Spontaneous Bacterial Empyema (SBEM)


🔍 Definition:

SBEM is infection of a pre-existing hepatic hydrothorax (pleural effusion in cirrhotic patients) without pneumonia. It is analogous to Spontaneous Bacterial Peritonitis (SBP) in the pleural space.

Occurs in the absence of pneumonia, unlike parapneumonic effusion or true empyema.


📊 Epidemiology:

  • Occurs in ~13–16% of patients with hepatic hydrothorax.
  • Mortality: 20–38%, higher in ICU.
  • Often underdiagnosed due to subtle signs and lack of suspicion.


🔬 Pathophysiology:

Step

Explanation

1. Portal hypertension

Causes hepatic hydrothorax due to fluid movement through diaphragmatic defects.

2. Immune dysfunction

Cirrhosis leads to decreased opsonization, complement, and PMN function.

3. Bacterial translocation

Gut flora translocates → bloodstream → pleural space.

4. Secondary infection

The normally sterile hydrothorax fluid becomes infected.



🧪 Causative Organisms:

  • Gram-negative bacilli:
    • E. coli (most common)
    • Klebsiella pneumoniae
  • Gram-positive cocci:
    • Streptococcus pneumoniae
    • Enterococcus
    • Staphylococcus aureus

Anaerobes are rare unless secondary to GI perforation.


🧠 Clinical Features:

  • Often asymptomatic or subtle signs
  • Fever, chills
  • Pleuritic chest pain
  • Worsening dyspnea
  • Altered sensorium, confusion (hepatic encephalopathy)
  • No features of pneumonia on CXR


🧪 Diagnosis:

A. Imaging:

  • Chest X-ray: Pleural effusion (usually on right side); no lung consolidation
  • CT chest: Rules out pneumonia or empyema; often just shows hydrothorax

B. Thoracentesis – Diagnostic Criteria

  1. Positive pleural fluid culture with PMN ≥250 cells/mm³
  2. OR PMN >500 cells/mm³ even if culture is negative, and no pneumonia on imaging

pH, glucose, LDH often normal or only mildly deranged (fluid remains transudative)

Parameter

SBEM

PMN count

≥250 (positive culture) or >500 (culture-negative)

Protein

Low (transudate)

Glucose

Normal to mildly reduced

pH

>7.2

Culture

Often positive

ADA

Normal

CXR/CT

No parenchymal infiltrate



❗ Differentiating SBEM from Empyema

Feature

SBEM

Empyema

Underlying disease

Cirrhosis with hepatic hydrothorax

Pneumonia or infection of lung

Pleural fluid

Transudate

Exudate

Pleural fluid pH

>7.2

<7.2

Glucose

Normal to mildly low

<40 mg/dL

Protein

Low

High

LDH

Normal or slightly high

High

Chest imaging

No pneumonia

Pneumonic infiltrates seen



 Management:

A. Empirical Antibiotics:

Same as SBP treatment (3rd-gen cephalosporin ± albumin)

Drug

Dose

Cefotaxime

2 g IV q8h (preferred)

OR Ceftriaxone

1–2 g IV q24h

If hospital-acquired/MDR risk

Piperacillin-tazobactam, Meropenem ± Vancomycin


  • Duration: 7–10 days


B. Albumin Infusion

(Same as SBP)

  • Indications: Creatinine >1 or bilirubin >4
  • Dose: 1.5 g/kg on day 1, then 1 g/kg on day 3

Prevents renal dysfunction and improves survival.


C. Chest Tube Drainage:

  • NOT routinely recommended
  • Indicated only if:
    • Gross pus
    • Loculated empyema
    • Respiratory distress due to massive effusion

Risks of fluid loss, protein depletion, and secondary infection are high in cirrhotics with routine chest tubes.


D. Definitive Treatment:

  • TIPS (Transjugular Intrahepatic Portosystemic Shunt) – for refractory hydrothorax/SBEM
  • Liver transplantation – definitive cure


⚠️ Complications:

  • Sepsis, multiorgan failure
  • Recurrence of SBEM
  • Worsening hepatic encephalopathy
  • Hepatorenal syndrome (HRS)
  • Death (up to 40% if not recognized early)