Red fluid drawn from the lungs may be caused by blood oozing out after trauma, resulting in bloody pleural effusion, or bloody pleural effusion after chest surgery, or malignant tumor involving the pleura, resulting in bloody pleural effusion. 1. Caused by trauma: after chest trauma, the blood vessels of lungs or chest wall and intercostal blood vessels bleed, and the fluid accumulates in the chest cavity, resulting in red fluid accumulation, which requires active thoracoscopic exploration or thoracotomy surgery. 2. Caused by postoperative: after surgery, the patient’s chest tube is removed too early, and some of the fluid is retained, which will draw out red fluid. In this case, thoracentesis or ultrasound-guided thoracentesis and aspiration is feasible to draw out the fluid in the thoracic cavity to relieve the clinical symptoms of chest tightness and shortness of breath. 3. Caused by malignant tumors: malignant tumors, pleural metastasis, producing obvious effusion. Chemical pleural fixation, intrathoracic injection of antitumor drugs such as injectable actinomycin D, injectable epirubicin hydrochloride, or pleural adhesion agents can be chosen to slow down the production of pleural fluid. Appearance of this situation is recommended to timely to the blood routine, blood sedimentation, chest X-ray and other tests, to see exactly which disease is caused by a clear diagnosis before treatment, do not self-medication.