Pleural Disease

The pleural space normally holds less than 15 mL of fluid and is kept subatmospheric (roughly -3 to -5 cmH2O) by the opposing forces of lung elastic recoil and chest wall expansion. Fluid volume at any moment reflects a dynamic balance between filtration from pleural capillaries and clearance through parietal pleural lymphatics.

An effusion is exudative if it meets at least one of: pleural fluid/serum protein ratio >0.5, pleural fluid/serum LDH ratio >0.6, or pleural fluid LDH >2/3 the upper limit of normal for serum LDH. Combined sensitivity is ~97% but specificity is only ~85%, so roughly one transudate in four is mislabeled as an exudate.

About 25% of transudates — classically in a heart-failure patient already treated with loop diuretics — meet exudative Light's criteria because diuresis concentrates pleural protein and LDH. When the clinical story still fits a transudative process, a serum-to-pleural protein gradient (SPPG) >3.1 g/dL or a serum-to-pleural albumin gradient (SPAG) >1.2 g/dL reclassifies the effusion as a transudate (sensitivity ~100% in heart failure, ~99% in hepatic hydrothorax).

Transudates arise from hydrostatic-oncotic imbalance across an intact pleural membrane — most commonly heart failure and cirrhosis, also nephrotic syndrome, hypoalbuminemia, peritoneal dialysis, and urinothorax. Exudates arise from inflammation-driven capillary leak or impaired lymphatic drainage — most commonly parapneumonic effusion and malignancy, also pulmonary embolism, tuberculosis, and autoimmune disease (RA, SLE).

In the setting of pneumonia, chest tube drainage is indicated when there is gross pus, a positive Gram stain or culture, loculated fluid, pH <7.20, glucose <60 mg/dL (3.3 mmol/L), or pleural LDH >1000 U/L. Antibiotics alone cannot sterilize a complicated effusion or empyema, and delayed drainage is the main modifiable driver of treatment failure; untreated fibrinopurulent effusions organize into a restrictive pleural peel requiring decortication.

Empyema is frank bacterial infection of the pleural space, defined by pus or a positive Gram stain. Up to half of community-acquired pneumonias produce a parapneumonic effusion and ~10% progress to pleural space infection; anaerobes grow in >20% of cases, so empiric antibiotics must cover them. Management is chest tube drainage plus antibiotics, with VATS adhesiolysis if drainage fails and decortication reserved for failure of both.

The MIST2 trial established combined intrapleural tPA (10 mg) plus DNase (5 mg) twice daily for 3 days as the medical standard for pleural infection, improving radiographic clearance and reducing surgical referral; neither agent alone helped. BTS 2023 explicitly endorses a reduced-dose regimen (tPA 5 mg plus DNase 5 mg) as potentially equally effective and preferable when bleeding risk is high.

Pleural fluid cytology is positive in only ~60% of malignant effusions overall (~79% adenocarcinoma, ~6% mesothelioma); if negative, proceed to image-guided needle biopsy, with thoracoscopic biopsy as the gold standard (>90%). Management is palliative (median survival 4-7 months): an indwelling pleural catheter (IPC) gives outpatient drainage with ~50% spontaneous pleurodesis within 6-8 weeks and is first-line per BTS 2023, while talc pleurodesis succeeds in 60-90% but fails in trapped lung. The OPTIMUM trial (2024) showed a fully ambulatory IPC pathway is quality-of-life-equivalent to inpatient talc slurry.

A large pneumothorax is defined by a rim of more than 2 cm between the lung margin and the chest wall at the level of the hilum on chest radiograph. CT is the most sensitive modality (indispensable in bullous emphysema, where bullae mimic pneumothorax); at the bedside, absent lung sliding suggests and a lung point confirms pneumothorax on ultrasound.

Small (<2 cm), minimally symptomatic pneumothorax: needle aspiration or observation with supplemental oxygen (PSP may be managed as an outpatient if access to care is good). Large (>2 cm) with breathlessness and chest pain: small-bore (<14 Fr) thoracostomy tube on high-volume, low-pressure suction. Cardiovascular compromise regardless of size: emergent needle decompression followed by chest tube insertion. Persistent air leak >48 h: refer to an interventional pulmonologist or thoracic surgeon.

Recurrence prevention (chemical or mechanical pleurodesis; thoracoscopy with bleb stapling plus surgical pleurodesis is nearly 100% effective) is indicated after the second ipsilateral PSP and after the first SSP. Recurrence risk after a first PSP is 23-50% within 1-5 years; after SSP it exceeds 50% within 1-3 years. Smoking cessation is nonnegotiable: lifetime PSP incidence is 12% in male heavy smokers versus 0.1% in never-smokers.

Tension pneumothorax is a clinical diagnosis — do not wait for imaging. Suspect it in significant cardiorespiratory distress with hypotension, unilateral absent breath sounds, tracheal deviation, and distended neck veins; positive pleural pressure throughout the respiratory cycle collapses venous return and cardiac output. Decompress immediately with a large-bore needle in the second anterior intercostal space, leave the needle in place until a chest tube is inserted, and hospitalize.

Hepatic hydrothorax complicates about 5% of patients with cirrhosis and ascites: peritoneal fluid tracks through small diaphragmatic defects into the pleural space, usually on the right, and can become spontaneously infected (spontaneous bacterial empyema). The fluid is transudative. Treatment is that of the ascites — sodium restriction and diuretics — with pleurodesis, transjugular intrahepatic portosystemic shunt (TIPS), or liver transplantation for refractory cases.

Chylothorax follows disruption of the thoracic duct — most often thoracic surgery or trauma, also mediastinal tumors — and is confirmed by pleural fluid triglycerides >110 mg/dL (values 50-110 mg/dL require lipoprotein testing for chylomicrons). Management is chest tube drainage plus octreotide and elimination of enteral fat; refractory leaks are controlled with percutaneous thoracic duct embolization or surgical ligation. A cholesterol effusion (pseudochylothorax) from long-standing TB or rheumatoid pleurisy looks identical but has low triglycerides.

The 2024 joint European guideline (24 GRADE recommendations updating the 2015 ERS statement) conditionally recommends conservative management for minimally symptomatic, clinically stable PSP, codifying a 2020 randomized trial showing observation is a safe alternative to intervention. When an intervention is needed, there is a strong recommendation for needle aspiration over chest tube as the initial procedure. Ambulatory management with a Heimlich valve is conditionally supported, and an autologous blood patch is conditionally recommended for persistent air leak in SSP.