1. A pleural effusion is a collection of fluid in the pleural space that is usually caused by an underlying condition such as heart failure, pneumonia, or cancer. 2. Physical assessment of a patient with pleural effusion involves examining breath sounds, chest expansion, tracheal position, and vital signs. Diagnosis involves chest x-ray, CT scan, ultrasound and thoracentesis. 3. Treatment focuses on treating the underlying cause as well as draining fluid and preventing reaccumulation through procedures like thoracentesis, chest tubes, pleurodesis using chemical agents or surgery.