Spontaneous Bacterial Peritonitis: Diagnosis and Management

Immediate Diagnostic Approach

Perform diagnostic paracentesis immediately in 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

Specific Triggers for Urgent Paracentesis

New or worsening abdominal pain or tenderness 1
Fever, hypothermia, chills, tachycardia, or tachypnea 1
New or worsening hepatic encephalopathy 1
Acute kidney injury or rising creatinine 1
Gastrointestinal bleeding (bacterial infection develops in 25-65% of these cases) 1
Hemodynamic instability or shock 1
Unexplained jaundice, metabolic acidosis, or peripheral leukocytosis 1

Critical Timing Consideration

In patients with septic shock, mortality increases by 10% for every hour's delay in initiating antibiotics. 1 Therefore, empirical antibiotics must be started immediately after paracentesis if infection is suspected, even before culture results return. 1

Diagnostic Criteria

Gold Standard Threshold

An ascitic fluid polymorphonuclear (PMN) count >250 cells/mm³ establishes the diagnosis of SBP and mandates immediate empirical antibiotic therapy. 1, 2 This threshold was deliberately chosen for its high sensitivity to avoid missing cases, as untreated SBP carries ~90% mortality. 1, 2

Essential Ascitic Fluid Tests (in order of priority)

Cell count with differential (must be completed within 4 hours) 2, 3
Bedside inoculation of ≥10 mL into aerobic and anaerobic blood culture bottles (increases culture sensitivity to >90%) 1, 2
Total protein concentration 1, 2, 3
Glucose and lactate dehydrogenase (LDH) (to differentiate secondary peritonitis) 2, 3
Gram stain (multiple organisms suggest secondary peritonitis) 2, 3

Additional Blood Work

Obtain blood cultures before starting antibiotics 1, 2
Leukocyte count with differential, skin examination, urine culture, and chest x-ray 1

Differentiating Secondary Bacterial Peritonitis from SBP

Secondary peritonitis requires surgical consultation and broader antibiotic coverage, so distinguishing it from SBP is critical. 1, 4

Runyon Criteria (≥2 of the following suggest secondary peritonitis):

Ascitic total protein ≥1 g/dL 2, 3
Ascitic LDH above serum upper limit of normal 2, 3
Ascitic glucose <50 mg/dL 2, 3

Additional Red Flags for Secondary Peritonitis:

Multiple organisms on Gram stain or culture (SBP is typically monomicrobial) 2, 3, 4
PMN count >1,000 cells/mm³ 2, 3
Localized abdominal symptoms or inadequate clinical response to antibiotics after 48 hours 1, 2
Ascitic CEA >5 ng/mL or alkaline phosphatase >240 U/L (suggests intestinal perforation) 3

If secondary peritonitis is suspected, obtain an abdominal CT scan immediately and consult surgery. 2, 3

Empirical Antibiotic Therapy

Start antibiotics immediately after paracentesis if PMN count >250 cells/mm³, without awaiting culture results. 1, 2

Community-Acquired SBP (First-Line)

Cefotaxime 2 g IV every 8-12 hours for 5 days (achieves 77-98% resolution rate; 5-day course is as effective as 10-day course) 1, 2, 3

Alternative: Ceftriaxone 2 g IV every 24 hours 1
Oral option for uncomplicated cases: Ofloxacin 400 mg PO twice daily (only if no prior quinolone exposure, no vomiting, no shock, and no grade II+ encephalopathy) 2, 3

Healthcare-Associated or Nosocomial SBP

Use broader-spectrum coverage due to rising multidrug-resistant organisms (MDROs), which represent 35% of infections in cirrhotic patients. 1, 5

Piperacillin-tazobactam 4.5 g IV every 6-8 hours 1, 2, 3
Meropenem 1 g IV every 8 hours (for critically ill patients or those with recent hospitalization) 1, 2, 3

Specific Contraindications

Avoid aminoglycosides (nephrotoxic in this population) 2, 3
Do not use quinolones if patient is already on quinolone prophylaxis, in areas with high quinolone resistance, or in nosocomial SBP 1, 2

Special Populations

For patients with SBP while on quinolone prophylaxis, use cefotaxime or amoxicillin-clavulanic acid. 2

For symptomatic patients with PMN <250 cells/mm³ but clear infection signs (fever >37.8°C, abdominal pain/tenderness), start empirical antibiotics while awaiting cultures. 3

Albumin Administration

All patients with SBP must receive intravenous albumin in addition to antibiotics, as this intervention reduces mortality from 29% to 10% and hepatorenal syndrome from 30% to 10%. 1, 2, 3

Dosing Protocol:

1.5 g/kg body weight within 6 hours of diagnosis 1, 2, 3
1.0 g/kg on day 3 1, 2, 3

The greatest benefit is observed in patients with serum bilirubin ≥4 mg/dL (68 µmol/L) and serum creatinine ≥1 mg/dL (88 µmol/L), but guidelines recommend albumin for all SBP cases. 2, 3

Monitoring Treatment Response

Repeat diagnostic paracentesis at 48 hours if clinical response is inadequate or if secondary peritonitis is suspected. 2, 3

Definition of Treatment Success:

PMN count decreases to <25% of pre-treatment value 1, 2, 3
Clinical improvement (reduced fever, abdominal pain, improved mental status) 1, 2

Definition of Treatment Failure:

PMN count fails to decrease by ≥25% or rises 1, 2, 3
Ongoing clinical deterioration at 48 hours 2, 3

If treatment failure occurs, suspect resistant organisms (modify antibiotics based on culture sensitivities or escalate empirically to broader-spectrum agents) or secondary peritonitis (obtain CT imaging and surgical consultation). 1, 2, 3

Secondary Prophylaxis (After SBP Episode)

All patients who recover from SBP require long-term oral antibiotics because recurrence risk is ~69% within one year. 2, 3

Regimen Options:

Norfloxacin 400 mg PO once daily 2, 3
Ciprofloxacin 500 mg PO once daily 2, 3
Trimethoprim-sulfamethoxazole 800/160 mg PO once daily 2, 3

All patients who recover from SBP should be assessed for liver transplantation eligibility. 2, 5

Primary Prophylaxis (High-Risk Situations)

Gastrointestinal Bleeding

Give prophylactic antibiotics to all cirrhotic patients with ascites who present with GI bleeding, as this reduces SBP incidence and re-bleeding rates. 2, 3

Ceftriaxone 1 g IV daily for 7 days (preferred, tailored to local resistance patterns) 1, 3
Alternative: Norfloxacin 400 mg PO twice daily for 7 days 3

Low Ascitic Fluid Protein

Consider primary prophylaxis in patients with ascitic fluid protein <1.5 g/dL without prior SBP. 2, 3

Prognosis

Despite appropriate therapy, in-hospital mortality for SBP remains ~20%, and one-year survival after an SBP hospitalization is approximately 34%. 2, 3 Early diagnosis and prompt treatment with antibiotics plus albumin significantly improve survival. 1, 2

Common Pitfalls and How to Avoid Them

Delaying paracentesis in asymptomatic cirrhotic patients: Up to one-third of SBP cases are completely asymptomatic, so perform paracentesis on all hospitalized cirrhotic patients with ascites. 1, 2
Waiting for culture results before starting antibiotics: Cultures are negative in up to 60% of SBP cases; the PMN count alone is sufficient to initiate therapy. 1, 2
Relying on leukocyte-esterase reagent strips: These lack sufficient diagnostic accuracy and are not recommended for routine use. 1, 3
Treating culture-negative neutrocytic ascites (PMN >250/mm³ with negative culture) differently from culture-positive SBP: Both have identical morbidity and mortality and require the same treatment. 2, 3
Treating bacterascites (positive culture but PMN <250/mm³) without clinical judgment: If symptomatic, treat as SBP; if asymptomatic, repeat paracentesis as 38% will progress to frank SBP. 2
Placing a chest tube for spontaneous bacterial empyema (pleural fluid PMN >250/mm³): Despite the term "empyema," a chest tube should not be placed; treat with antibiotics as for SBP. 1

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