannula to the giving set and the giving set to the urinary bag.
• Check fluid is flowing freely and tape the cannula to the skin. Try to position it so that the cannula is at right angles to the skin to permit free drainage.

• All ascitic fluid should be drained to dryness in a single session as rapidly as possible over 1-4 hours, assisted by gentle mobilization of the cannula or turning the patient on to the side if necessary.
• Expert opinion is that swift drainage is safest but if the patient develops symptoms of hypotension then the blood pressure should be checked and, if necessary, the drainage slowed or stopped.
• When drainage ceases or after 6-8 hours at the most, the catheter is gently withdrawn and the hole closed with a single suture or simple adhesive bandage.

Removal of large volumes

• Large volumes, even in excess 10 litres, over 2-4 hours may be removed.
• This causes a marked reduction in intra-abdominal and inferior vena cava pressure, leading to an increase in cardiac output. These haemodynamic changes are maximal at 3 hours. Pulmonary capillary wedge pressure decreases at 6 hours and continues to fall further in the absence of colloid replacement. On average, blood pressure decreases by about 8 mm Hg.⁷
• After withdrawal of 5 litres or more, patients are at risk of post-paracentesis circulatory dysfunction (PPCD). This is characterised by:
  • Hyponatraemia
  • Azotaemia (renal failure with uraemia)
  • Increased plasma renin activity
• It may be safe to omit plasma expansion if less than 5 litres is withdrawn but 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.⁴
• There is debate about the relative value of albumin or artificial plasma expanders but trials to date have been inadequately powered to answer the question and no statistical advantage has been found for either in preventing significant complications.²
• The Plymouth protocol for ascitic tap in palliative care patients suggests up to 5 litres can be removed at a single time, leaving drains for no more than 6 hours and giving IV fluids only when indicated.

• Within 48 hours, blood tests should be repeated although with terminal care, such rigidity is not always necessary.
• Ascites will tend to re-form and can be tapped again.
• A major concern is the introduction of infection. This may not be associated with signs of peritoneal irritation and so if the temperature rises over the next few days, then antibiotics should be given to cover such infection.
• If a large amount of protein has been removed, a high protein diet is in order - draining ascites may have relieved pressure on the stomach but the underlying condition is usually such that appetite remains poor.

• In the 1950s the introduction of potent diuretics made the tapping of ascites seem crude and dangerous but a review in 1990 suggested that it is both safe and effective.⁸
• Controversies have existed about the volume that may safely be tapped, the rate of removal and the simultaneous use of intravenous albumin. The underlying disease is an important confounding factor and in terminal care, the prime concern must be patient comfort.
• Most studies have looked at patients with cirrhosis where volumes as large as 4-6 litres a day can be safely withdrawn as long as intravenous albumin is given. In one study,⁹ up to 10 litres of fluid was safely removed in about an hour.
• In malignant disease, tapping ascites bring some relief to about 90% of patients.¹⁰ Where frequent drainage is required, a permanent drain can be left in place with an increased risk of infection but reduction in symptom burden in most patients.¹¹
• An alternative is a peritoneovenous shunt but blockage occurs in about a quarter and, in cirrhosis, it increases mortality.¹² In patients with advanced cancer, it does increase discharge from hospital rates compared to repeated ascitic tap.¹³