A pleural effusion is an abnormal collection of fluid in the pleural space resulting from excess fluid production or decreased absorption.
It is the most common manifestation of pleural disease. The pleural space is bordered by the parietal and visceral pleurae. The parietal pleura covers the inner surface of the thoracic cavity, including the mediastinum, diaphragm, and ribs. The visceral pleura envelops all lung surfaces, including the interlobar fissures. The right and left pleural spaces are separated by the mediastinum.
The pleural space plays an important role in respiration by coupling the movement of the chest wall with that of the lungs in two ways. First, a relative vacuum in the space keeps the visceral and parietal pleurae in close proximity. Second, the small volume of pleural fluid, which has been calculated at 0.13 mL/kg of body weight under normal circumstances, serves as a lubricant to facilitate movement of the pleural surfaces against each other in the course of respirations.
This small volume of fluid is maintained through the balance of hydrostatic and oncotic pressure and lymphatic drainage, a disturbance of which may lead to pathology.
(See the images below.)
Anteroposterior upright chest radiograph shows a massive left-sided pleural effusion with contralateral mediastinal shift. Image courtesy of Allen R. Thomas, MD.
Left lateral decubitus chest radiograph shows fluid layering on the left side, which is not a loculated effusion. Image courtesy of Allen R. Thomas, MD.
Most commonly, a pleural effusion is an incidental finding in a stable patient. Prehospital interventions are generally limited to patients who are in respiratory distress or are hemodynamically unstable.
As with any other life-threatening condition, initial management is directed at ensuring adequate oxygenation and ventilation. Oxygen should be administered to all unstable patients. After airway stabilization, the patient’s circulatory status should be assessed and supported as indicated.
After the initial stabilization of the patient, clinical suspicion for pleural effusion should be confirmed with appropriate radiographic evaluation. Chest radiography is the primary diagnostic tool. Emergency physicians may rapidly perform ultrasonography of the chest to evaluate patients with suspected pleural effusion. A spiral chest CT scan should be obtained for most patients with pleural effusion when the condition’s etiology cannot be readily determined or when complicated pleural effusion (eg, empyema, malignancy) is suspected.
Diagnostic procedures include percutaneous pleural biopsy, bronchoscopy, thoracoscopy, and open pleural biopsy.
Laboratory evaluation of patients with a pleural effusion is directed at first determining if the effusion is an exudate or a transudate. The distinction between transudate and exudate is generally made by measurement of serum and pleural fluid lactate dehydrogenase (LDH) and protein concentrations.
Strict precautions are required in the handling of needles and bodily fluids, including pleural fluid. Reports exist of human immunodeficiency virus (HIV) transmission from needles contaminated with pleural fluid.