The development of pleural effusion after 4 months of bed rest in the elderly may be related to increased vascular hydrostatic pressure, lymphatic return dysfunction, and increased vascular permeability. It can be treated by puncture therapy, surgical therapy, drug therapy and so on. 1. Increased vascular hydrostatic pressure: mainly refers to the imbalance of pressure inside and outside the blood vessels, which makes the fluid inside the blood vessels enter into the thoracic cavity, and is usually seen in constrictive pericarditis, etc., thus causing pleural effusion. Pleural fluid can be extracted by thoracentesis to improve the symptoms. 2. Lymphatic reflux dysfunction: malignant tumors can block the lymphatic vessels, so that the reflux of fluid in the thoracic cavity is obstructed, which can cause pleural effusion. It can be treated by closed thoracic drainage surgery or even lymphatic vessel ligation. 3. Increased vascular permeability: Increased vascular permeability can cause vascular fluid to enter the chest cavity, which is common in diseases such as pneumonia. It can be treated by taking medicines to fight infection, such as levofloxacin tablets and cefixime granules. It is recommended that patients go to the hospital in time, please ask the doctor to clarify the cause of the disease and then correctly treated, specific drugs need to be used under the guidance of the doctor.