Paracentesis and Ascites Fluid Analysis
Stephen Y. Chang, M.D.
June 16, 2002
THE PROCEDURE:
A relatively simple bedside procedure in which one inserts a needle into the abdomen,
thereby evacuating either a small amount of ascites fluid for diagnostic purposes, or large
amounts of fluid for therapeutic purposes.
It is the most cost-effective means of determining the cause of ascites.
INDICATIONS:
1. Above all, anyone (in- or outpatient) with new-onset ascites should have at least
a diagnostic paracentesis.
2. Many authors advocate tapping anyone admitted to the hospital with ascites.
3. Anyone with ascites who is showing signs/symptoms of infection, especially
fever, hypotension, peripheral leukocytosis, encephalopathy, acidosis.
CONTRAINDICATIONS:
Really, very few contraindications at all.
1. Coagulopathy stands as one relative contraindication, but keep in mind that most
cirrhotics with ascites have a concomitant coagulopathy (reflected by an elevated
INR). Very few of them will bleed unless the needle actually enters a blood vessel
(which is a rare event). Incidentally, there are NO studies to support giving FFP or
other blood products prior to paracentesis to reduce bleeding complications.
2. DIC or evidence of fibrinolysis is considered by some authors to be an absolute
contraindication to paracentesis.
RISKS:
When you talk with the patient or proxy to get consent for the procedure, remember to
discuss with them the following risks of the procedure:
1. Abdominal wall hematoma (rare, only about 2% of cases in some studies)
2. Infection (also extremely rare to get it from paracentesis; some studies report
ZERO infections related to the procedure)
3. Bleeding
There have been studies of paracentesis complications, and none of them report any
deaths associated with the procedure itself.
TOOLS:
You’ll need the following…
1. A large bore Angiocath needle (around 16-18 gauge usually suffices for large
volume taps; 20-22 is fine for a diagnostic). Avoid the short Angiocaths (less than
3.5 inches), as these often won’t be long enough to get good access into the
peritoneal space
2. A thoracentesis kit. Out of this, you will use the long tubing provided to drain
fluid into collection bottles in large volume paracentesis. And, in the occasional
situations where an Angiocath is not effective, you may need to use the ‘harpoon’
long needle used in thoracentesis for access instead.
Always make sure you familiarize yourself with the instruments in the kit and how
the stopcocks work before you start your procedure!
3.
4.
5.
6.
Betadine and sterile gauze
1 or 2% Lidocaine and a 25 gauge needle and 5cc syringe for infiltration
Chux to keep the bed clean
A gown and mask for yourself (the fluid is often under pressure, and it can spurt
out the needle a good distance!). Always remember that with any procedure, you
should be wearing eye/splash protection.
7. Sterile gloves
8. Collection bottles – if doing a large volume paracentesis, you may need up to 6-7
bottles (1 liter each)
TECHNIQUE
1. Get consent from either the patient or the patient’s health care proxy.
2. Position the patient, either supine or, more commonly, in the lateral decubitus
position favoring the side where you intend to insert the needle. The usual sites to
tap are RLQ or caudal to the umbilicus (if the patient is thin).
3. Elevate the head of the bed slightly
4. Percuss the abdomen to determine where the fluid level exists
5. Clean the skin thoroughly with Betadine solution
6. Infiltrate the skin and subcutaneous tissues with lidocaine via the 25 gauge needle
and wait about 3-5 minutes for the lido to take effect.
7. Insert the Angiocath or thoracentesis needle with a syringe attached at your
chosen site perpendicular to the skin. As you advance your needle slowly, aspirate
intermittently until you get fluid return. Continuous aspiration has the theoretical
risk of vacuum suctioning bowel and omentum towards the needle.
8. Once flow is obtained, remove the needle leaving the catheter in place. Collect at
least 20-30cc for your lab tests and cultures (into blood culture bottles – 5-10cc’s
each bottle).
9. If performing a therapeutic paracentesis, then disconnect your syringe and attach
the tubing to the catheter, with another needle at the other end of the tubing. This
needle is used to insert into the vacutainer collection bottles (1 liter each).
TECHNIQUE (con’t) :
Remember to send at least the following routine ascites labs:
1. Cell count and differential
2. LDH
3. Albumin
4. Culture in blood culture bottles inoculated at the bedside
ALSO remember to send a serum LDH and albumin at the same time (or at least from the
same day)!!!
INTERPRETING ASCITES FLUID
Cell Count:
 There is no ‘standardized’ ascites fluid cell count
 Generally accepted ‘cut-off’ for upper-limits of normal for infection is less than
250 PMNs/mm3
 PMNs usually constitue 70% of the cell count. In spontaneous bacterial
peritonitis, for example, PMNs are the predominant line. In tuberculous ascites,
you’ll see a lymphocytic predominance.
 Bloody ascites fluid is usually the result of the procedure itself, ie traumatic tap
The Serum-Ascites Albumin Gradient:
 The concept surrounds oncotic-hydrostatic balance
 Simple calculation: Serum albumin – Ascites albumin= SAAG
SAAG > 1.1 mg/dl
SAAG < 1.1 mg/d
Cirrhosis
Alcoholic Hepatitis
Cardiac Ascites
“Mixed Ascites”
Massive Liver Metastasis
Fulminant Hepatic Failure
Budd-Chiari Syndrome
Portal Vein Thrombosis
Veno-Occlusive Disease
Myxedema
Fatty Liver of Pregnancy
Peritoneal Carcinomatosis
Tuberculous Peritonitis
Pancreatic Ascites
Bowel Obstruction
Biliary Ascites
Nephrotic Syndrome
Posteroperative Lymphatic
Leak
Serositis in Connective Tissue
Disease
Reproduced from Feldman et al, ed: Sleisenger and Fordtran’s Gastrointestinal and Liver Disease, 6th edition
Exudates, Transudates and Ratios:



We are always taught in medical school that the serum:ascites LDH and protein
ratios help differentiate exudates and transudates
The literature shows that these calculations are actually not all that helpful,
surprisingly.
The SAAG has become more favored in helping to characterize ascites fluid.
Amylase:


“Normally” in ascites, you see an ascites amylase that’s about half the serum
amylase
If the ascites is secondary to pancreatitis or perforated viscus, the amylase levels
can be as great as five-fold higher than the serum levels
Glucose:


In uncomplicated ascites, usually similar to serum levels.
In later SBP (but often not in early), ascites glucose levels can drop to as low as
zero mg/dl secondary to bacterial consumption
Cultures and Gram Stains:


Cultures should be obtained by inoculating blood culture bottles at the bedside.
This has been shown to improve sensitivity to at least 80%, compared with 50%
for ‘conventional’ culture methods.
Gram stains are relatively useless on ascites fluid – about as useful as asking for a
Gram stain on blood cultures to look for bacteremia. The concentration of
organisms just won’t be high enough to see something on Gram stain.
Cytology



Truly only helpful in diagnosing peritoneal carcinomatosis. Reported sensitivities
up to 100%.
Does not detect most other intra-abdominal cancers, mainly because most of the
other cancers do not frequently metastasize to the peritoneum.
Think of cytology as helping you only if you’re suspicious of a cancer that has
spread to the peritoneum. And remember that a negative cytology does not rule
out cancers such as hepatocellular carcinoma or liver metastases, which
commonly cause ‘malignant ascites.’