Pleural Effusion:  

Definition:
Pleural effusion is the abnormal accumulation of fluid in the pleural space, the potential cavity between the visceral and parietal pleura. Normally, a small amount of pleural fluid (~10–20 mL) lubricates the pleural surfaces, facilitating smooth lung expansion during respiration. Pathological accumulation can impair lung mechanics and gas exchange, leading to respiratory symptoms.

Pathophysiology:
Pleural fluid homeostasis is maintained by a balance of hydrostatic pressure, oncotic pressure, and lymphatic drainage. Disruption of these forces results in fluid accumulation:

• Transudative effusions: Occur due to systemic imbalances in hydrostatic or oncotic pressures without pleural membrane injury. Commonly seen in:

  • Congestive heart failure (↑ hydrostatic pressure)

  • Cirrhosis (hepatic hydrothorax, ↓ oncotic pressure)

  • Nephrotic syndrome (protein loss)

  • Chronic kidney disease with sodium and water retention

• Exudative effusions: Occur due to increased pleural capillary permeability or impaired lymphatic drainage from local pleural pathology. Causes include:

  • Infection: bacterial (pneumonia, empyema), tuberculosis

  • Malignancy: primary (mesothelioma) or metastatic (lung, breast, ovarian cancers)

  • Inflammatory conditions: SLE, rheumatoid arthritis, vasculitis

  • Pulmonary embolism with infarction

  • Trauma: hemothorax, chylothorax, iatrogenic

Transudate vs. Exudate:
Laboratory differentiation uses Light’s criteria:

Parameter	Transudate	Exudate
Pleural fluid protein / serum protein	≤0.5	>0.5
Pleural fluid LDH / serum LDH	≤0.6	>0.6
Pleural fluid LDH	<2/3 upper limit of normal serum LDH	>2/3 upper limit

Adjunctive tests: pleural fluid cholesterol, glucose, pH, cell count, cytology, and microbiology further help identify etiology.

---

Clinical Features

Symptoms:

• Small effusions (<300 mL) are often asymptomatic.

• Dyspnea, especially on exertion

• Pleuritic chest pain (sharp, worsens with inspiration)

• Dry, nonproductive cough

• Systemic symptoms depending on the underlying cause (fever in infection, cachexia in malignancy, orthopnea in CHF)

Physical Examination:

• Inspection: decreased chest expansion on affected side

• Palpation: reduced tactile fremitus

• Percussion: dullness over fluid

• Auscultation: decreased or absent breath sounds; pleural friction rub if inflamed

---

Diagnostics

Imaging:

• Chest X-ray: First-line. Lateral decubitus views detect as little as 5 mL fluid. Findings include:

  • Blunting of costophrenic angles

    
    
    

  • Homogeneous opacity with meniscus sign

    
    
    

  • Large effusions: mediastinal shift, complete lung opacity

    
    
    

• Thoracic Ultrasound: Sensitive for fluid ≥20 mL. Detects septations, pleural thickening, and guides thoracentesis.

  
  
  

• Chest CT: Gold standard for small effusions. IV contrast may reveal malignancy; CT angiography identifies vascular causes.

  
  
  

Thoracentesis:

• Diagnostic and therapeutic.

• Indications: new or atypical effusions, symptomatic relief.

• Fluid analysis guides differentiation between transudate and exudate and identifies specific etiology.

Pleural Fluid Analysis Highlights:

• Transudate: Clear, low protein, low LDH, low WBC count, normal pH/glucose.

• Exudate: Cloudy/purulent, high protein, high LDH, elevated WBC count.

• Low glucose (<60 mg/dL): Seen in malignancy, empyema, rheumatoid pleuritis, tuberculosis (MEAT).

• Bloody fluid: Suggests malignancy or hemothorax.

• Chylous fluid: Milky, high triglycerides (>110 mg/dL), lymphocyte predominance.

• Pseudochylous fluid: Chronic, cholesterol-rich (>200 mg/dL), low triglycerides.

---

Special Subtypes

1. Parapneumonic Effusion:

   • Exudative fluid secondary to pneumonia.

   • Uncomplicated: sterile, resolves with antibiotics.

   • Complicated: bacterial invasion, pH <7.2, low glucose, high LDH, requires drainage.

2. Empyema:

   • Pus accumulation, often stage-wise: exudative → fibrinopurulent → organizing.

   • Diagnosis: imaging (CT split-pleura sign), purulent fluid, culture positive.

   • Treatment: antibiotics + drainage (thoracostomy, VATS if needed).

3. Nontraumatic Hemothorax:

   • Spontaneous accumulation of blood (RBC count >5,000/µL).

   • Causes: pneumothorax, malignancy, coagulopathy.

   • Requires drainage to prevent trapped lung/empyema.

4. Malignant Pleural Effusion:

   • Exudative with malignant cells.

   • Symptoms: dyspnea, cachexia, hemoptysis.

   • Treatment: thoracentesis, indwelling catheter, pleurodesis, treat primary malignancy.

5. Chylothorax:

   • Lymphatic fluid in pleural space, causes: trauma, malignancy, congenital anomalies.

   • Conservative: diet, TPN, octreotide.

   • Surgical: thoracic duct repair/ligation, pleurodesis.

6. Pseudochylothorax:

   • Chronic inflammatory effusion, cholesterol-rich.

   • Management mirrors chylothorax.

---

Management

Immediate:

• Respiratory support for unstable patients

• Urgent thoracentesis if respiratory compromise

General Principles:

• Treat the underlying cause (CHF, infection, malignancy, autoimmune disease)

• Therapeutic thoracentesis for large, symptomatic, or complicated effusions

• Limit fluid removal to 1–1.5 L per session to prevent reexpansion pulmonary edema

Recurrent or Malignant Effusions:

• Indwelling pleural catheter for repeated drainage

• Chemical pleurodesis (talc, doxycycline) or surgical pleurodesis

• Surgical interventions (VATS, decortication) for loculated or complicated effusions

---

Pleurisy (Related Condition)

Definition: Inflammation of the pleura causing sharp, positional chest pain.

Etiologies: Viral (most common), bacterial, TB, autoimmune (SLE, RA), pulmonary, cardiac, drugs.

Clinical Features:

• Sharp chest pain worsening with inspiration

• Pleural friction rub

• May have dry cough or dyspnea

Management:

• NSAIDs for pain

• Treat underlying cause