Acute lung injury is an acute episode of lung injury caused by a variety of causes, including inflammation of the lung itself, occupational lesions, and trauma. Its most common clinical manifestation is acute respiratory distress syndrome, which causes respiratory failure. The diagnostic criteria are partial pressure of oxygen below 60 mmHg and partial pressure of carbon dioxide greater than 50 mmHg. The severity of acute lung injury is clinically determined by the oxygenation index, which is primarily a quantitative partial pressure of oxygen divided by the concentration of oxygen absorbed. The normal value of oxygenation index is between 200-300mmHg. If the oxygenation index is between 100-200mmHg, it belongs to mild acute lung injury. If it is below 100mmHg, it is severe acute lung injury, and the middle value belongs to moderate acute lung injury.