Ascites is abnormal free fluid floating in the abdomen (i.e. in the Peritoneal Cavity; see Diagram – The Gastrointestinal System). The main cause is Cirrhosis of the liver, because scars there block veins passing through the organ, slowing blood flow, so fluid leaks out. The condition is also called “Portal Hypertension,” meaning too much pressure build-up in the liver’s portal vein (nothing to do with the common Hypertension in arteries, that causes heart attacks and strokes). Other causes of ascites include severe heart failure (blood backs up if the heart can’t pump efficiently), and abdominal cancers.
Ascites itself may be uncomfortable but isn’t so dangerous, the main complications come from whatever disease causes it. The one risk of the ascites is if the fluid becomes infected, causing Peritonitis. Most Peritonitis is due to other conditions like a ruptured bowel; then it’s severe and obvious (high fever, terrible pain), causing Sepsis (& death if untreated). But a lesser form happens with ascites, called “Subacute Bacterial Peritonitis” (SBP), with much more subtle signs and symptoms. If undiagnosed, it will eventually evolve into full-blown disease. We have to think of SBP whenever a person with known cirrhosis develops new abdominal pain or fever, even if mild. If we find ascitic fluid, we examine it for infection; if no ascites, then no SBP.
Low levels of ascites can only be detected by ultrasound or CT scan. A main clue for clinicians is new weight gain. Moderate ascites can often be found on physical exam, by a clever technique called “shifting dullness.” Massive ascites is obvious by just looking (there’s a mnemonic for the different causes of a distended bulging abdomen: “the 6 F’s“; can you guess the words?. I’ve seen patients with 90 pounds of weight gain, which equals 40 quarts (10 gallons) of unwanted fluid!
We can examine ascitic fluid by “tapping it” – aspirating a specimen by needle and syringe (called paracentesis). This can provide great relief, but the main reason for doing so is to look for infection or cancer. Unfortunately, if we just remove fluid for relief, it rapidly builds right back up. Various medications can help prevent accumulation, but the only effective therapy is by treating the underlying disease (which often may be impossible if, for example, liver damage is permanent).