Spontaneous Bacterial Peritonitis (SBP)

A 56 year old male with a history of alcohol-related liver cirrhosis presents with fever, diffuse abdominal pain, worsening abdominal distension, and confusion for 2 days. On examination, temperature is 38.5°C, pulse is 108/min, and abdomen is distended with shifting dullness and diffuse tenderness. Laboratory investigations reveal leukocytosis and elevated serum bilirubin. Diagnostic paracentesis demonstrates cloudy ascitic fluid with a polymorphonuclear leukocyte (PMN) count of 620 cells/mm³. Diagnosis?

Diagnosis is spontaneous bacterial peritonitis (SBP).

1. Definition

Spontaneous bacterial peritonitis is infection of ascitic fluid in the absence of an intra-abdominal surgically treatable source of infection.

2. Etiology

Common Causative Organisms

1. Escherichia coli (most common)
2. Klebsiella species
3. Streptococcus pneumoniae
4. Other enteric gram-negative organisms

3. Pathophysiology

1. Cirrhosis leads to portal hypertension and ascites formation
2. Impaired immune function predisposes to infection
3. Increased intestinal permeability allows bacterial translocation from the gut
4. Bacteria seed ascitic fluid causing infection
5. Systemic inflammatory response may lead to renal dysfunction and sepsis

4. Risk Factors

1. Liver cirrhosis with ascites
2. Low ascitic fluid protein concentration (<1.5 g/dL)
3. Previous SBP episode
4. Gastrointestinal bleeding
5. Advanced liver disease
6. Hospitalization

5. Clinical Features

1. Fever
2. Diffuse abdominal pain or tenderness
3. Increasing ascites
4. Altered mental status
5. Hypotension
6. Ileus
7. Worsening hepatic encephalopathy

Some patients may present with subtle or minimal symptoms

6. Diagnosis

6.1 Diagnostic Paracentesis

Diagnostic paracentesis should be performed in all hospitalized cirrhotic patients with ascites, especially before antibiotic administration

6.2 Diagnostic Criteria

1. Ascitic fluid PMN count ≥250 cells/mm³
2. Positive ascitic fluid culture supports diagnosis but is not required

6.3 Ascitic Fluid Analysis

1. Cell count with differential
2. Gram stain and culture
3. Albumin and total protein
4. Serum-ascites albumin gradient (SAAG) if needed

6.4 Laboratory Findings

1. Leukocytosis
2. Elevated inflammatory markers
3. Worsening liver function tests
4. Renal dysfunction may occur

7. Secondary Bacterial Peritonitis

Consider secondary bacterial peritonitis if there is:

1. Polymicrobial culture
2. Very high neutrophil count
3. Poor response to antibiotics
4. Low ascitic glucose
5. High ascitic protein
6. Elevated ascitic LDH
7. Imaging evidence of intra-abdominal pathology

Secondary bacterial peritonitis requires urgent evaluation for a surgically treatable source

8. Differential Diagnosis

1. Secondary bacterial peritonitis
2. Tuberculous peritonitis
3. Pancreatic ascites
4. Peritoneal carcinomatosis

9. Management

9.1 Antibiotic Therapy

Third-Generation Cephalosporins

1. Cefotaxime
2. Ceftriaxone

These are first-line therapies for community-acquired SBP

Nosocomial SBP may require broader-spectrum antibiotic coverage

9.2 Albumin Infusion

1. Reduces risk of hepatorenal syndrome and mortality
2. Recommended particularly in patients with renal dysfunction, elevated bilirubin, or advanced disease

Typical regimen:

• Day 1: 1.5 g/kg
• Day 3: 1 g/kg

9.3 Secondary Prophylaxis

Long-term antibiotic prophylaxis is recommended after an episode of SBP

Options include:

1. Ciprofloxacin
2. Trimethoprim-sulfamethoxazole

9.4 Primary Prophylaxis

Consider prophylactic antibiotics in high-risk patients with:

1. Low ascitic fluid protein concentration (<1.5 g/dL)
2. Advanced cirrhosis
3. Gastrointestinal bleeding

10. Complications

1. Sepsis
2. Hepatorenal syndrome
3. Hepatic encephalopathy
4. Recurrent SBP
5. Multiorgan failure

11. Prognosis

1. SBP is associated with high mortality if untreated
2. Early diagnosis and treatment improve outcomes
3. Recurrence is common without prophylaxis

12. Key Clinical Insight

Cirrhotic patient with ascites presenting with fever, abdominal pain, encephalopathy, renal dysfunction, or unexplained clinical deterioration should be presumed to have spontaneous bacterial peritonitis until proven otherwise

13. Key Exam Points

1. SBP is infection of ascitic fluid without a surgically treatable source
2. Most common organism is Escherichia coli
3. Diagnostic criterion: ascitic fluid PMN count ≥250 cells/mm³
4. Positive culture is not required for diagnosis
5. Diagnostic paracentesis should be performed in all hospitalized cirrhotic patients with ascites
6. Third-generation cephalosporins are first-line therapy
7. Albumin infusion reduces risk of hepatorenal syndrome and mortality
8. Ciprofloxacin or TMP-SMX may be used for prophylaxis
9. Low ascitic protein is a major risk factor
10. Secondary bacterial peritonitis must be excluded if response to therapy is poor