Abdominal paracentesis

Normally, the abdomen contains only a small amount of fluid. There are several pathological conditions that result in oedema, or excessive fluid accumulation in bodily tissues. “Ascites” is defined as an excessive amount of fluid built up within the abdominal (peritoneal) cavity. It is not a disease, but rather a symptom of the conditions such as: liver cirrhosis, malignancy (cancer or lymphoma), pancreatic diseases, heart failure, and less frequently, endocrine system disorders or kidney failure. Smaller amounts of the abdominal fluid usually do not produce symptoms, but if fluid retention is sufficiently severe, it can cause:

• rapid weight gain,
• abdominal distention and discomfort (see Fig. 1),
• shortness of breath and actual dyspnea, or difficulty breathing,
• swollen ankles.

[Reproduced, with permission, from: http://medicine.ucsd.edu/clinicalimg (Catalog of Clinical Images by Dr. Charles Goldberg, MD; © Regents of the University of California)]

By far the commonest cause of ascites seen in primary care or family/general practice is intra-abdominal malignancy. If there are doubts about the exact cause of the ascites [see ‘Indications for abdominal paracentesis’ below], diagnostic aspiration of the peritoneal fluid can be easily performed, and the fluid (usually less than 200 ml) sent for chemical analysis, Gram stain, culture and cytology (Brown JS, 1989) .
In many cases, with modern medical treatment (including bed rest, a low-salt diet, water restriction, and the use of diuretics), fluid removal is rather not necessary (Brown JS, 1989) .
In cases of refractory ascites (i.e. ascites that do not respond appropriately to sodium/water restriction and diuretic treatment), and because of the discomfort and respiratory difficulty accumulations of fluid can produce, therapeutic abdominal paracentesis is often the procedure of choice.
Paracentesis involves the removal of fluid from the abdominal cavity via a needle that is usually inserted into the peritoneum under local anaesthesia. This is a relatively safe and painless method of relieving fluid build-up. Nevertheless it is not necessary nor desirable to remove all the ascites since a severe hypotensive reaction may occur and such a procedure would rapidly deplete the patient of large quantities of protein (Brown JS, 1989) .
In therapy-resistant ascites even a large paracentesis (4-6 litres) can be safe provided that 6-8 g of albumin is infused intravenously for every removed litre of ascites (Kunnamo I (ed), 2005) .However, patients with liver cirrhosis and refractory ascites may also, and even better, temporarily benefit from transjugular intrahepatic portosystemic stent-shunts (TIPS) (Saab S, Nieto JM, Lewis SK, Runyon BA, 2006) .

Indications for abdominal paracentesis

A. Diagnostic

1. To determine the cause of ascites, including:
   • new onset ascites
   • ascites of unknown origin
   • suspected intra-abdominal haemorrhage from trauma
2. To obtain fluid for analysis and culture in patients with pre-existing ascites who are thought to have an infection (i.e. have fever, abdominal pain, hypotension or encephalopathy)

B. Therapeutic

1. To lower intra-abdominal pressure in large, tense ascites (causing gastrointestinal or cardiorespiratory symptoms): relief of pain, abdominal discomfort, and respiratory compromise
2. In patients with ascites refractory to medical management

Contraindications to paracentesis

1. Absolute: acute abdomen requiring immediate surgery
2. Relative:
   • Uncooperative patient
   • Severe bowel distension or bowel obstruction
   • Previous abdominal surgery (e.g. intra-abdominal adhesions)
   • Pregnancy (ultrasound guidance is preferred after the 1^st trimester) (Pfenninger JL, Fowler GC (eds), 2003)
   • Distended bladder that cannot be emptied with a Foley catheter
   • Infected skin or soft tissue at the intended site of puncture (e.g. abdominal wall cellulitis or abscess)
   • Uncorrected bleeding diathesis (i.e. coagulopathy or thrombocytopaenia)
   • Progressive liver failure with encephalopathy or hepatorenal syndrome

Severe bleeding diathesis should be corrected before performing paracentesis. Cautious paracentesis with a 22-gauge needle may be safely performed in patients with mild to moderate bleeding tendencies (Stone CK, Humphries R (eds), 2004) . Severe bowel distention can be corrected with nasogastric suction and a rectal tube if paracentesis must be performed.

It is very helpful to get an ultrasound scan of the ascites before the procedure (Dimov V, 2006) . The radiologist can mark the spot for paracentesis, and evaluate both the distance from the skin to the fluid (usually 1 cm) and the distance to the midpoint of the collection (usually 3 cm). It gives the operator an idea how deep he/she has to go with the needle when performing paracentesis (Dimov V, 2006) . Abdominal anatomy must be considered during the entire abdominal paracentesis procedure (Pfenninger JL, Fowler GC (eds), 2003) . It should be remembered that large volumes of ascitic fluid tend to float the air-filled bowel toward the midline when the patient is in supine position [see Fig. 2A below], and therefore the bowel can be more easily perforated during paracentesis. As the cecum is relatively fixed and less mobile than the sigmoid colon, bowel perforations are more frequent in the right lower quadrant than in the left (Pfenninger JL, Fowler GC (eds), 2003) . Before performing paracentesis, the diagnosis of ascites should be verified by gentle percussion, and then the patient turned very gently towards the chosen side. Repeat percussion should confirm the presence of shifting dullness (Fig. 2B).

Ascitic fluid will flow to the most dependent portions of the abdomen. The air-filled intestines will float on top of this liquid (A). The technique of shifting dullness makes use of this relationship in order to detect the presence of ascitic fluid (B). [Reproduced, with permission, from: http://medicine.ucsd.edu/clinicalimg (Catalog of Clinical Images by Dr. Charles Goldberg, MD; © Regents of the University of California)]

Complications

1. Hypotension after a large-volume paracentesis (also can occur due to vasovagal response). Removal of >1.0 l of fluid is more likely to result in hypotension due to rapid mobilization of fluid from intravascular space (Chen H, Sonnenday CJ, Lillemoe KD (eds), 2000) . It can be prevented and corrected by intravenous hydration and/or by giving intravenous 5% albumin as replacement (e.g. 250 ml per liter of fluid removed).
2. Bladder perforation – avoided by asking the patient to urinate before the procedure or by using a Foley catheter to empty the bladder.
3. Small and large bowel perforation
4. Stomach perforation
5. Lacerations of major vessels (mesenteric – resulting in intraperitoneal haemorrhage; inferior epigastric – leading to a haematoma of the rectus muscle sheath or the abdominal wall; iliac, aorta) – haemorrhage is usually self-limited; it can be avoided by entering the abdomen lateral to the rectus muscle (Chen H, Sonnenday CJ, Lillemoe KD (eds), 2000) , (Doherty GM, Lowney JK, Mason JE, Reznik SI, Smith MA, editors, 2002) .
6. Persistent leakage of ascitic fluid from the puncture site – especially in patients with large, recurrent ascites. It usually seals in less than two weeks, but can also result in peritonitis. Skin entry site may be sutured with figure ‘8’ stitch to minimize leak (Chen H, Sonnenday CJ, Lillemoe KD (eds), 2000) .
7. Abdominal wall haematoma
8. Infection (local or intraperitoneal) (Pfenninger JL, Fowler GC (eds), 2003)
9. Catheter fragment left in the abdominal wall or cavity (Dimov V, 2006)

Glossary

Pregnancy

is the carrying of one or more embryos or fetuses by female mammals, including humans, inside their bodies. In a pregnancy, there can be multiple gestations (for example, in the case of twins, or triplets). Human pregnancy is the most studied of all mammalian pregnancies.