Pulmonary edema refers to the imbalance of the production and reflux of tissue fluid in the lungs caused by some reasons, so that a large amount of tissue fluid cannot be absorbed by the pulmonary lymphatics and pulmonary venous system in a very short time, and it infiltrates from the pulmonary capillaries and accumulates in the alveoli, pulmonary interstitium and small bronchi, thus causing serious obstruction of pulmonary ventilation and gas exchange function. Clinically, it manifests as extreme dyspnea, sitting breathing, cyanosis, sweating, paroxysmal cough with a large amount of white or pink foamy sputum, symmetrical moist rales in both lungs, and butterfly-shaped flake-like blurred shadows in both lungs can be seen in the chest X-ray. Shock or even death may occur in the late stage. Arterial blood gas analysis may show low O2, low CO2 partial pressure, severe lack of O2, CO2 retention and mixed acidosis in the early stage, which is one of the clinical critical diseases.