How do I diagnose and manage spontaneous bacterial peritonitis in an adult cirrhotic patient with ascites presenting with fever, abdominal pain, altered mental status, or renal dysfunction?

Diagnosis and Management of Spontaneous Bacterial Peritonitis

Perform diagnostic paracentesis immediately in any cirrhotic patient with ascites upon hospital admission or when infection is suspected, and start intravenous cefotaxime 2 g every 8 hours plus albumin 1.5 g/kg if the ascitic fluid polymorphonuclear count exceeds 250 cells/mm³.

When to Perform Diagnostic Paracentesis

Paracentesis is mandatory in the following situations:

• Every cirrhotic patient with ascites upon hospital admission, regardless of symptoms, because approximately 10-30% have SBP at presentation and up to one-third are completely asymptomatic 1, 2
• Fever or systemic inflammatory signs including chills, tachycardia, tachypnea, or hypothermia 2, 3
• Abdominal pain or tenderness of any severity 1, 2
• New or worsening hepatic encephalopathy without obvious precipitating factors 1, 2
• Deteriorating renal function with rising creatinine 1, 2
• Gastrointestinal bleeding, as bacterial infection develops in 25-65% of these cases 1, 2
• Unexplained peripheral leukocytosis, metabolic acidosis, or hemodynamic instability 1, 2

Critical pitfall: Delaying paracentesis in asymptomatic patients leads to missed diagnoses, as one-third of SBP cases lack symptoms 2, 3. The mortality of untreated SBP approaches 90% but drops to approximately 20% with early treatment 1, 3.

Diagnostic Criteria

The gold standard for SBP diagnosis is an ascitic fluid polymorphonuclear (PMN) count >250 cells/mm³ 1, 2. This threshold provides optimal sensitivity, though a cutoff of >500 cells/mm³ increases specificity at the cost of sensitivity 1.

Essential Ascitic Fluid Tests (in order of priority):

1. Cell count with differential – the most critical test, completed in <4 hours 2
2. Gram stain and culture – inoculate into blood culture bottles at bedside to improve yield 1
3. Total protein concentration 1, 2
4. Glucose and lactate dehydrogenase (LDH) to differentiate secondary peritonitis 1, 2

Do not rely on leukocyte esterase reagent strips – they lack sufficient diagnostic accuracy for routine use 2.

Variants of SBP:

• Classic SBP: PMN ≥250 cells/mm³ with positive culture (single organism) 4
• Culture-negative neutrocytic ascites (CNNA): PMN ≥250 cells/mm³ with negative culture despite proper technique; accounts for ~40% of cases and must be treated identically to culture-positive SBP 4
• Monomicrobial non-neutrocytic bacterascites (MNB): Positive culture with PMN <250 cells/mm³; if asymptomatic, repeat paracentesis to confirm clearance; if symptomatic, treat immediately 4

Differentiating Secondary Bacterial Peritonitis

Secondary peritonitis requires surgical intervention, not just antibiotics. Suspect it when:

• Multiple organisms are identified on Gram stain or culture 1, 2, 4
• At least two of the following (Runyon criteria): ascitic total protein ≥1 g/dL, LDH above serum upper limit of normal, glucose <50 mg/dL 1, 2
• PMN count >1,000 cells/mm³ 1, 4
• Inadequate clinical response to appropriate antibiotics after 48 hours 1, 2, 4
• Localized abdominal signs such as guarding or rebound tenderness 4
• Elevated ascitic CEA >5 ng/mL or alkaline phosphatase >240 U/L, suggesting intestinal perforation 4

When secondary peritonitis is suspected, obtain an urgent abdominal CT scan and involve surgery immediately 2, 4.

Empirical Antibiotic Therapy

Start antibiotics immediately after paracentesis if PMN >250 cells/mm³, without awaiting culture results 1, 2, 3. Waiting for cultures is harmful, as up to 60% of SBP cases are culture-negative 2.

Community-Acquired SBP:

First-line: Cefotaxime 2 g IV every 8 hours (or every 12 hours, as both dosing regimens are equally effective) 1, 2, 3

• Achieves 77-98% resolution rates 2
• 5-day course is as effective as 10-day course 2

Alternatives with comparable efficacy:

• Amoxicillin-clavulanic acid (IV then oral) 2
• Ciprofloxacin (7 days IV or 2 days IV followed by 5 days oral) 2
• Oral ofloxacin 400 mg twice daily for selected inpatients without prior quinolone exposure, vomiting, shock, or grade II+ encephalopathy 1, 2

Healthcare-Associated or Nosocomial SBP:

Use broader-spectrum coverage due to rising multidrug resistance 2, 3:

• Piperacillin-tazobactam or carbapenem (e.g., meropenem) 2, 3, 5
• Tailor therapy based on local resistance patterns 3

Avoid aminoglycosides due to nephrotoxicity in this high-risk population 1, 3.

Symptomatic Patients with PMN <250 cells/mm³:

If fever >37.8°C, abdominal pain, or tenderness are present, start empiric antibiotics while awaiting culture results 2, 3.

Albumin Administration

All patients with SBP should receive intravenous albumin in addition to antibiotics 1, 2:

• Dosing: 1.5 g/kg at diagnosis (within 6 hours) and 1.0 g/kg on day 3 1, 2, 3
• Benefits: Reduces hepatorenal syndrome from 30% to 10% and lowers 30-day mortality from 29% to 10% compared to antibiotics alone 2
• Greatest benefit in patients with serum bilirubin ≥4 mg/dL (≥68 µmol/L) and creatinine ≥1 mg/dL (≥88 µmol/L), though guidelines recommend albumin for all SBP cases 2

Avoid nephrotoxic agents (NSAIDs, aminoglycosides, contrast) and resuscitate hypotension with IV fluids and albumin 3.

Monitoring and Follow-Up

Repeat paracentesis at 48 hours if clinical response is inadequate or if secondary peritonitis is suspected 1, 2, 3. This verifies decreasing PMN count and guides further management.

Prophylaxis Strategies

Secondary Prophylaxis (After an SBP Episode):

Long-term oral antibiotics are mandatory because recurrence risk is ~69% within one year 1, 2:

• Norfloxacin 400 mg once daily 1, 2
• Ciprofloxacin 500 mg once daily 2
• Trimethoprim-sulfamethoxazole 800/160 mg once daily 1, 2

Primary Prophylaxis:

• Gastrointestinal bleeding: Give ceftriaxone 1 g IV daily for 7 days (or norfloxacin 400 mg twice daily for 7 days) to prevent SBP and reduce re-bleeding 1, 2
• Low ascitic fluid protein (<1.5 g/dL) without prior SBP: Consider primary prophylaxis 1, 2

Special Consideration: Spontaneous Bacterial Empyema

Spontaneous bacterial empyema (SBE) is infection of pre-existing hepatic hydrothorax in the absence of pneumonia 4:

• Diagnostic criteria: Pleural fluid neutrophils >250 cells/mm³ with positive culture or >500 cells/mm³ with negative culture 4
• Culture yield: Using blood culture bottles achieves ~75% positivity 4
• Mortality: ~38%, occurring in ~16% of cirrhotic patients with hepatic hydrothorax 4
• Treatment: Same as SBP (cefotaxime + albumin) 4

Common Pitfalls to Avoid

• Delaying paracentesis in asymptomatic cirrhotic patients leads to missed diagnoses 2, 3
• Waiting for culture results before starting antibiotics is harmful 2, 3
• Assuming surgical pathology without evidence; most cirrhotic patients with peritonitis have SBP (medical), not secondary peritonitis (surgical) 3
• Using leukocyte esterase strips for diagnosis due to poor accuracy 2
• Withholding paracentesis due to coagulopathy; prolonged PT/INR is not a contraindication, though consider platelet transfusion if <40,000-50,000/μL 6