A 52-year-old woman with known cirrhosis and portal hypertension presents with acute-onset severe abdominal pain, fever (38.5°C), and abdominal distension. Diagnostic paracentesis reveals ascitic fluid with a serum-ascites albumin gradient (SAAG) of 1.8 g/dL, WBC 450/μL (80% neutrophils), and negative bacterial culture. What is the most appropriate immediate next step in management?

Explanation

## Spontaneous Bacterial Peritonitis (SBP) in Cirrhosis **Key Point:** SBP is a life-threatening complication of cirrhosis with portal hypertension. Diagnosis is clinical + biochemical; antibiotics must be started immediately—delays increase mortality. ### Diagnostic Criteria for SBP | Criterion | Value | Interpretation | |-----------|-------|----------------| | SAAG | ≥1.1 g/dL | Indicates portal hypertension | | Ascitic PMN count | >250 cells/μL | Diagnostic threshold for SBP | | Bacterial culture | Negative in ~60% | Culture-negative SBP is common | | Gram stain | Usually negative | Low yield; do not wait for results | **Clinical Pearl:** This patient has **culture-negative SBP** (CNBP)—ascitic PMN >250 cells/μL with negative culture. This occurs in ~60% of SBP cases due to low bacterial inoculum and is treated identically to culture-positive SBP. ### Pathophysiology ```mermaid flowchart TD A[Cirrhosis + Portal Hypertension]:::outcome --> B[Impaired opsonic activity<br/>Low complement, IgG]:::outcome A --> C[Bacterial translocation<br/>from gut]:::outcome B --> D[Seeding of ascitic fluid]:::outcome C --> D D --> E{Ascitic PMN >250?}:::decision E -->|Yes| F[SBP diagnosed]:::outcome E -->|No| G[Observe]:::action F --> H[Start antibiotics<br/>IMMEDIATELY]:::urgent H --> I[Ceftriaxone 1g IV Q12H<br/>or Cefotaxime]:::action I --> J[Albumin infusion<br/>1.5 g/kg at diagnosis<br/>+ 1 g/kg on day 3]:::action J --> K[Repeat paracentesis<br/>at 48 hours]:::action K --> L{PMN improved?}:::decision L -->|Yes| M[Continue antibiotics<br/>7-10 days]:::action L -->|No| N[Consider secondary peritonitis<br/>Imaging + surgical evaluation]:::urgent ``` ### Management Principles 1. **Immediate Antibiotic Initiation** - Do NOT wait for culture results - Do NOT wait for imaging - Ceftriaxone 1 g IV Q12H or cefotaxime 2 g IV Q4–6H - Mortality increases significantly with each hour of delay 2. **Albumin Infusion** - 1.5 g/kg at diagnosis, then 1 g/kg on day 3 - Reduces renal failure and mortality by ~50% - Mechanism: expands plasma volume, improves renal perfusion 3. **Imaging (After Antibiotics Started)** - CT abdomen/pelvis to exclude secondary peritonitis (perforation, abscess) - Secondary peritonitis: multiple organisms, high lactate, imaging findings - If secondary peritonitis suspected → surgical evaluation 4. **Repeat Paracentesis at 48 Hours** - Assess response: PMN should decrease by ≥30% - Failure to improve → consider secondary peritonitis or resistant organisms **High-Yield:** The **SAAG >1.1 g/dL** in this patient confirms portal hypertension as the cause of ascites. The ascitic PMN >250 cells/μL (even with negative culture) is diagnostic of SBP and mandates immediate antibiotic therapy. **Mnemonic:** **ABCD** for SBP management: - **A**ntibiotics immediately (ceftriaxone) - **B**lood cultures before antibiotics (if possible, but do not delay) - **C**linical assessment for secondary peritonitis - **D**iagnostic imaging (CT) after antibiotics started ### Why This Approach Is Correct SBP is a medical emergency with mortality ~15–20% even with treatment. Delaying antibiotics for culture results, imaging, or repeat paracentesis increases mortality. The combination of clinical presentation (fever, pain, distension), SAAG >1.1, and ascitic PMN >250 is sufficient for diagnosis. Imaging is important to exclude secondary peritonitis (which requires surgery), but must not delay antibiotic initiation.