Ascites pathophysiology

Ascites is the excess accumulation of fluid in the peritoneal cavity. The fluid can be defined as transudate or exudate. Amounts of up to 25 liters are fully possible. Roughly, transudates are a result of increased pressure in the portal vein (> 8 mmHg), such as cirrhosis; while exudates are actively secreted fluid due to inflammation or malignancy. The most useful measure is the difference between ascitic and serum albumin concentrations. A difference of less than 1.1 g/dl (10 g/L) implies an exudate. There is no genetic background for ascites. On gross pathology, clear to pale yellow fluid accumulation in peritoneal space are characteristic findings of ascites under normal condition, but it may be chylous, psudochylous, or bloody.

• Ascites is the excess accumulation of fluid in the peritoneal cavity. The fluid can be defined as a transudate or an exudate. Amounts of up to 25 liters are fully possible.^[1]
• Roughly, transudates are a result of increased pressure in the portal vein (> 8 mmHg), such as cirrhosis; while exudates are actively secreted fluid due to inflammation or malignancy.
• Exudates:
  • High protein
  • High lactate dehydrogenase (LDH)
  • Low pH (< 7.30)
  • Low glucose level
  • High white blood cells count
• Transudates:
  • Low protein (< 30 g/L)
  • Low lactate dehydrogenase (LDH)
  • High pH
  • Normal glucose
  • Fewer than 1 white blood cell per 1000 mm³

• The most useful measure is the difference between ascitic and serum albumin concentrations.
• A difference of less than 1.1 g/dl (10 g/L) implies an exudate.

• The main pathophysiology of ascites in cirrhotic patients consists of three interrelated mechanisms, include:^[2]
  • Portal hypertension
  • Vasodilation
  • Hyperaldosteronism
• There is a nitric oxide overload in cirrhotic patients from an unknown source. Therefore, they involved in hypovolemia secondary to the systemic vasodilation.^[3]
• The vasodilation induced by nitric oxide would trigger the stimulation of juxta-glumerular system to upregulate antidiuretic hormone (ADH) and sympathetic drive.^[4] Excess ADH causes water retention and volume overload.^[5]
• Despite the normal physiology of vessels, angiotensin would not cause vasoconstriction in cirrhotic patients and vasodilation becomes perpetuated.^[6]
• Portal hypertension leads to more production of lymph, to the extend of lymphatic system overload. Then, the lymphatic overflow will directed into to peritoneal cavity, forming ascites.^[7]

• Peritoneal malignancy produces some protein factors into the peritoneum, which may lead to osmotic drainage of water and fluid accumulation. Tuberculosis and other forms of ascites are induced through the same mechanism and osmotic fluid shift.^[8]
• Pancreatic and biliary ascites are induced through leakage of pancreatic secretions or bile into the peritoneal cavity, which may lead to inflammatory fluid shift and accumulation.

• There is no genetic background for ascites.
• Ascites syndrome, also called pulmonary hypertension, is in fact a genetic disorder in broilers and poultry.^[9]

Associated conditions with ascites are as following:^[10]

• Cirrhosis
• Heart failure
• Portal hypertension
• Kwashiorkor
• Viral hepatitis
• Pancreatic disease
• Biliary disease

• On gross pathology, clear to pale yellow fluid accumulation in peritoneal space are characteristic findings of ascites under normal condition.^[11]

• Chylous ascites gross pathology is milky presentation of ascites fluid, which is reflective of high amounts of chylomicrons.^[12]
• On gross pathology, milky appearance of ascitic fluid is characteristics of the followings:^[13]
  • Cirrhosis
  • Infections (parasitic and tuberculosis)
  • Malignancy
  • Congenital defects
  • Trauma
  • Inflammatory processes
  • Nephropathies
  • Cardiopathies

• Pseudochylous is the condition in which on gross pathology the ascitic fluid appearance is cloudy and/or turbid.
• The following conditions can lead to pseudochylous:^[14]
  • Bacterial infection
  • Peritonitis
  • Pancreatitis
  • Perforated bowel

• On gross pathology, bloody appearance of ascitic fluid is characteristics of the followings:^[15]
  • Benign or malignant tumors
  • Hemorrhagic pancreatitis
  • Perforated ulcer

• On microscopic histopathological analysis, characteristic findings of cirrhosis, as the most common cause of ascites, are based on Robbins definition (all three is needed for diagnosis):^[17]
  • Bridging fibrosis
  • Nodule formation
  • Disruption of the hepatic architecture

Template:WH Template:WS