The causes of pleural effusion are divided into two types, systemic diseases and local diseases. Systemic diseases include: 1, pleural effusion caused by heart failure in patients, pleural effusion caused by abnormal liver function or poor nutrition and low albumin; 2, connective tissue diseases, such as systemic lupus erythematosus; 3, drugs taken by patients, such as amiodarone, a drug often used for heart disease, chemotherapy drugs, or phenytoin sodium for epilepsy and furantoin for urinary tract infections, can cause pleural effusion. Betalactam for hypertension can also cause pleural effusion; 4. Exposure to asbestos in life can also cause pleural effusion; 5. Other diseases including tuberculosis and lung cancer, the most common tumor in elderly patients, can cause large pleural effusions. Large pleural effusion can also be caused by other sources of fluid such as esophageal rupture, or lymphatic leakage, or the accumulation of fluid in the chest cavity.