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Emergency And Acute Medicine – Pleural Effusion
Pleural effusion is the abnormal accumulation of fluid within the pleural space. Under normal conditions, the pleural cavity contains approximately 0.1–0.2 mL/kg of clear, low-protein fluid that facilitates lung movement within the thorax. Fluid balance is governed by hydrostatic and oncotic forces, with formation primarily from the parietal pleura and reabsorption through the visceral pleura and lymphatics. Disruption of these forces or lymphatic drainage results in fluid accumulation.
Effusions are classified as transudative or exudative. Transudative effusions are low in protein and cells and result from increased hydrostatic pressure or decreased oncotic pressure without primary pleural disease. Common causes include congestive heart failure, cirrhosis with ascites, nephrotic syndrome, peritoneal dialysis, pulmonary embolism, and hypoalbuminemia. Exudative effusions contain higher protein and cellular content and result from pleural inflammation or impaired lymphatic drainage. Causes include pneumonia, tuberculosis, malignancy, mesothelioma, metastatic disease, pulmonary embolism, pancreatitis, subdiaphragmatic abscess, esophageal rupture, rheumatologic disease, trauma, hemothorax, chylothorax, and certain medications.
Small effusions are often asymptomatic. Larger effusions may cause dyspnea, pleuritic chest pain, cough, tachypnea, and hypoxia. Physical examination may reveal decreased breath sounds, decreased tactile fremitus, dullness to percussion, increased egophony above the fluid level, and occasionally a pleural friction rub. Evaluation should also focus on identifying the underlying cause such as heart failure, infection, or malignancy.
Initial workup includes cardiac monitoring, pulse oximetry, laboratory studies including complete blood count and metabolic panel, and chest imaging. Upright chest radiography typically shows blunting of the costophrenic angle and requires approximately 200–250 mL of fluid for detection. Lateral decubitus films or bedside ultrasound can detect as little as 5–10 mL of fluid and help differentiate free-flowing from loculated effusions. Ultrasound improves safety and reduces pneumothorax risk during thoracentesis. CT of the chest with intravenous contrast is the most sensitive imaging modality and is useful for identifying loculated collections and underlying pulmonary or pleural pathology. Pulmonary embolism should always be considered in cases of unexplained effusion.
Thoracentesis is indicated for new effusions in ill patients or for symptomatic relief of dyspnea due to large effusions. Fluid analysis distinguishes transudative from exudative effusions using Light criteria. An effusion is exudative if one or more of the following are present: pleural fluid protein to serum protein ratio greater than 0.5, pleural fluid LDH to serum LDH ratio greater than 0.6, or pleural fluid LDH greater than two-thirds the upper limit of normal serum LDH. Exudative effusions require further analysis including cell count, Gram stain, culture, cytology, pH, glucose, and other tests guided by clinical suspicion. A pleural fluid hematocrit greater than half of serum hematocrit defines hemothorax. A pH less than 7 or glucose less than 60 mg/dL suggests complicated parapneumonic effusion or empyema.
Therapeutic thoracentesis should avoid removal of more than 1,500 mL to reduce the risk of re-expansion pulmonary edema. Indications for tube thoracostomy include empyema, complicated parapneumonic effusion with low pH or glucose, positive Gram stain or culture, loculated effusion, or hemothorax. Post-procedure chest radiography is recommended to evaluate for pneumothorax.
Emergency management includes airway, breathing, and circulation stabilization with supplemental oxygen and intravenous access. Emergent thoracentesis is required for significant respiratory compromise. Treatment is directed at the underlying cause. Heart failure–related effusions require diuresis. Parapneumonic effusions require antibiotics. Pulmonary embolism requires anticoagulation, and the presence of bloody effusion is not a contraindication. Rheumatologic effusions may respond to anti-inflammatory therapy. Loculated effusions may require intrapleural fibrinolytics or surgical intervention.
Admission is indicated for respiratory compromise, unknown etiology, empyema, suspected parapneumonic effusion, or complications of thoracentesis. Intensive care is required for severe respiratory or hemodynamic instability. Discharge may be considered when the cause is identified, respiratory status is stable, and appropriate follow-up is arranged.
The most common causes of pleural effusion are congestive heart failure, pneumonia, and malignancy. Failure to recognize life-threatening causes such as pulmonary embolism, esophageal rupture, or hemothorax can result in significant morbidity and mortality. Bedside ultrasound is invaluable in diagnosis and procedural guidance and should be used whenever available.
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