Circulatory mechanism of pleural fluid: pleural fluid is due to pressure gradients from the body circulation vessels of the wall and dirty pleura through the leaking pleura into the pleural cavity, and then absorbed back through the lymphatic vessels micropores of the wall pleura via the lymphatic vessels (under normal circumstances the dirty pleura has a smaller role in the circulation of pleural fluid). The fluid hydrostatic pressure of the wall layer pleura is about 30cmH2O pleural cavity pressure is about -5cmH2O, its fluid hydrostatic pressure is equal to 30-(-5)=35; the opposite of fluid hydrostatic pressure is the plasma colloid osmotic pressure gradient, plasma colloid osmotic pressure is about 34cmH2O, pleural fluid contains a small amount of protein, its colloid osmotic pressure is about 5cmH2O, the resulting colloid osmotic pressure gradient is 34-5=29; fluid The difference between hydrostatic pressure and colloid osmotic pressure is 35-29=6. Pleural effusion: The pleural cavity is a negative pressure cavity located between the lung and the chest wall, under normal circumstances there is a thin fluid in the pleural cavity to play a lubricating role in respiratory movements, the fluid is in dynamic equilibrium, any factor that can make the formation of fluid in the pleural cavity too fast or absorption too slow can produce pleural effusion (pleural fluid). Mechanisms of pleural effusion: 1, increased hydrostatic pressure within the pleural capillaries; such as congestive heart failure, constrictive pericarditis, increased blood volume, and obstruction of the superior vena cava or umbilical vein. 2, decreased intrapleural capillary colloid osmotic pressure; such as hypoproteinemia, cirrhosis, nephrotic syndrome, acute glomerulonephritis, mucinous edema. 3, increased permeability of the pleura; such as pleural inflammation (tuberculosis, pneumonia), connective tissue disease (systemic lupus erythematosus, rheumatoid arthritis), pleural tumors (malignant metastases, mesothelioma), pulmonary infarction, subphrenic inflammation (subphrenic abscess, liver abscess, acute pancreatitis) 4, mural pleural lymphatic drainage obstruction; such as cancerous lymphatic duct obstruction, abnormal developmental lymphatic drainage. 5.Injury. Such as aortic aneurysm rupture, esophageal rupture, thoracic duct rupture, etc., producing hemothorax, thick chest celiac disease. Clinical manifestations: 1, symptoms, symptoms most commonly dyspnea, may be accompanied by chest pain and cough; tuberculous pleurisy is most often seen in young people often have fever, irritating dry cough, chest pain, etc. Malignant pleural effusion is mostly seen in middle-aged patients and above, usually without fever and vague chest pain, accompanied by wasting and symptoms of respiratory tract or primary tumor. Heart failure is mostly leaking fluid, often accompanied by symptoms of cardiac insufficiency. 2. Signs, related to the amount of fluid accumulation. A small amount may have no obvious signs, or may be palpable pleural friction (sound) medium to large amount of the affected side of the chest is full, palpable fibrillation is weakened, local percussion turbid sound, may be accompanied by the mediastinal displacement of the trachea to the healthy side. Laboratory tests The leakage fluid is clear and bright, does not coagulate at rest, specific gravity <1.016~1.018, cell count less than 100*10^6/L is dominated by lymphocytes and mesothelial cells, low protein content (<30g/L) is dominated by albumin, mucin test is negative; exudate is multi-colored, straw yellow is common, specific gravity >1.018, leukocyte count often exceeds 500*10^6/L, protein content is high. 6/L, high protein content (>30g/L) pleural fluid/serum ratio >0.5. Light criteria: especially for those with protein concentration in the range of 25-35g/L, any of the following can be diagnosed as exudate, 1. pleural fluid/serum bilirubin ratio >0.5; 2. pleural fluid/serum LDH ratio >0.6; 3. pleural fluid LDH level greater than serum normal value In addition, there are pleural effusion cholesterol concentration >1.56 mmol/L, pleural effusion/serum bilirubin ratio >0.6, and serum-pleural effusion albumin gradient <12 g/L. Difficulty in distinguishing the nature of pleural effusion is seen in the case of malignant pleural effusion. X-rays Changes are associated with the volume of effusion and the presence of encapsulation or adhesions. Very small amount of free effusion less than 300ml, the angle of rib diaphragm is blunted, sometimes it needs to be distinguished from pleural adhesions by lying on the affected side, when the amount increases it shows an arc-shaped shadow of high external and low internal, lying flat is the increased density of the affected lung field.