definition and pathophysiology
- Pathologic accumulation of fluid within peritoneal cavity.
- Results from increased hydrostatic and osmotic pressures within hepatic and mesenteric capillaries.
- Fluid transfer from blood vessels to lymphatics overcomes drainage capacity.
- Peripheral arterial vasodilation hypothesis: Portal hypertension causes splanchnic vasodilation, leading to decreased effective intravascular volume.
- Baroreceptors trigger renin-angiotensin-aldosterone (RAA) system and antidiuretic hormone release, driving renal sodium and water retention.
- Decreased plasma colloid osmotic pressure (hypoalbuminemia) further exacerbates fluid shift.
etiological classification
| Category | Specific etiologies |
|---|
| hepatic/portal hypertension | Cirrhosis, portal vein thrombosis, Budd-Chiari syndrome, congenital hepatic fibrosis, veno-occlusive disease. |
| hypoalbuminemia | Nephrotic syndrome, protein-losing enteropathy, severe malnutrition. |
| cardiac | Congestive heart failure, constrictive pericarditis. |
| fetal/neonatal | Meconium peritonitis (bowel perforation), parvovirus, urinary tract obstruction (uroascites), hydrops fetalis, biliary ascites. |
| chylous | Lymphatic malformations, trauma, thoracic duct injury, post-surgical. |
| infectious/inflammatory | Tuberculous peritonitis, pancreatitis, systemic lupus erythematosus. |
clinical evaluation
history
- Rapid weight gain, increasing abdominal girth, ankle edema.
- Neonatal umbilical catheterization (risk factor for portal vein thrombosis).
- History of gastrointestinal bleeding or unexplained splenomegaly.
physical examination
- Abdominal distension, bulging flanks, shifting dullness.
- Fluid thrill, puddle sign (dullness over umbilicus in prone position).
- Tense ascites associated with umbilical herniation.
- Liver disease stigmata: Jaundice, palmar erythema, spider angiomata, caput medusae (dilated abdominal collaterals).
- Cardiac evaluation: Markedly elevated jugular venous pressure indicates cardiac origin.
diagnostic investigations
imaging
- Abdominal ultrasound: Most sensitive modality for ascites detection.
- Differentiates ascites from obesity or pseudoascites (omental/ovarian cysts).
- Identifies portal hypertension signs: Splenomegaly, enlarged portal vein.
- Doppler evaluates hepatic vasculature flow and direction.
diagnostic paracentesis
- Indicated upon initial detection, hospitalization, or clinical deterioration (fever, pain).
- Ultrasound-guided tap recommended for loculated ascites.
- No contraindication for prolonged prothrombin time unless disseminated intravascular coagulation present.
ascitic fluid analysis
| Test | Findings | Interpretation |
|---|
| serum-ascites albumin gradient (SAAG) | ≥ 1.1 g/dL | Portal hypertension (cirrhosis, fulminant failure, Budd-Chiari). |
| SAAG | < 1.1 g/dL | Non-portal hypertensive (tuberculous peritonitis, nephrotic syndrome). |
| polymorphonuclear (PMN) count | ≥ 250 cells/mm3 | Spontaneous bacterial peritonitis (SBP). |
| lymphocyte count | Predominant lymphocytes | Tuberculous infection. |
| triglycerides | > 200 mg/dL, milky appearance | Chylous ascites. |
| amylase | Elevated ( > 5x serum level) | Pancreatitis or intestinal perforation. |
| bilirubin | > 6 mg/dL (greater than serum) | Biliary or proximal small intestinal perforation. |
| urea/creatinine | Higher than serum levels | Uroascites. |
management protocol
dietary modifications
- Sodium restriction: Mainstay of therapy. Limit to 1-2 mEq/kg/day for infants/children or “no salt added” diet.
- Fluid restriction: Rarely indicated unless severe hyponatremia (<125-130 mEq/L) present.
- High-protein, high-calorie diet improves serum albumin and oncotic pressure.
pharmacologic therapy
- Target optimal weight loss without intravascular volume depletion.
- Spironolactone: Aldosterone antagonist, first-line agent. Dose 2-5 mg/kg/day.
- Furosemide: Added for resistant ascites or to counteract spironolactone-induced hyperkalemia. Dose 0.5-2 mg/kg/day.
- Optimal diuretic ratio: 5 (spironolactone) to 2 (furosemide).
refractory ascites interventions
- Defined as ascites unresponsive to sodium restriction and maximal diuretic therapy.
- Large volume paracentesis: Performed for tense ascites causing respiratory distress or severe pain.
- Requires concurrent 20% albumin infusion (5 ml/kg) to prevent post-paracentesis circulatory dysfunction and rapid reaccumulation.
- Transjugular intrahepatic portosystemic shunting (TIPS): Diverts portal blood flow, decreases portal pressure. Used as bridge to transplant.
- Liver transplantation: Definitive treatment for ascites associated with end-stage liver disease, hypoalbuminemia, or recurrent SBP.
complications
spontaneous bacterial peritonitis (SBP)
- Spontaneous infection of ascitic fluid without intra-abdominal source.
- Pathogenesis: Bacterial translocation from gut to mesenteric lymph nodes, impaired immune clearance.
- Presentation: Fever, abdominal pain, unexplained clinical deterioration, encephalopathy.
- Diagnosis: Ascitic fluid PMN ≥ 250 cells/mm3.
- Treatment: Intravenous third-generation cephalosporins (e.g., cefotaxime, ceftriaxone) for 5-7 days.
- Prophylaxis: Long-term oral norfloxacin recommended after prior SBP episode.