What are the diagnostic criteria and management strategies for a patient suspected of having spontaneous bacterial peritonitis (SBP)?

Spontaneous Bacterial Peritonitis: Diagnostics and Management

Diagnostic Approach

Perform diagnostic paracentesis immediately in all hospitalized cirrhotic patients with ascites, even without symptoms, and diagnose SBP when ascitic fluid polymorphonuclear (PMN) count exceeds 250/mm³. 1

When to Perform Diagnostic Paracentesis

• At hospital admission: All cirrhotic patients with ascites require diagnostic paracentesis upon admission, as 16% of SBP cases are completely asymptomatic 1
• Clinical triggers: Perform urgent paracentesis in patients with fever, abdominal pain or tenderness, altered mental status, hepatic encephalopathy, gastrointestinal bleeding, shock, worsening liver or renal function, or any signs of systemic inflammation 2, 1
• Timing is critical: Each hour of delay in paracentesis increases in-hospital mortality by 3.3%, and delayed paracentesis (>12 hours) is associated with 2.7-fold increased mortality risk 3

Diagnostic Criteria

• PMN count >250/mm³ confirms SBP diagnosis regardless of culture results 1, 4
• The 250/mm³ threshold is deliberately chosen because the greater clinical risk lies with underdiagnosing SBP rather than overdiagnosing it 1
• Obtain at least 10 mL of ascitic fluid and inoculate blood culture bottles at bedside before starting antibiotics to increase culture sensitivity to >90% 1, 5
• Simultaneously obtain blood cultures before antibiotic initiation 2, 4

Special Diagnostic Scenarios

Bacterascites (positive culture but PMN <250/mm³):

• If symptomatic with signs of systemic inflammation: treat as SBP 2
• If asymptomatic: repeat paracentesis, as 38% will progress to frank SBP 1
• Treat if repeat PMN count >250/mm³; otherwise follow closely 2

Culture-negative neutrocytic ascites (PMN >250/mm³ with negative culture):

• Treat identically to culture-positive SBP, as both have similar morbidity and mortality 1

Secondary bacterial peritonitis:

• Suspect when localized abdominal symptoms, multiple organisms on culture, very high PMN count, high ascitic protein, or inadequate response to therapy 2
• Perform CT scanning for suspected secondary peritonitis 2, 5

Contraindications to Paracentesis

• Coagulopathy is NOT a contraindication despite prolonged prothrombin time in most cirrhotic patients 6
• Consider platelet transfusion only if platelets <40,000-50,000/μL 6
• Use ultrasound guidance to optimize the procedure 7

Management Strategy

Initiate empirical antibiotics immediately upon diagnosis without waiting for culture results, using third-generation cephalosporin plus intravenous albumin. 1, 4

First-Line Antibiotic Therapy

Community-acquired SBP:

• Cefotaxime 2g IV every 8-12 hours for 5 days (most extensively studied with 77-98% resolution rates) 1, 4
• Alternative: Ceftriaxone 2g IV daily 5
• Oral option for uncomplicated cases: Ofloxacin 400mg twice daily 1
• Five-day therapy is as effective as 10-day treatment 1, 4

Nosocomial or healthcare-associated SBP:

• Use broad-spectrum antibiotics: carbapenem or piperacillin-tazobactam based on local resistance patterns 5, 6, 7
• This is critical as gram-positive bacteria and multidrug-resistant organisms are increasing 8, 7

Patients on quinolone prophylaxis:

• Do NOT use quinolones for treatment 1
• Use cefotaxime or amoxicillin-clavulanic acid instead 1

Albumin Therapy: Essential Component

Administer IV albumin 1.5 g/kg body weight within 6 hours of diagnosis, followed by 1.0 g/kg on day 3. 1, 4

• This regimen reduces mortality from 29% to 10% and decreases type 1 hepatorenal syndrome from 30% to 10% 1
• Particularly critical in patients with creatinine ≥1.0 mg/dL or bilirubin ≥5 mg/dL 5
• Albumin therapy significantly reduces risk of hepatorenal syndrome and mortality 1, 4

Monitoring Treatment Response

Perform repeat paracentesis at 48 hours to assess treatment efficacy. 4, 5

• Treatment success: PMN count decreases to <25% of pre-treatment value with clinical improvement 1, 4
• Treatment failure: PMN count fails to decrease by at least 25% or worsening clinical signs 4, 5

Management of Treatment Failure

If PMN count fails to decrease by ≥25% at 48 hours:

• Consider resistant bacteria requiring antibiotic modification based on culture sensitivities 1
• Empirically escalate to broader-spectrum agents (carbapenem or piperacillin-tazobactam) 1
• Perform CT imaging to exclude secondary bacterial peritonitis requiring surgical consultation 1, 5

Critical Pitfalls to Avoid

• Never delay antibiotics waiting for culture results—the PMN count alone is sufficient to initiate therapy 1
• Never delay paracentesis due to coagulopathy concerns—routine transfusion is not recommended 7
• Never use quinolones in patients already on quinolone prophylaxis, in areas with high quinolone resistance, or in nosocomial SBP 1
• Never omit albumin therapy—it is essential and significantly improves survival 1, 4
• Never skip the 48-hour follow-up paracentesis—it identifies treatment failures requiring intervention 4, 5

Prognosis

• SBP carries approximately 20% hospital mortality despite infection resolution 1, 4
• Early appropriate antibiotic treatment combined with albumin therapy significantly improves survival 1, 4
• Delaying antibiotic therapy increases mortality by 10% for every hour's delay in cirrhotic patients with septic shock 1