Definition of Ascites
Ascites is the pathological accumulation of fluid within the peritoneal cavity, most commonly caused by portal hypertension in cirrhosis (75-85% of cases). 1, 2
Core Definition and Pathophysiology
Ascites represents fluid accumulation specifically in the peritoneal cavity, not in subcutaneous tissues or other compartments. 3
The condition develops when portal hypertension increases hydrostatic pressure at the sinusoidal level, combined with splanchnic arterial vasodilation and activation of sodium-retaining mechanisms (renin-angiotensin-aldosterone system, sympathetic nervous system, and arginine vasopressin). 1, 4
Portal hypertension triggers intestinal microvasculature to generate angiogenic factors, leading to portosystemic collateral development and further exacerbation of the hemodynamic abnormalities. 1
Clinical Grading System
Ascites severity is classified into three grades based on clinical presentation: 1, 5
- Grade 1 (Mild): Detectable only by ultrasound examination
- Grade 2 (Moderate): Causes moderate symmetrical abdominal distension with positive shifting dullness
- Grade 3 (Large/Tense): Causes marked abdominal distension, typically exceeding 5 liters of fluid
Physical Examination Findings
Shifting dullness becomes detectable when approximately 1,500 mL of free fluid accumulates in the abdomen, with 83% sensitivity and 56% specificity for detecting ascites. 1, 6, 5
Physical examination is unreliable in obese patients or when smaller fluid volumes are present, requiring ultrasound confirmation which can detect as little as 100 mL. 1, 5
Clinical Classifications
Uncomplicated Ascites
Ascites that is not infected and not associated with hepatorenal syndrome (HRS). 1
Refractory Ascites
Ascites that cannot be mobilized or recurs early after therapeutic paracentesis despite maximal medical treatment, including two subgroups: 1
- Diuretic-resistant ascites: Refractory to dietary sodium restriction and intensive diuretic treatment
- Diuretic-intractable ascites: Refractory due to diuretic-induced complications preventing effective dosing
Etiologic Classification by SAAG
The serum-ascites albumin gradient (SAAG) is the most accurate single test for classifying ascites etiology with 97% accuracy: 6, 7
SAAG ≥11 g/L indicates portal hypertension: 1, 6
- Cirrhosis (most common)
- Cardiac failure
- Portal vein thrombosis
- Hypothyroidism (limited data)
SAAG <11 g/L indicates non-portal hypertensive causes: 1, 6
- Peritoneal carcinomatosis
- Peritoneal tuberculosis
- Pancreatitis
- Bowel perforation
- Nephrotic syndrome
Critical Diagnostic Pitfalls
Do not confuse ascites with subcutaneous edema of the abdominal wall—these represent distinct fluid compartments requiring different diagnostic and therapeutic approaches. 3
Do not assume all abdominal distension is ascites—careful physical examination with shifting dullness testing and ultrasound confirmation are essential before proceeding to paracentesis. 6, 5
Do not delay diagnostic paracentesis in hospitalized patients or those with new-onset ascites—each hour of delay increases in-hospital mortality by 3.3% when spontaneous bacterial peritonitis is present. 1, 5