A pleural effusion is a collection of fluid in the pleural space that is usually caused by an underlying disease or condition. Common causes include congestive heart failure, pneumonia, liver disease, cancer, and pulmonary embolism. Pleural effusions are classified as transudative or exudative depending on the characteristics of the fluid. Treatment involves treating the underlying cause as well as draining large or infected effusions through procedures like thoracentesis or chest tube placement. Nurses play an important role in caring for patients with pleural effusions by managing drainage systems, providing pain relief, and educating patients.