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Paracentesis is a procedure in which a needle or catheter is inserted into the peritoneal cavity to obtain ascitic fluid for diagnostic or therapeutic purposes.[1, 2] Ascitic fluid may be used to help determine the etiology of ascites, as well as to evaluate for infection or presence of cancer. With regard to differentiation of transudate from exudate, the preferred means for characterizing ascites is the serum-ascitic albumin gradient (SAAG).
The SAAG is calculated by subtracting the albumin concentration of the ascitic fluid from the albumin concentration of a serum specimen obtained on the same day. The SAAG correlates directly with portal pressure. Transudative ascites occurs when a patient's SAAG level is greater than or equal to 1.1 g/dL (portal hypertension). Exudative ascites occurs when patients have SAAG levels lower than 1.1 g/dL. (See the Ascites Albumin Gradient calculator.)
Causes of transudative ascites include the following:
Causes of exudative ascites include the following:
Inflammation of the pancreas or biliary system
Ischemic or obstructed bowel
Spontaneous bacterial peritonitis
Infection of ascitic fluid without intra-abdominal infection usually occurs in patients with chronic liver disease due to translocation of enteric bacteria. Common pathogens include Escherichia coli, Klebsiella pneumoniae, enterococcal species, and Streptococcus pneumoniae. Patients with renal failure who use abdominal peritoneal dialysis are also at increased risk, as are children with nephrosis or systemic lupus erythematosus. Anaerobic bacteria are not associated with spontaneous bacterial peritonitis (SBP).
An ascitic fluid polymorphonuclear leukocyte (PMN) count higher than 250/μL (neutrocytic ascites), with the percentage of PMNs in the fluid usually greater than 50%, is presumptive evidence of SBP. Patients whose level meets these criteria should be treated empirically, regardless of symptoms. Secondary bacterial peritonitis is defined as infected ascitic fluid associated with an intra-abdominal infection.
Diagnostic tap is used for the following:
New-onset ascites - Fluid evaluation helps to determine etiology, differentiate transudate versus exudate, detect the presence of cancerous cells, or address other considerations
Suspected spontaneous or secondary bacterial peritonitis
Therapeutic tap is used for the following:
Respiratory compromise secondary to ascites
Abdominal pain or pressure secondary to ascites (including abdominal compartment syndrome)
An acute abdomen that requires surgery is an absolute contraindication.
Severe thrombocytopenia (platelet count <20 × 103/μL) and coagulopathy (international normalized ratio [INR] >2.0) are relative contraindications.
Patients with an INR greater than 2.0 should receive fresh frozen plasma (FFP) prior to the procedure. One strategy is to infuse one unit of fresh frozen plasma before the procedure and then perform the procedure while the second unit is infusing.
Patients with a platelet count lower than 20 × 103/μL should receive an infusion of platelets before the procedure.
In patients without clinical evidence of active bleeding, routine laboratory tests such as prothrombin time (PT), activated partial thromboplastin time (aPTT), and platelet counts may not be needed before the procedure. In these patients, pretreatment with FFP, platelets, or both before paracentesis is also probably not needed.
A study of 608 patients (72% with alcohol-related liver disease) found a low overall rate of complications that required transfusions (0.2%) and a higher incidence of significant hemoglobin drop among those with severe renal failure (creatinine > 6 mg/dL).
A prospective study of 171 patients undergoing paracentesis found that "major" complications occurred in 1.6% of procedures and included five episodes of bleeding and three infections, resulting in death in two cases. Major complications were associated with therapeutic but not diagnostic procedures and tended to be more prevalent in patients with low platelet counts (<50 × 109/L), patients who were Child-Pugh stage C, and patients with alcoholic cirrhosis.
Other relative contraindications include the following:
Distended urinary bladder
Abdominal wall cellulitis
Depending on the clinical situation, fluid may be sent for the following laboratory tests:
Gram stain - In a retrospective review of 796 peritoneal fluid samples, the evaluation of Gram stain results rarely provided clinically useful information for the detection of spontaneous bacterial peritonitis 
Cell count (elevated counts may suggest infection)
Total protein level
Triglyceride levels (elevated in chylous ascites)
Bilirubin level (may be elevated in bowel perforation)
Albumin level, used in conjunction with serum albumin levels obtained the same day (used to calculate SAAG; see the Ascites Albumin Gradient calculator)
Amylase level (elevation suggests pancreatic source)
Lactate dehydrogenase (LDH) level
After proper antiseptic preparation and local anesthesia, a diagnostic tap can be performed with a 10- to 20-mL syringe and an 18-gauge needle.
After proper antiseptic preparation and local anesthesia, a therapeutic tap can be performed with an intravenous (IV) catheter over the needle connected to drainage tubing.
In patients who are afebrile, alert, and have no other signs of bacterial peritonitis, ascitic fluid labs are often not necessary to rule out SBP).[8, 9]
To minimize the risk of persistent leak from the puncture site, use a small-gauge needle or take a "Z" track during insertion of the needle. (During removal of the needle, the subcutaneous tissue seals on itself.)
In a retrospective review of 796 peritoneal fluid samples, the evaluation of Gram stain results rarely provided clinically useful information for the detection of SBP.
Dietary sodium restriction and diuretics do not often provide symptomatic relief of refractory ascites in patients in advanced stages of cancer. Although paracentesis does effectively drain ascitic fluid, the condition invariably recurs, and repeated procedures are necessary. A 2008 study reported that a permanent peritoneal catheter to drain abdominal fluid greatly reduced the symptoms of ascites in these patients and avoided the costs and complications of frequent paracentesis procedures.
A meta-analysis suggests that the use of albumin in cirrhotic patients undergoing paracentesis reduces paracentesis-induced circulatory dysfunction and reduces death and renal impairment.
In cases with a persistent leak, a single skin suture might solve the problem. The application of an ostomy bag around the puncture site keeps the leak contained until it is eventually sealed off.
Postparacentesis hypotension is a delayed complication that may occur more than 12 hours after a procedure in which large volumes are taken off. Patients can be pretreated with a colloid solution, such as albumin, to decrease the frequency of this complication, though no difference in survival has been noted relative to other plasma expanders.
Timing of paracentesis
Whereas studies suggest that early paracentesis (<12 hours from admission) improves short term survival of hospitalized patients with SBP in comparison with delayed paracentesis, it seems that earlier administration of appropriate antibiotics in the early paracentesis group might have been a major contributing factor.[13, 14]
At this time and in the absence of prospective, randomized, controlled data, the authors recommend early diagnostic or therapeutic paracentesis and early empiric antibiotic administration in patient suspected of having SBP. When it appears that large-volume paracentesis is likely to be required, the authors suggest consideration of early small-volume paracentesis (ultrasound, syringe, and needle technique) followed by delayed and planned large-volume paracentesis (during hospitalization) under appropriate monitoring and hemodynamic support to minimize the risk of circulatory dysfunction induced by large-volume paracentesis.
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