# Pleural Disease - Effusions and Pneumothorax

## Pleural Effusion - Approach

### Pathophysiology

Under normal physiologic conditions, the pleural space contains 0.1-0.3 mL/kg of fluid, produced by the parietal pleural capillaries and absorbed by the parietal pleural lymphatics under the influence of Starling forces. A pleural effusion accumulates when fluid production exceeds absorption, a state that can arise through several mechanisms: increased capillary hydrostatic pressure (as in heart failure), decreased plasma oncotic pressure (as in hypoalbuminemia), increased capillary permeability (as in infection or inflammation), impaired lymphatic drainage (as in malignancy or chylothorax), or transdiaphragmatic passage of fluid from the peritoneal cavity (as in hepatic hydrothorax).

### Initial Evaluation

The minimum volume required for detection varies by imaging modality: approximately 200 mL on upright posteroanterior chest radiography, identified by blunting of the costophrenic angle; 50 mL on lateral decubitus imaging; and as little as 20 mL with ultrasound. Point-of-care ultrasound (POCUS) has become indispensable in pleural disease evaluation, as it identifies the presence of an effusion, estimates volume, guides thoracentesis to reduce the risk of pneumothorax to less than 1%, and characterizes effusion complexity by identifying septations and echogenicity. CT chest with contrast provides comprehensive evaluation of the lung parenchyma, mediastinum, and pleural surfaces, where pleural thickening or nodularity may suggest malignancy or empyema.

### Light's Criteria (Exudate vs. Transudate)

Light's criteria remain the standard method for differentiating exudative from transudative effusions. An effusion is classified as exudative if any one of the following criteria is met: a pleural fluid protein to serum protein ratio exceeding 0.5, a pleural fluid LDH to serum LDH ratio exceeding 0.6, or a pleural fluid LDH exceeding two-thirds the upper limit of normal for serum LDH. These criteria achieve a sensitivity for identifying exudates of approximately 98% and a specificity of approximately 80%. A well-recognized limitation is misclassification: diuretic use may cause transudative effusions to meet exudative criteria. In this clinical scenario, the serum-pleural fluid albumin gradient (greater than 1.2 g/dL supports a transudate) or the pleural fluid protein gradient (serum minus pleural protein greater than 3.1 g/dL) can be used to reclassify the effusion correctly.

### Common Causes

Transudative effusions are caused by congestive heart failure (the most common cause of pleural effusion overall), hepatic hydrothorax, nephrotic syndrome, peritoneal dialysis, hypoalbuminemia, and constrictive pericarditis. Exudative effusions arise from parapneumonic processes and empyema, malignancy, pulmonary embolism, tuberculosis, autoimmune diseases (rheumatoid arthritis, SLE), drug reactions, pancreatitis, chylothorax, hemothorax, and post-cardiac surgery.

<image>A diagnostic algorithm for pleural effusion evaluation. Start with detection on imaging. First step: clinical assessment for obvious cause (CHF, pneumonia). If no obvious cause or diagnostic uncertainty: thoracentesis with POCUS guidance. Analyze fluid: appearance (straw, bloody, milky, purulent), cell count and differential, protein, LDH, glucose, pH. Apply Light's criteria: transudate vs. exudate. For transudates: treat underlying cause (CHF, cirrhosis). For exudates: further branch based on appearance and labs - if purulent or pH < 7.20: complicated parapneumonic/empyema (chest tube); if bloody: consider malignancy, PE, hemothorax (send cytology, check hematocrit); if lymphocyte-predominant: consider TB (ADA), malignancy (cytology), lymphoma; if milky/chylous: check triglycerides (>110 mg/dL = chylothorax). Include subsequent investigations: pleural biopsy if cytology negative x 2-3, CT chest, PET-CT for malignancy. Use color-coded pathways.</image>

## Pleural Fluid Analysis

### Routine Studies

The macroscopic appearance of pleural fluid provides immediate diagnostic clues: straw-colored fluid suggests a transudate, cloudy or turbid fluid indicates an exudate, frankly purulent fluid confirms empyema, bloody fluid raises concern for malignancy, pulmonary embolism, or trauma, and milky white fluid suggests chylothorax or pseudochylothorax. Cell count and differential analysis provides further discrimination: a neutrophilic predominance points toward bacterial infection, pulmonary embolism, or early tuberculosis; a lymphocytic predominance suggests tuberculosis, malignancy, lymphoma, sarcoidosis, or post-cardiac surgery; and eosinophilia exceeding 10% of the differential may indicate air or blood in the pleural space, drug reaction, parasitic infection, malignancy, or eosinophilic granulomatosis with polyangiitis. Protein and LDH measurements are necessary for applying Light's criteria. Glucose levels below 60 mg/dL are found in empyema, malignancy, rheumatoid arthritis, tuberculosis, and lupus pleuritis, while levels below 40 mg/dL are strongly suggestive of empyema or rheumatoid effusion. Pleural fluid pH below 7.20 indicates a complicated parapneumonic effusion requiring drainage and is also found in empyema, malignancy, rheumatoid arthritis, and esophageal rupture; pH must be measured on a blood gas analyzer, not with pH strips.

### Specialized Studies

| Test | Result | Diagnosis Suggested | Sensitivity/Specificity |
|------|--------|-------------------|------------------------|
| Cytology | Malignant cells | Malignant effusion | 60% (1st), 75% (repeat) |
| ADA | > 40 U/L | Tuberculous pleuritis | 92% / 90% |
| Triglycerides | > 110 mg/dL | Chylothorax | Confirmatory |
| Triglycerides | < 50 mg/dL | Excludes chylothorax | Exclusionary |
| Cholesterol | > 200 mg/dL | Pseudochylothorax | Confirmatory |
| Amylase | Elevated | Pancreatitis, esophageal rupture, malignancy | Variable |
| Hematocrit (pleural/blood) | > 0.5 | Hemothorax | Confirmatory |
| BNP | > 1500 pg/mL | CHF | Strongly supportive |

Cytology achieves a sensitivity of approximately 60% on the first sample, rising to 75% with repeat sampling, with the highest yield in adenocarcinoma and mesothelioma. Adenosine deaminase (ADA) levels exceeding 40 U/L provide a sensitivity of 92% and specificity of 90% for tuberculous pleuritis in high-prevalence settings, while levels below 40 essentially exclude the diagnosis. Pleural fluid triglycerides exceeding 110 mg/dL confirm chylothorax, levels below 50 mg/dL exclude it, and intermediate values (50-110 mg/dL) should prompt analysis for chylomicrons. Cholesterol levels exceeding 200 mg/dL indicate pseudochylothorax, a condition associated with chronic trapped lung. Elevated amylase suggests pancreatitis, esophageal rupture, or malignancy. A pleural to blood hematocrit ratio exceeding 0.5 confirms hemothorax. Pleural fluid BNP exceeding 1500 pg/mL strongly supports CHF as the underlying cause.

## Specific Pleural Conditions

### Parapneumonic Effusion and Empyema

Parapneumonic effusions progress through three stages of increasing severity: simple parapneumonic effusion (a sterile exudate), complicated parapneumonic effusion (characterized by pH below 7.20, glucose below 60, positive gram stain or culture, and loculations), and empyema (frank pus). Chest tube drainage is required when any of the following are present: frank pus, positive gram stain or culture, pH below 7.20, glucose below 40 mg/dL, or a loculated effusion. Intrapleural fibrinolytic therapy was definitively evaluated in the MIST2 trial, which demonstrated that the combination of tPA 10 mg plus DNase 5 mg administered via chest tube twice daily for 3 days significantly reduced surgical referral and hospital length of stay. A critical finding of this trial was that neither tPA alone nor DNase alone was effective; the combination is essential. VATS decortication is pursued when fibrinolytic therapy fails or when an organized empyema is present.

### Malignant Pleural Effusion

The most common causes of malignant pleural effusion are lung cancer, breast cancer, lymphoma, and mesothelioma. The prognosis is guarded, with median survival of 3-12 months depending on the primary malignancy. Management options include therapeutic thoracentesis for symptomatic relief, though the recurrence rate approaches 100% within 30 days. Indwelling pleural catheters (IPCs) enable outpatient drainage and achieve spontaneous pleurodesis in 40-50% of patients over time; the IPC-PLUS trial demonstrated that combining an IPC with talc slurry instillation through the catheter was superior to IPC alone for achieving pleurodesis. Talc pleurodesis, delivered as slurry (4-5 g talc in 50 mL saline via chest tube) or poudrage (insufflation of graded talc via VATS), achieves success rates of 70-80%. The AMPLE-2 trial demonstrated that IPC was non-inferior to talc pleurodesis for quality of life, and patient preference should guide the choice between these approaches. For patients with trapped lung, IPC is preferred since pleurodesis is unlikely to succeed.

### Hepatic Hydrothorax

Hepatic hydrothorax occurs on the right side in 85% of cases, complicating portal hypertension through fluid transit via diaphragmatic defects. The effusion is transudative, and first-line management consists of sodium restriction and diuretics. Chest tubes should be avoided due to the risks of massive fluid output, protein depletion, and infection. Transjugular intrahepatic portosystemic shunt (TIPS) is the intervention of choice for diuretic-refractory hepatic hydrothorax, as it reduces portal pressure. IPC may be considered when TIPS is contraindicated or ineffective, though infection risk is higher in cirrhotic patients.

### Tuberculous Pleural Effusion

Tuberculous pleural effusion presents as a lymphocyte-predominant exudate with ADA exceeding 40 U/L strongly suggestive of the diagnosis. Pleural fluid AFB smear has a sensitivity below 5%, and culture achieves positivity in only 20-30%. Pleural biopsy, either closed or thoracoscopic, demonstrates granulomas in 60-80% and achieves culture positivity in 50-70% of cases. Treatment follows the standard six-month anti-tuberculosis regimen (2RIPE/4RI), and the role of adjunctive corticosteroids remains debated, though they may reduce adhesion formation.

<image>A comparison infographic of management options for malignant pleural effusion. Display three columns: (1) Repeated therapeutic thoracentesis - show procedure image, advantages (simple, office-based), disadvantages (recurrence, repeated procedures, protein loss), best for (limited life expectancy, uncertain diagnosis). (2) Indwelling pleural catheter (IPC) - show catheter placement diagram, advantages (outpatient, trapped lung amenable), disadvantages (infection risk 5%, daily drainage burden), success rate for spontaneous pleurodesis. (3) Talc pleurodesis - show VATS poudrage and slurry via chest tube illustrations, advantages (definitive, high success rate), disadvantages (inpatient, chest pain, ARDS risk with non-graded talc), contraindication (trapped lung). Include the TIME2/AMPLE2 trial evidence supporting equivalence. Show decision algorithm at bottom: expandable lung → either IPC or talc pleurodesis based on preference; trapped lung → IPC.</image>

## Pneumothorax

### Classification

Primary spontaneous pneumothorax (PSP) occurs in individuals without clinically apparent underlying lung disease, typically affecting tall, thin males between 20-30 years of age through rupture of apical blebs or bullae. Secondary spontaneous pneumothorax (SSP) occurs in the setting of underlying lung disease, including COPD, cystic fibrosis, LAM, Marfan syndrome, PLCH, Pneumocystis pneumonia, and tuberculosis. Traumatic pneumothorax results from penetrating or blunt chest trauma, or iatrogenic causes including central line placement, thoracentesis, transbronchial biopsy, and mechanical ventilation. Catamenial pneumothorax is associated with the menstrual cycle due to thoracic endometriosis, is characteristically right-sided, and tends to recur.

### BTS 2023 Guidelines for Management

For primary spontaneous pneumothorax, the BTS 2023 guidelines recommend the following approach. Asymptomatic, small pneumothoraces (less than 2 cm at the hilum) should be observed for 2-4 hours with discharge if the chest radiograph is stable, and follow-up at 2-4 weeks. Symptomatic PSP can be managed with ambulatory devices (such as the Atrium/Heimlich valve) in preference to hospital admission, as supported by the RAMPP trial, which demonstrated that ambulatory management with the Rocket pleural vent was non-inferior to standard chest tube placement with a shorter hospital stay. Alternatively, aspiration may be attempted with a success rate of 50-70%, with chest tube insertion if aspiration fails. When chest tube insertion is required, small-bore tubes (10-14 Fr) are preferred over large-bore tubes. For secondary spontaneous pneumothorax, admission is generally required given the higher risk of respiratory compromise. Small pneumothoraces with minimal symptoms may be managed with aspiration, but chest tube insertion is required for most cases, with small-bore tubes equivalent to large-bore in most studies except with active air leak. All SSP patients should be monitored closely.

### Indications for Surgery

Surgical intervention is indicated for recurrent ipsilateral pneumothorax (second or subsequent episode), first contralateral pneumothorax, bilateral spontaneous pneumothorax, persistent air leak exceeding 5-7 days, hemopneumothorax, and occupational risk factors (pilots, divers). The standard procedure is VATS with bullectomy or bleb resection combined with mechanical pleurodesis (pleural abrasion) or partial pleurectomy, achieving a recurrence rate below 5%.

### Tension Pneumothorax

Tension pneumothorax is a clinical diagnosis characterized by hypotension, tracheal deviation, absent breath sounds, distended neck veins, and tachycardia. Immediate needle decompression should be performed using a 14-16 gauge needle at the second intercostal space in the midclavicular line or, preferably, the fourth to fifth intercostal space in the anterior axillary line where the chest wall is thinner. Needle decompression must be followed by chest tube insertion.

## Key Clinical Pearls

- Light's criteria misclassify ~25% of CHF-related effusions as exudative after diuresis; use serum-pleural albumin gradient > 1.2 g/dL to reclassify
- In complicated parapneumonic effusion/empyema, the MIST2 regimen (tPA 10 mg + DNase 5 mg via chest tube BID x 3 days) significantly reduces surgical referral; neither agent alone is effective
- Pleural fluid pH < 7.20 is the single best predictor of need for chest tube drainage in parapneumonic effusion; it MUST be measured on a blood gas analyzer, not litmus paper
- Small-bore chest tubes (10-14 Fr) are as effective as large-bore tubes for most pneumothoraces and pleural effusions, with less pain
- Ambulatory management of PSP is now supported by the RAMPP trial and may become the new standard, reducing unnecessary hospitalizations

## References
1. Roberts ME, Rahman NM, Maskell NA, et al. British Thoracic Society Guideline for pleural disease. Thorax. 2023;78(Suppl 3):s1-s42.
2. Rahman NM, Maskell NA, West A, et al. Intrapleural Use of Tissue Plasminogen Activator and DNase in Pleural Infection. N Engl J Med. 2011;365(6):518-526. (MIST2)
3. Hallifax RJ, McKeown E, Sivakumar P, et al. Ambulatory management of primary spontaneous pneumothorax: an open-label, randomised controlled trial. Lancet. 2020;396(10243):39-49. (RAMPP)
4. Feller-Kopman D, Light R. Pleural Disease. N Engl J Med. 2018;378(8):740-751.
5. Thomas R, Fysh ETH, Smith NA, et al. Effect of an Indwelling Pleural Catheter vs Talc Pleurodesis via Thoracoscopy on Hospitalization Days in Patients With Malignant Pleural Effusion: The AMPLE Randomized Clinical Trial. JAMA. 2017;318(19):1903-1912.