Abdominal Paracentesis (Ascitic Tap)

Types

Indications

• New onset ascites (diagnostic workup)
• Suspected spontaneous bacterial peritonitis (SBP)
• To relieve cardiorespiratory and GI manifestations of tense ascites (therapeutic)

Contraindications

• Uncorrected coagulopathy with clinically evident fibrinolysis or DIC
• Bowel dilation or obstruction
• Pregnancy (technique must be modified - supraumbilical or US-guided approach)
• Abdominal hematoma, engorged veins, or superficial infection at the intended puncture site

Note: Routine coagulopathy (elevated PT, low platelets) is NOT a contraindication unless there is clinical evidence of active fibrinolysis or DIC. Studies show no increased bleeding risk with platelets >19,000/mm³ or PT <40 seconds.

Equipment

• Antiseptic solution + sterile drape
• Local anesthetic (lidocaine)
• 18-22 gauge needle (diagnostic) / 15-gauge steel or over-the-needle catheter (therapeutic)
• 20-50 mL syringe
• Vacuum bottles or drainage bag (for LVP)
• Blood culture bottles (for culture at bedside)

Site of Entry

1. Midline (primary) - 2 cm below umbilicus along the linea alba (avascular, fibrous)
2. Left/right lower quadrant (alternative) - 4-5 cm cephalad and medial to the anterior superior iliac spine, lateral to the rectus sheath (to avoid the inferior epigastric artery)

• Avoid midline if there is scarring, collateral veins, or previous complications at that site
• Left lower quadrant is generally preferred over right (less risk of cecal perforation)

Technique

1. Patient voids before the procedure
2. Position: supine (large ascites) or lateral decubitus (smaller amounts)
3. Clean the site with antiseptic; apply sterile drape; infiltrate local anesthetic

• With the non-needle hand, pull the skin ~2 cm caudally
• Insert the needle slowly while traction is maintained
• Once fluid flows, release the skin - the needle will angle caudally
• On withdrawal, displaced skin seals the tract, preventing persistent leaks

• Avoid continuous suction (attracts bowel/omentum, causing occlusion)
• If flow stops, gently rotate the needle and advance 1-2 mm
• Stabilize the needle once fluid is flowing freely

• Remove needle; apply adhesive bandage
• For persistent fluid leak: pressure bandage or cyanoacrylate adhesive; position the site non-dependently and apply pressure for 10 minutes first

Ultrasound Guidance

• Suspected adhesions or bowel obstruction
• Small or loculated fluid collections
• Patients at higher risk (prior abdominal surgery)

Volume of Fluid Removed

• Diagnostic tap: 20-50 mL sufficient
• Therapeutic LVP: Remove as much as possible without excessive manipulation; 5-6 L is routine and well tolerated; up to 10-12 L can be removed safely in most patients with chronic ascites
• For LVP >5 L: administer albumin infusion (6-8 g per litre removed) to prevent paracentesis-induced circulatory dysfunction (PICD)

Fluid Analysis (Send Routinely)

Serum-Ascites Albumin Gradient (SAAG)

• >1.1 g/dL → Portal hypertension (cirrhosis, CHF, Budd-Chiari, constrictive pericarditis)
• <1.1 g/dL → Non-portal hypertension cause (malignancy, TB, nephrotic syndrome, pancreatitis)

Complications

• Hyponatremia
• Renal dysfunction
• Hepatic encephalopathy
• Hemodynamic compromise (PICD after LVP)
• Significant bleeding, death (rare)

• Persistent ascitic fluid leak at wound site
• Abdominal wall hematoma
• Localized infection

• Perforation of vessels or viscera
• Generalized peritonitis
• Abdominal wall abscess

Causes of Ascites (for Context)

• Elevated hydrostatic pressure: Cirrhosis, CHF, constrictive pericarditis, IVC obstruction, Budd-Chiari syndrome
• Decreased osmotic pressure: Nephrotic syndrome, protein-losing enteropathy, malnutrition
• Fluid production exceeding resorption: Bacterial/TB/parasitic infections, neoplasms, hemorrhagic pancreatitis

Ascitic Fluid Findings: Malignant Ascites vs Portal Hypertension

The Core Test: SAAG (Serum-Ascites Albumin Gradient)

Diagnostic Algorithm

Detailed Comparison Table

Key Differentiating Points in Detail

1. SAAG - The Most Reliable Test

• Portal hypertension (cirrhosis, Budd-Chiari, cardiac): SAAG ≥ 1.1 g/dL
• Malignancy, TB, pancreatitis, nephrotic syndrome: SAAG < 1.1 g/dL
• Important caveat: If the patient has both cirrhosis AND liver metastases (massive hepatic involvement/pseudocirrhosis), the SAAG can paradoxically be ≥ 1.1 g/dL due to portal hypertension from tumour-induced changes - this represents ~one-third of malignant ascites cases

2. Total Protein - Separates Cirrhosis from Cardiac/Malignant

• Cirrhosis: protein < 2.5 g/dL (fibrosed sinusoids limit protein leakage)
• Cardiac ascites: protein ≥ 2.5 g/dL with SAAG ≥ 1.1 g/dL (normal "leaky" sinusoids congested by back-pressure)
• Malignant/TB ascites: protein ≥ 2.5 g/dL with SAAG < 1.1 g/dL (leakage from inflamed/obstructed peritoneal lymphatics)
• Protein < 1.0-1.5 g/dL in cirrhosis = higher SBP risk

3. Cytology - Diagnostic for Malignancy

• Sensitivity approaches 100% for peritoneal carcinomatosis
• Much lower sensitivity for malignancy causing ascites via liver metastases or lymphatic obstruction (not peritoneal seeding)
• Yield improves with larger submitted volume
• If cytology is negative but clinical suspicion remains high (low SAAG + high protein + no infection): next step is laparoscopy with peritoneal biopsy

4. Glucose & LDH

• In malignancy: glucose is reduced (tumor cell consumption); LDH ratio ascites:serum ≈ 1.0 (vs ~0.4 in uncomplicated cirrhosis)
• These same criteria (glucose < 50 mg/dL + LDH > serum ULN + protein > 1 g/dL) also suggest secondary bacterial peritonitis from bowel perforation - must be interpreted with clinical context

5. Gross Appearance

6. Cell Count Differential

• PMN predominance (≥ 250/μL): bacterial peritonitis (SBP or secondary)
• Lymphocyte predominance: tuberculous peritonitis, malignancy (lymphoma)
• For bloody ascites: subtract 1 PMN per 250 RBC to correct the count

Important Caveats & Pitfalls

• SAAG accuracy is reduced if samples are not taken simultaneously, if serum albumin is very low, or if ascites is chylous (falsely high SAAG)
• Serum hyperglobulinemia (>5 g/dL) narrows the albumin gradient falsely; correct with: SAAG × (0.16 × serum globulin + 2.5)
• CA-125 is elevated in ALL causes of ascites (not specific for ovarian cancer in this context) - do not use to diagnose malignant ascites
• CEA, fibronectin, cholesterol are nonspecific and unhelpful in distinguishing malignant ascites
• CT findings that suggest malignant ascites: fluid in the omental bursa, peritoneal thickening/enhancement, increased fluid density, loss of bowel loop mobility

Quick Summary: The 2-Step Rule

Step 1 - SAAG: ≥ 1.1 → portal hypertension pathway | < 1.1 → peritoneal process (malignancy/TB)

Step 2 - Ascites Protein: If SAAG ≥ 1.1 → protein < 2.5 = cirrhosis; protein ≥ 2.5 = cardiac/Budd-Chiari. If SAAG < 1.1 → send cytology, AFB/ADA; consider CT and laparoscopy