pulmonary disorders
Pleural Effusion
Introduction
Pleural effusions are accumulations of fluid within the pleural space. They have multiple causes and are usually classified as transudates or exudates. Detection is by physical examination, chest x-ray, and bedside thoracic ultrasonography. Thoracentesis and pleural fluid analysis are often required to determine cause. Asymptomatic bilateral transudates require no treatment. Symptomatic transudates and most exudates require thoracentesis, chest tube drainage, and definitive pleural management (indwelling pleural catheter,talcpleurodesis, thoracic surgery, or a combination). Normally, 10 to 20 mL of pleural fluid, similar in composition to plasma but lower in protein (<1.5 g/dL [< 15 g/L]), is spread thinly over the visceral and parietal pleurae, facilitating movement between the lungs and chest wall. The fluid enters the pleural space from systemic capillaries in the parietal pleurae and exits via parietal pleural stomas and lymphatics. The fluid ultimately drains into the right atrium, so clearance is dependent on capillary and, in part, right-sided pressures. Pleural fluid accumulates when too much fluid enters or too little exits the pleural space. 