5 Ascites

Causes and clinical importance

Ascites is abnormal fluid accumulation in the peritoneal cavity. In cirrhosis, portal hypertension and renal sodium and water retention are major contributors. Cardiac disease, malignancy, infection, and pancreatic disease can also cause ascites.

New or worsening ascites warrants evaluation for its cause and for complications, including spontaneous bacterial peritonitis (SBP), kidney injury, and hyponatremia.

Initial evaluation

When ascitic fluid is accessible, perform diagnostic paracentesis to help identify the cause and detect complications. Initial testing generally includes the ascitic-fluid cell count and differential, albumin, and total protein. Obtain a serum albumin at the same time to calculate the SAAG.

Culture is especially important when infection is suspected and should be collected before antibiotics. Fluid results help identify portal hypertension and detect SBP.

Prompt diagnostic paracentesis is recommended for patients with cirrhosis and ascites who are emergently hospitalized. It should also be performed when patients develop signs or laboratory findings suggestive of infection or clinical deterioration. SBP can occur without fever or abdominal pain.

Interpreting ascitic-fluid results

Calculate the serum–ascites albumin gradient (SAAG) by subtracting the ascitic-fluid albumin from the serum albumin:

For example, if serum albumin is $3.0\ \text{g/dL}$ and ascitic-fluid albumin is $1.5\ \text{g/dL}$, then:

A SAAG of $1.1\ \text{g/dL}$ or higher suggests that portal hypertension is contributing to the ascites. The SAAG helps classify the cause, but it should be interpreted alongside the history, examination, and other fluid results.

Interpreting ascitic-fluid protein

When the SAAG is high, ascitic-fluid total protein can help distinguish a cardiac contribution from cirrhotic ascites. A high SAAG with relatively high fluid protein, commonly greater than $2.5\ \text{g/dL}$, supports a cardiac cause; cirrhotic ascites more often has lower protein. This finding is a clue, not a stand-alone diagnosis.

Recognizing and treating infection

An ascitic-fluid polymorphonuclear leukocyte count of $250\ \text{cells/mm}^3$ or greater meets the commonly used diagnostic threshold for spontaneous bacterial peritonitis (SBP). Start empiric antibiotics promptly after obtaining appropriate cultures; do not wait for culture results. Consider an alternative intra-abdominal infection if the clinical picture suggests a focal source.

Infection may present as new confusion, worsening kidney function, or general deterioration rather than fever or localized pain. Assess promptly and investigate for infection, including diagnostic paracentesis when indicated.

Managing moderate ascites

For moderate ascites from cirrhosis, use moderate dietary sodium restriction of about $2\ \text{g}$ of sodium daily and diuretics, commonly spironolactone with or without a loop diuretic. Monitor weight, kidney function, and serum sodium and potassium, and adjust treatment according to response and adverse effects.

Fluid restriction is generally not needed unless clinically important hyponatremia is present. Avoid excessive dietary restriction that could worsen malnutrition.

Tense and refractory ascites

Large-volume paracentesis is an initial treatment for tense ascites causing substantial discomfort. When more than $5\ \text{L}$ is removed, albumin replacement is recommended to reduce the risk of post-paracentesis circulatory dysfunction. Guidance describes giving $6$–$8\ \text{g}$ of albumin per liter removed. Sodium restriction and diuretics may be used afterward as appropriate.

If ascites recurs despite appropriate sodium restriction and diuretic therapy, reassess adherence, precipitating factors, kidney function, and treatment tolerance. Repeated large-volume paracentesis is a key treatment for refractory ascites. Carefully selected patients may be considered for a transjugular intrahepatic portosystemic shunt (TIPS), which requires careful selection because it can increase the risk of hepatic encephalopathy and other complications.

Complications and broader care

When a patient with cirrhosis and ascites deteriorates, consider SBP or another infection, acute kidney injury including hepatorenal syndrome, hyponatremia, and hepatic encephalopathy. Investigate promptly, including for infection and with diagnostic paracentesis when indicated.

Clinically significant ascites is a decompensation event, so referral for liver-transplant evaluation should be considered.