Ascites

Ascites is the buildup of fluid in the peritoneal cavity. The most accepted explanation is the splanchnic vasodilation model.

In cirrhosis, excess nitric oxide and other vasodilators cause dilation of the splanchnic arteries. This lowers the effective circulating blood volume, despite an increase in total body fluid.

The body responds by activating the renin–angiotensin–aldosterone system and antidiuretic hormone. These responses promote sodium and water retention.

Plasma volume expansion then raises sinusoidal pressure in the liver. This pressure forces lymph to leak into the peritoneal cavity, resulting in the formation of ascites, also known as ascitic fluid.

As fluid continues to accumulate, the adequate circulating volume continues to fall further. This leads to the underfill stage, which triggers even stronger fluid retention.

Besides this mechanism, systemic inflammation, intestinal and mesenteric changes, malignancies, and cardiac or renal dysfunction can also worsen ascites.