Hospital Medicine

Paracentesis

I. Problem/Challenge.

Of the many rules of thumb that the Hospitalist lives by, the old saying "where there is fluid, there should be a needle" is perhaps the most compelling reason for doing a paracentesis whenever a patient with ascites is sick enough to seek care in the emergency department and/or be hospitalized. Complications are relatively uncommon, and the data gathered will usually be helpful in caring for the patient. Sampling the ascites early in the admission will help rule out potentially fatal diseases, and will help to set up the differential diagnosis of the etiology of the fluid. The paracentesis should be done before antibiotics are given and without delay; each hour of delay has been shown to increase mortality.

II. Identify the Goal Behavior.

The paracentesis is a simple, relatively harmless sampling of any fluid in the abdominal cavity. One of the most important diseases to diagnose is spontaneous bacterial peritonitis (SBP). Since there are few absolute contraindications, the biggest risk by far is not doing the test when clinically indicated. Even though many patients with ascites will also have liver disease, thrombocytopenia and a coagulopathy, the use of fresh frozen plasma (FFP) and platelet transfusions is usually not necessary except in the conditions described below.

The main conditions that should prompt caution are patients with an added increase in bleeding risk, such as disseminated intravascular coagulation (DIC) or disorders of abnormal fibrinolysis; these patients may need platelets and fresh frozen plasma for DIC, or other agents such as aminocaproic acid or tranexamic acid for hyperfibrinolysis. In addition, care should be taken to avoid abdominal wall collaterals, the inferior hypogastric artery, and surgical scars (since such scars can have bowel attached immediately below them). Patients with bowel distension due to an ileus also present an increased risk, but image guidance with ultrasound (US) can be helpful in experienced hands.

Any patient with new ascites or ascites and related symptoms (i.e., encephalopathy, fever, abdominal pain) should get, at minimum, a diagnostic paracentesis (which is defined as collecting only enough fluid for diagnostic tests), as opposed to a therapeutic paracentesis (which involves draining enough fluid to make a symptomatic difference). Since up to 13% of patients with SBP are asymptomatic, a paracentesis should be considered in all hospitalized patients with ascites. A single large volume (≥ 5L) therapeutic paracentesis is useful for the treatment of tense ascites, but ascites is normally controlled with dietary sodium restriction and diuretics primarily; serial paracentesis is usually reserved for diuretic refractory ascites (along with treatment with transjugular intrahepatic portosystemic shunt [TIPS] and/or liver transplant).

At minimum, the following tests should be sent (followed by the most common colors of the tube they should be sent in):

  • Cell count and differential (purple top)

  • Albumin concentration (in ascites and serum) (red top)

  • Total protein (red top)

  • Culture (blood culture bottles, cultured at the bedside to increase yield minimize contamination, and increase time to detection)

  • Gram stain (red top)

Next, if there is fluid left over: glucose, LDH (in ascites and serum), amylase (in ascites and serum), and bilirubin (in ascites and serum, especially if the fluid is brown or dark orange) should be sent.

Finally, depending on the clinical scenario, one could send a tuberculosis smear (AFB) and culture, adenosine deaminase (ADA), cytology, triglyceride level, CEA/alkaline phosphatase, and a fungal culture (especially if the patient has a history of prophylactic antibiotic use, hepatorenal syndrome, or a high MELD score). Cytology and AFB smear and culture may be sent routinely, depending on the health system, or only when the pretest probability is high enough (i.e., exposure to tuberculosis [TB], a known cancer or mass, unexplained bloody ascites, etc.). The sensitivity of these TB tests is poor, so a laparoscopic biopsy is a better test if TB peritonitis is high on the differential.

These tests can be interpreted as such:

Polymorphonucleocytes (PMNs) are >250/mm3 --> then the patient has SBP and should be treated with antibiotics (see SBP chapter); antibiotics should be modified when culture data returns. Most patients will not need a repeat paracentesis, but if the patient is not improving a repeat paracentesis can be performed and/or a search for another cause of the infection may be necessary, such as secondary peritonitis that may need surgical correction.

If the culture returns negative, then the patient has culture-negative neutrocytic ascites (CNNA), and should be treated with antibiotics. If the PMN's are <250/mm3 but the culture returns positive with a single organism, then the patient has monomicrobial non-neutrocytic bacterascites (NNBA); consider this entity a precursor state of SBP, follow closely and treat if the patient has characteristic symptoms (fever, abdominal pain, unexplained encephalopathy) and/or their culture doesn't clear. Other symptoms and signs that are associated with SBP include: diarrhea, hypotension, hypothermia, ileus, elevated WBC, acidosis, worsening renal function. Polymicrobial bacterascites is often caused by a traumatic paracentesis.

Regardless of the PMN count, any patient with ascites, abdominal pain, unexplained encephalopathy, and/or fever should be empirically treated with antibiotics while awaiting the culture results.

SAAG (serum-to-ascites albumin gradient) <1.1 g/dl --> then the patient has ascites that is not due to portal hypertension, such as can be seen in peritonitis (tuberculosis, bacterial peritonitis/bowel rupture, fungal peritonitis, HIV-associated peritonitis), peritoneal carcinomatosis, pancreatitis, vasculitis, hypoalbuminemic states (nephrotic syndrome, protein-losing enteropathy, severe malnutrition and anasarca), Meig's syndrome (ovarian tumor), postoperative lymphatic leak, bowel obstruction or infarction.

SAAG (serum-to-ascites albumin gradient) > 1.1 g/dl --> then the patient likely has ascites due to portal hypertension, such as can be seen in cirrhosis, acute hepatitis (such as in alcoholic hepatitis), right-sided heart increased filling pressures (congestive heart failure, tricuspid regurgitation, constrictive pericarditis), massive hepatic metastasis, Budd-Chiari syndrome, portal or splenic vein thrombosis.

  • SAAG >=1.1 and total protein >= 2.5 g/dl --> cardiac ascites

  • SAAG >=1.1 and total protein < 2.5 g/dl --> cirrhosis

  • Ascitic total protein < 1.0 g/dl --> high risk of SBP (so consider daily antibiotic prophylaxis if there is also evidence of impaired renal function or liver failure).

  • Ascitic total protein <1.0 g/dl --> even higher risk of SBP (consider antibiotic prophylaxis while the patient is hospitalized)

Abdominal triglycerides are > serum triglycerides and > 200 mg/dl --> then the patient has chylous ascites (usually "milky" in appearance), due to disruption of the lymphatic system (as can be seen in malignancy or trauma). Some ascites is “opalescent” due to an only slightly elevated triglyceride level.

Bilirubin in ascites is ≥ 40% of serum ascites --> then there is a significant jaundice, but if the ascites bilirubin is greater than serum bilirubin, then there is likely a ruptured gallbladder or a perforated duodenal ulcer.

LDH in ascites is ≤ 40% of LDH in serum --> patient has uncomplicated ascites

LDH in ascites is > 40-100% of LDH in serum --> patient probably has SBP

LDH in ascites is > 100% of LDH in serum --> patient probably has an infection, tumor or bowel perforation.

Amylase in ascites is ≤ 40% of amylase in serum --> then the patient has uncomplicated ascites

Amylase in ascites is > 40% of amylase in serum --> patient may have “pancreatic ascites” (especially if the amylase is > 2000 IU/L) or, even more concerning, a gut perforation.

Distinguishing SBP from secondary bacterial peritonitis (i.e., due to bowel perforation, or non-perforation peritonitis as can be seen with an intra-abdominal abscesses) is crucial because the latter may need to be treated surgically. CEA > 5ng/ml and alkaline phosphatase >240 units/liter suggests that the gut has perforated into the ascitic fluid (sensitivity 92% and specificity 88%). Another method to determine this is if 2 out of the 3 are found (Runyon's criteria): 1) Total Protein >1 g/dl; 2) Glucose <50mg/dl; 3) LDH > upper limit in serum (usually 225 U/L); sensitivity 67% and specificity 96%. A polymicrobial culture result may also suggest bacterial infection secondary to gut perforation.

III. Describe a Step-by-Step approach/method to this problem.

1. Collect supplies: consent form and lab slips (filled out ahead of time), sterile gown, sterile gloves, mask, eyewear, hat, chucks, extra gauze squares, a sterile drape, paracentesis kit (such paracentesis kits usually have other necessary equipment such as a skin sterilizer, alcohol wipes, labels, lidocaine 1%, skin anesthesia needles, #11 blade scapel, adhesive bandage, etc.), tubes (red top for albumin/protein, purple top, blood culture bottles, another red top for gram stain and/or fungal cultures as these can't be done off of the blood culture bottles), special container for add-on tests (i.e., cytology - goal is >30cc), enough vacuum bottles for the amount of fluid being taken off therapeutically. A 60cc syringe with a 1 to 1.5 inch needle (from 18-gauge to 22-gauge, using the narrowest needle possible) can be enough for a diagnostic tap, unless the patient is obese as then a lumbar puncture needle may be necessary. Position the sharps box strategically so as to avoid walking across the room with an open needle to dispose of it.

2. Consent the patient (complications include bleeding, infection, bowel damage - all usually <1%), and ask them to empty their bladder. They do not need to be NPO.

3. Consider using ultra-sound guidance (especially if this is a second attempt after an initial failure, or if the patient has significant scarring or adhesions). Paracentesis can be safe without US guidance, but one retrospective study found that the risk of bleeding dropped from 1.25% to 0.27% with US guidance.

4. Position the patient (supine with the head of the bed at 35%) and mark out the site (usually 2-3 cm superior and medial to the anterior superior iliac spine).

5. Position chucks, open the kit, and prep the site with povidone-iodine (Betadine) or chlorhexidine.

6. Wash hands and gown up, then place sterile drape.

7. Anesthetize skin and peritoneum (a 5cc syringe with a 25-gauge needle and 1% lidocaine often works well, though techniques vary).

8. Whether using a needle and syringe for a diagnostic tap or a catheter for a therapeutic tap, be sure to use a Z-technique on insertion. This can be done by first making a scalpel nick to the skin, inserting the needle to the subcutaneous level and applying 2 cm of horizontal traction on the skin, then finally entering the peritoneum. This will make the path of insertion travel at an angle once the needle is removed, thereby decreasing the chance of fluid leakage after the procedure is done. Be sure to aspirate while advancing the needle.

9. Drain the amount of fluid needed, remove the needle and place fluid into the various test tubes. Be sure to avoid needle sticks while inserting the needle into test tubes.

10. Write procedure note. Patient should lie flat for 1-2 hours.

11. Consider giving albumin for large volume paracentesis at a dose of 6-8 grams per liter of ascites removed (50 grams max), divided into two doses, one given immediately after and the other at 6 hours. The use of albumin remains controversial with many experts feeling that removing 5 liters or less does not need albumin.

IV. Common Pitfalls.

Confused patients with end-stage liver disease are often initially given a diagnosis of hepatic encephalopathy due to “missing a dose of lactulose.” However, the hospitalist needs to have a heightened concern for underlying SBP as a trigger for hepatic encephalopathy, particularly if the patient has abdominal pain or fever; if they do, a paracentesis should be done in the ED or immediately on the floor, and then antibiotics should be given without delay.

Even if the SAAG is ≥1.1 g/dl, suggesting portal hypertension, there might also be another concurrent process, such as carcinomatosis or tuberculosis. Patients with risk factors (i.e., older women with an ovarian mass; patients from areas where tuberculosis is endemic), should have the appropriate tests sent as per the clinical scenario, such as a cytology and AFB/culture.

A patient with ascites will have an unpredictable abdominal exam for bowel perforation because involuntary guarding or rebound may be difficult to determine if the abdomen is tense. If bowel perforation is suspected, Total Protein, Glucose, LDH, or CEA and Alk Phos should be checked. A perforation can then be confirmed with a computed tomography (CT) of the abdomen, and surgery should be called early as they may opt to do an exploratory laparotomy.

There are a number of procedural issues that might arise during or after the procedure. The following is a list of advice on what to do in each situation:

1. No fluid is aspirated once the needle is placed --> remove the needle and have the ascites marked out by ultrasound before attempting again. A catheter with more side-holes may work better.

2. Bloody fluid is aspirated --> may be indication of ascites associated with a malignancy, hemorrhage, or bleeding from a collateral that had been speared. Does the patient have a clotting disorder such as DIC? Consider correcting coagulation tests before, or after, the procedure. The patient may need surgery to stop the bleeding, or an embolization procedure in interventional radiology (if available). Be sure to correct the PMN count in your calculations: one WBC is subtracted from the absolute WBC count for every 750 red cells/mm3, and one PMN is subtracted from the absolute PMN count for every 250 red cells/mm3.

3. Feculent material is aspirated --> withdraw needle and have another site marked out by ultrasound. Follow the patient closely for signs of peritonitis, and have a low threshold for starting antibiotics, getting imaging, and calling a surgery consult.

4. The plastic catheter broke during the procedure --> it is possible that a piece of the plastic was sliced off by the needle tip if it was replaced during the procedure. The patient may need a laparoscopic procedure, or a laparotomy, to retrieve the plastic piece; patients with ascites may not do well with such a procedure. This has led many medical groups to use metal catheter kits over plastic ones.

5. Fluid leaks from the insertion site --> usually due to an improperly inserted needle, not using the Z-technique. Place an ostomy bag to collect the fluid; it will usually stop within a few days, but watch for the development of cellulitis. The patient may need another paracentesis in another site to relieve pressure off of the primary site.

V. National Standards, Core Indicators and Quality Measures.

No national standards/benchmarks established yet.

VI. What's the evidence?

Runyon, BA.. "Management of Adult Patients with Ascites Due to Cirrhosis: An Update.". Hepatology. vol. 49. 2009. pp. 2087-2107.

Dever, JB,, Sheikh, MY.. "Review article: spontaneous bacterial peritonitis–bacteriology, diagnosis, treatment, risk factors and prevention.". Alimentary pharmacology & therapeutics.. vol. 41. 2015. pp. 1116-31.

Gaetano, JN,, Micic, D,, Aronsohn, A,, Reddy, G,, Te, H,, Reau, NS,, Jensen, D.. "The benefit of paracentesis on hospitalized adults with cirrhosis and ascites.". Journal of gastroenterology and hepatology.. vol. 31. 2016. pp. 1025-30.

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