Pleural Effusion

🔹 Pleural Space Characteristics

  • Normally contains 5–15 mL of fluid
  • Fluid functions as:
    • Lubricant between pleural surfaces
    • Allows smooth lung movement during respiration


🔹 Pleural Fluid Formation

Sources

  1. Systemic capillaries of parietal pleura (major source)
  2. Pulmonary capillaries of visceral pleura
  3. Interstitial lung fluid


🔹 Pleural Fluid Absorption

  • Mainly via:
    • Parietal pleural lymphatics
  • Absorption capacity is large → Effusion occurs when production overwhelms removal.


Pathophysiology of Pleural Effusion

Pleural effusions occur via five major mechanisms:

Mechanism

Example

↑ Hydrostatic pressure

Heart failure

↓ Oncotic pressure

Hypoalbuminemia

↑ Capillary permeability

Pneumonia, ARDS

Impaired lymphatic drainage

Malignancy

Movement from abdomen

Cirrhosis, pancreatitis


Classification of Pleural Effusion


1️⃣ Transudative Effusion

Mechanism

  • Systemic fluid imbalance without pleural inflammation

Causes

  • Congestive heart failure (most common)
  • Cirrhosis (hepatic hydrothorax)
  • Nephrotic syndrome
  • Hypoalbuminemia
  • Peritoneal dialysis


2️⃣ Exudative Effusion

Mechanism

  • Local pleural inflammation or disease

Causes

  • Pneumonia (parapneumonic effusion)
  • Tuberculosis
  • Malignancy
  • Pulmonary embolism
  • Autoimmune diseases
  • Pancreatitis
  • Esophageal rupture


Radiological Appearance of Pleural Effusion

Chest X-ray Features

Classic Signs

  • Blunting of costophrenic angle (>200 mL fluid)
  • Meniscus sign
  • Homogenous opacity
  • Mediastinal shift (large effusion)


Ultrasound Features (ICU Gold Standard)

  • Spine sign = earliest detection

Normally:Spine visible only below diaphragm but In pleural effusion:
 Vertebral bodies become visible ABOVE diaphragm as Fluid conducts ultrasound waves → allows visualization of thoracic spine.

  • Sinusoid sign = confirms free fluid(Seen on M-mode ultrasound.

Shows cyclic movement of lung toward and away from chest wall during respiration.)

  • Jellyfish sign = floating atelectatic lung
  • Septations = complicated effusion
  • Plankton sign = exudate


Advantages

  • Detects as little as 5–50 mL
  • Guides thoracentesis
  • Differentiates:
    • Simple vs loculated effusion
    • Effusion vs consolidation


CT Helps Identify

  • Pleural thickening
  • Empyema (split pleura sign)
  • Malignancy
  • Lung parenchymal pathology


Clinical Presentation

Symptoms

  • Dyspnea (most common)
  • Pleuritic chest pain
  • Cough
  • Fever (infective effusion)


Physical Examination

Finding

Explanation

Reduced chest expansion

Lung compression

Stony dull percussion

Fluid presence

Reduced breath sounds

Fluid barrier

Reduced tactile fremitus

Sound dampening


Diagnostic Approach

🔹 Step 1: Confirm Effusion (Imaging)

  • CXR
  • Lung ultrasound (preferred in ICU)
  • CT if unclear etiology


🔹 Step 2: Diagnostic Thoracentesis (Most Important Step)

Indications

  • New effusion >1 cm thickness
  • Unknown cause
  • Suspected infection or malignancy

Pleural Fluid Analysis

 Light’s Criteria 

Effusion is exudate if ANY ONE present:

Parameter

Cutoff

Pleural fluid protein / Serum protein

>0.5

Pleural fluid LDH / Serum LDH

>0.6

Pleural LDH

>2/3 upper limit normal serum LDH


Pitfall (Very )

  • CHF patients on diuretics → May falsely appear exudative
    👉 Use Serum-pleural albumin gradient >1.2 g/dL = Transudate


Pleural Fluid Interpretation Table

Parameter

Suggests

Low pH (<7.2)

Empyema

Low glucose

TB, malignancy, RA

High amylase

Pancreatitis, esophageal rupture

High triglyceride

Chylothorax

Lymphocyte predominant

TB, malignancy

Neutrophil predominant

Parapneumonic effusion



Management of Pleural Effusion

⭐ Stepwise Management Strategy

Step 1 – Treat Underlying Cause

Cause

Therapy

CHF

Diuretics

TB

Anti-tubercular therapy

Pneumonia

Antibiotics

Malignancy

Pleurodesis / catheter


Step 2 – Therapeutic Thoracentesis

Indications

  • Symptomatic dyspnea
  • Large effusion

Volume Threshold Causing Symptoms

There is no absolute fluid volume cutoff, but clinical correlation is crucial.

Approximate Symptomatic Volumes

Fluid Volume

Clinical Effect

<300 mL

Usually asymptomatic

300–1000 mL

Mild dyspnea possible

>1000 mL

Usually symptomatic

>1500–2000 mL

Severe dyspnea & lung compression

👉 Most guidelines recommend drainage when:

  • Effusion occupies >25–33% hemithorax
  • Ultrasound thickness >2–2.5 cm


Volume Removal Rule 

  • Remove ≤1–1.5 L per session
  • Prevent re-expansion pulmonary edema


Chest Tube Drainage

Indications

  • Empyema
  • Complicated parapneumonic effusion
  • Hemothorax
  • Chylothorax


Pleurodesis

Indications

  • Recurrent malignant effusion

Agents

  • Talc (most effective)
  • Doxycycline
  • Bleomycin



Complications of Pleural Effusion

  • Respiratory failure
  • Fibrothorax
  • Empyema
  • Sepsis
  • Trapped lung


Complications of Thoracentesis

  • Pneumothorax
  • Bleeding
  • Infection
  • Re-expansion pulmonary edema


Re-Expansion Pulmonary Edema 

Risk Factors

  • Rapid drainage
  • Large effusion
  • Chronic lung collapse

Prevention

  • Limit drainage volume
  • Monitor symptoms



Guideline & Textbook References

  • Harrison’s Principles of Internal Medicine
  • British Thoracic Society Pleural Disease Guidelines
  • ATS/ERS Pleural Disease Recommendations
  • Light RW Pleural Disease Textbook
  • StatPearls Pleural Effusion Review