Step 2 CK · Internal Medicine · Pulmonology

Pleural Disease

Name: Pleural Disease
Creator: Veli Bakalov, MD

Light criteria, chest tubes, and the tension pneumothorax that can't wait

Pulmonology·Pleural, Mediastinal & Thoracic Oncology·5 min read·9 high-yield points·Reviewed by Veli Bakalov, MD @HemeOncBuddy

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Light's criteria: exudate if ANY of pleural/serum protein over 0.5, pleural/serum LDH over 0.6, or pleural LDH over 2/3 of the serum upper limit of normal; none met = transudate.
Transudates (intact capillaries): heart failure (most common overall), cirrhosis, nephrotic syndrome, hypoalbuminemia; exudates: pneumonia, malignancy, PE, TB, pancreatitis, autoimmune disease.
Light's criteria can mislabel a diuresed CHF effusion as an exudate; a serum-to-pleural albumin gradient over 1.2 g/dL confirms a transudate.
Low pleural glucose (under 60) and pH (under 7.2) mean complicated parapneumonic effusion/empyema, TB, malignancy, or rheumatoid pleuritis.
A parapneumonic effusion with pH under 7.2, glucose under 60, positive Gram stain/culture, or pus needs a chest tube; for loculations add intrapleural tPA + DNase, then VATS/decortication.
Chylothorax = milky fluid with triglycerides over 110 mg/dL (thoracic-duct injury, lymphoma); hemothorax = pleural hematocrit over 50% of blood; high amylase = pancreatitis or esophageal rupture.
Malignant effusion is a bloody exudate from lung cancer, breast cancer, or lymphoma; diagnose by cytology and palliate with thoracentesis, an indwelling catheter, or pleurodesis.
Primary spontaneous pneumothorax = tall, thin, young male smokers with ruptured apical blebs; small (under 2–3 cm) and stable → observe with O2; large, symptomatic, or secondary → aspiration or chest tube.
Tension pneumothorax (hypotension, JVD, absent breath sounds, trachea deviated away) is clinical: needle decompress (2nd ICS, midclavicular line) before imaging, then place a chest tube.

Pleural effusion: transudate or exudate?

Recognizing an effusion. Look for dullness to percussion, decreased breath sounds, and decreased tactile fremitus over the fluid. On x-ray the first sign is blunting of the costophrenic angle. The first diagnostic question is always whether the fluid is a transudate or an exudate.

Light's criteria. An effusion is an exudate if it meets any one of the three criteria:

Pleural/serum protein ratio >0.5
Pleural/serum LDH ratio >0.6
Pleural LDH >2/3 of the upper limit of normal for serum LDH

An effusion that meets none of them is a transudate. The criteria are very sensitive for exudates, so they occasionally mislabel a transudate.

Transudate vs exudate

Feature	Transudate	Exudate
Light's criteria	None met	Any one met
Mechanism	Altered hydrostatic or oncotic pressure; capillaries intact	Increased capillary permeability or impaired lymphatic drainage
Causes	Heart failure (most common overall), cirrhosis, nephrotic syndrome, hypoalbuminemia	Pneumonia (parapneumonic), malignancy, pulmonary embolism, tuberculosis, pancreatitis, autoimmune disease
Approach	Treat the cause; bilateral effusions with clear-cut CHF can be diuresed before any tap	A new unexplained exudate needs diagnostic thoracentesis with cytology and cultures

Diuresis concentrates pleural protein and LDH, so Light's criteria can mislabel a treated CHF transudate as an exudate. If you suspect this, a serum-to-pleural albumin gradient >1.2 g/dL confirms a transudate.

Reading the thoracentesis

The standard panel. Send protein and LDH (for Light's criteria), pH, glucose, a cell count with differential, Gram stain and culture, and cytology.

Low glucose and low pH. Glucose <60 mg/dL and pH <7.2 narrow the causes to a complicated parapneumonic effusion or empyema, TB, malignancy, or rheumatoid pleuritis. Rheumatoid effusions can have strikingly low glucose. A lymphocyte-predominant exudate points toward TB or malignancy, and a high adenosine deaminase supports TB.

Special pleural fluids

Finding	Diagnosis	Usual causes
Milky fluid; triglycerides >110 mg/dL; chylomicrons	Chylothorax	Thoracic-duct disruption (surgery such as esophagectomy, trauma); malignancy, especially lymphoma
Pleural hematocrit >50% of blood hematocrit	Hemothorax	Trauma, procedures
Exudate with high amylase	Pancreatic or esophageal source	Pancreatitis; esophageal rupture (which also drives pH very low)
Frank pus or organisms on Gram stain	Empyema	Untreated complicated parapneumonic effusion
Bloody exudate with malignant cells	Malignant effusion	Lung cancer, breast cancer, lymphoma

Parapneumonic, empyema, and malignant effusions

Complicated parapneumonic effusion. Any of the following makes a parapneumonic effusion complicated: pH <7.2, glucose <60, a positive Gram stain or culture, or frank pus (empyema). A complicated effusion needs chest-tube drainage, because antibiotics alone do not sterilize a closed, acidic space.

pH <7.2complicated parapneumonic effusion: drain it

Empyema. Empyema is pus in the pleural space. It evolves from an untreated complicated parapneumonic effusion.

Antibiotics plus chest tubeDrainage is mandatory once the fluid is complicated or purulent.
Intrapleural tPA plus DNaseFor loculations that prevent drainage.
VATS or decorticationSurgery if fibrinolytics fail or a thick peel traps the lung.

Malignant effusion. An exudate, often bloody. Lung cancer, breast cancer, and lymphoma are the leading causes. Fluid cytology makes the diagnosis but may need repeating, and a pleural biopsy is the next step if cytology stays negative. Malignant effusions tend to recur, so the goal is palliating dyspnea with therapeutic thoracentesis, an indwelling pleural catheter, or pleurodesis.

Spontaneous pneumothorax

Presentation. Sudden pleuritic chest pain and dyspnea. On the affected side, breath sounds and fremitus are decreased and the chest is hyperresonant. The x-ray shows a visceral pleural line with no lung markings beyond it, and bedside ultrasound shows absent lung sliding.

Types of pneumothorax

Type	Who and why	Management
Primary spontaneous	Tall, thin, young men and smokers; ruptured apical subpleural blebs; no known lung disease	Small (<2–3 cm) and stable: observe and give O2. Large or symptomatic: needle aspiration or chest tube
Secondary spontaneous	Underlying lung disease: COPD, cystic fibrosis, infection	Poorly tolerated: usually a chest tube
Tension	One-way valve traps air; often trauma or positive-pressure ventilation	Immediate needle decompression, then a chest tube

Why oxygen helps. Supplemental O2 lowers the nitrogen content of blood. The gradient then pulls nitrogen out of the pleural air, so the pneumothorax reabsorbs faster. Recurrent pneumothorax, or a first secondary one, is usually treated with pleurodesis or thoracoscopic bleb resection to prevent another episode.

Catamenial pneumothorax, from thoracic endometriosis, recurs with menses. Consider it in a young woman with repeated episodes.

Tension pneumothorax and chest-tube indications

A clinical diagnosis. Tension pneumothorax presents with progressive dyspnea, hypotension, distended neck veins, absent breath sounds on one side, and a trachea deviated away from that side. Rising intrathoracic pressure collapses venous return, which causes obstructive shock.

Recognize it clinicallyHypotension, JVD, absent breath sounds. Do not wait for a chest x-ray.
Needle decompression2nd intercostal space, midclavicular line. Current trauma teaching also accepts the 4th–5th space just anterior to the midaxillary line in adults.
Chest tubeDefinitive management after decompression.

The trachea shifts away from a tension pneumothorax or a massive effusion but toward a large atelectasis or collapsed lung.

Chest tube (tube thoracostomy) indications:

Large or symptomatic pneumothorax
Tension pneumothorax, after needle decompression
Empyema or complicated parapneumonic effusion
Hemothorax
Drainage of recurrent malignant effusions

In a traumatic hemothorax, initial chest-tube output of about 1,500 mL, or ongoing output over 200 mL/hr, points to bleeding that needs surgery.