Spontaneous bacterial peritonitis
Formal Definition
An infection of ascitic fluid without an identifiable source of infection; occurs in patients with cirrhosis and ascites; diagnosed by ascitic fluid polymorphonuclear count >=250 cells/uL, with or without positive culture; treated with empiric IV antibiotics; requires secondary prophylaxis after recovery.
How It's Used on the Ward
SBP — infection of the fluid in the abdomen in a cirrhotic patient; often presents subtly (fever, abdominal pain, altered mental status) and needs a diagnostic tap to diagnose.
Example
"Cirrhotic patient with ascites, new confusion, temp 38.4C, HR 112. Paracentesis: PMN 480/uL (>250), protein 0.8 g/dL, albumin 0.6 g/dL (SAAG >1.1 = portal hypertension). Culture pending. Diagnosis: spontaneous bacterial peritonitis. Started ceftriaxone 2g IV daily. Albumin 1.5g/kg IV (100g for 70kg) to prevent circulatory dysfunction."
Clinical Context
Diagnosis: paracentesis is mandatory in any cirrhotic with ascites who is admitted to hospital, has symptoms, or has GI bleeding. PMN >=250/uL = SBP. SAAG (serum-ascites albumin gradient) >1.1 = portal hypertension-related ascites. Protein <1 g/dL + SAAG >1.1 = high SBP risk (give norfloxacin prophylaxis). Treatment: third-generation cephalosporin (ceftriaxone 2g daily for 5-7 days); fluoroquinolone if beta-lactam allergy. Albumin: 1.5g/kg on day 1, 1g/kg on day 3 in patients with cirrhosis and SBP — reduces mortality. Secondary prophylaxis: norfloxacin 400mg daily or trimethoprim-sulfamethoxazole once daily. Culture often negative (40%) — treat empirically if clinical suspicion.