Pleural Effusion

Definition and Normal Physiology

Classification: Transudate vs. Exudate

Light's Criteria (Exudate if ANY one is met):

• Rosen's Emergency Medicine, p. 990

Causes

Transudates

• Congestive heart failure (most common in the USA)
• Cirrhosis with ascites (hepatic hydrothorax)
• Nephrotic syndrome
• Hypoalbuminemia
• Myxedema
• Peritoneal dialysis
• Glomerulonephritis

Exudates

• Bacterial pneumonia / parapneumonic effusion / empyema
• Malignancy (lung, breast metastases are most common causes of massive effusion)
• Tuberculosis (classic cause in endemic regions)
• Pulmonary embolism
• Collagen vascular disease (rheumatoid, SLE)
• Pancreatitis (typically left-sided)
• Esophageal rupture (rare but highly morbid)
• Ovarian hyperstimulation syndrome
• Rosen's Emergency Medicine, p. 988

Laterality Clues

• Right-sided: ascites, heart failure, liver abscess
• Left-sided: pancreatitis, pericarditis, esophageal rupture, aortic dissection
• Bilateral: most often transudates (heart failure, nephrotic, hypoalbuminemia); bilateral exudates suggest metastatic disease, lymphoma, PE, SLE, myxedema
• Massive effusion: most commonly malignancy (lung or breast metastases), but also heart failure, cirrhosis, TB, empyema, trauma
• Grainger & Allison's Diagnostic Radiology, p. 62

Pleural Fluid Analysis

• Rosen's Emergency Medicine, pp. 990-991

Imaging

Chest X-Ray

1. Small (<200 mL): may be undetectable on erect PA; fluid collects under lower lobes (subpulmonary effusion)
2. 200-500 mL: posterior then lateral costophrenic angle blunting
3. Larger: homogeneous opacification of lower chest with obliterated costophrenic angle and hemidiaphragm; superior margin is concave to the lung and higher laterally (meniscus sign)
4. ~1000 mL: effusion reaches level of the 4th anterior rib
5. Massive: dense opacification of the hemithorax; may cause mediastinal shift to the contralateral side

• Grainger & Allison's Diagnostic Radiology, pp. 61-63

Ultrasound

• More sensitive than CXR; detects effusions as small as 50 mL
• Simple transudates appear hypoechoic (anechoic) above the diaphragm
• Complex exudates: heterogeneous echogenicity, fibrinous strands, septations, loculations
• Swirling echoes suggest high cellularity (malignant effusion)
• Compressed lung tissue often visible within the effusion
• Strongly preferred to guide thoracentesis - significantly reduces iatrogenic pneumothorax risk
• Rosen's Emergency Medicine, pp. 989-990

CT

• Best for characterizing the pleural space, identifying loculations, pleural thickening/enhancement (suggesting exudate), and underlying parenchymal pathology

Special Types

Hepatic Hydrothorax

• Complicates ~5-10% of patients with cirrhosis
• Caused by small diaphragmatic defects allowing ascitic fluid to pass into the pleural space
• 85% are right-sided; may exist even without detectable ascites
• Nearly all are transudative (unless infected)
• Management: sodium restriction + diuretics → TIPS (70-80% initial response, limited by encephalopathy) → VATS with pleurodesis → indwelling pleural catheters (palliation or bridge to transplant)
• Conventional chest tube drainage is NOT recommended (protein/electrolyte loss, infection, renal failure)
• Murray & Nadel's Textbook of Respiratory Medicine, p. (hepatic disease chapter)

Parapneumonic Effusion / Empyema

• Associated with bacterial pneumonia or lung abscess
• Empyema = frank pus in the pleural space
• Loculated effusion: fluid trapped by adhesions between parietal and visceral pleura
• pH < 7.0 is an indication for chest tube drainage
• Small-bore pigtail catheters (14 Fr) are now accepted first-line over large-bore tubes (28-40 Fr)
• Rosen's Emergency Medicine, p. 989, 991

Hemodynamic Effects

Management

When to Perform Thoracentesis

• Diagnostic: most effusions of unknown cause (can defer if obvious CHF and bilateral)
• Urgent therapeutic: massive effusions (>1.5-2 L) causing respiratory/circulatory compromise; empyema for source control
• ED indications: life-threatening pathology (empyema, esophageal rupture) or significant symptomatic relief needed

Contraindications (Relative)

• Coagulopathy / bleeding disorders
• History of pleurodesis
• Chest wall infection
• Pleural adhesions (risk reducible with ultrasound guidance)

Volume Limits

• Remove no more than 1500 mL per single procedure (British Thoracic Society, Grade C) to reduce the risk of re-expansion pulmonary edema
• Re-expansion pulmonary edema (rare): symptoms usually mild; treat with O2 and gentle diuresis

Complications of Thoracentesis

• Iatrogenic pneumothorax (most common - minimized by ultrasound guidance)
• Hemothorax
• Lung laceration
• Infection
• Transient hypoxia (V/Q mismatch)
• Hypotension (especially in volume-depleted patients)
• Re-expansion pulmonary edema

Key Summary Table