What is ascites?

Ascites: Definition and Classification

Ascites is a peritoneal effusion, defined as the pathological accumulation of fluid within the peritoneal cavity. 1, 2

Definition and Characteristics

Ascites represents an abnormal collection of serous fluid in the peritoneal space. This condition is most commonly associated with:

• Portal hypertension due to liver cirrhosis (75% of cases)
• Malignancy (10%)
• Heart failure (3%)
• Pancreatitis (1%)
• Other causes (11%) 2

Clinical Detection

• Physical examination: Shifting dullness is the preferred examination technique with 83% sensitivity and 56% specificity
• Approximately 1.5 liters of fluid must accumulate before shifting dullness becomes detectable
• Abdominal ultrasound may be required to confirm ascites, particularly in obese patients 1, 2

Classification of Ascites

Ascites is classified based on severity:

1. Grade 1 (Mild): Detectable only by ultrasound examination
2. Grade 2 (Moderate): Causes moderate symmetrical distension of the abdomen
3. Grade 3 (Large/Severe): Causes marked abdominal distension 1, 2

Additionally, ascites can be categorized based on treatment response:

• Uncomplicated ascites: Not infected and not associated with hepatorenal syndrome
• Refractory ascites: Cannot be mobilized or recurs rapidly despite maximal therapy
  • Diuretic-resistant: Refractory to dietary sodium restriction and intensive diuretic treatment
  • Diuretic-intractable: Refractory due to diuretic-induced complications 1

Diagnostic Evaluation

The serum-ascites albumin gradient (SAAG) is the most important diagnostic test for determining the cause of ascites:

• SAAG ≥1.1 g/dL: Indicates portal hypertension (97% accuracy)

  • Cirrhosis
  • Cardiac failure
  • Portal vein thrombosis
  • Massive liver metastases

• SAAG <1.1 g/dL: Indicates causes unrelated to portal hypertension

  • Peritoneal carcinomatosis
  • Tuberculosis peritonitis
  • Pancreatitis
  • Bowel perforation
  • Nephrotic syndrome 1, 3

Additional diagnostic tests include:

• Cell count and differential
• Total protein concentration
• Culture (when infection is suspected)
• Optional tests: cytology, amylase, glucose, lactate dehydrogenase (when indicated by clinical context) 1, 4

Pathophysiology

The development of ascites in cirrhosis involves:

• Portal hypertension leading to splanchnic arterial vasodilation
• Activation of the sympathetic nervous system and renin-angiotensin-aldosterone system
• Renal sodium retention and impaired free water clearance
• Bacterial translocation and systemic inflammation contributing to organ dysfunction 1

In conclusion, ascites is definitively a peritoneal effusion, representing an abnormal accumulation of fluid in the peritoneal cavity with various etiologies, most commonly related to portal hypertension from liver disease.