The respiratory index (RI) is the ratio between the difference in alveolar arterial partial pressure of oxygen and arterial partial pressure of oxygen, calculated by the formula: P(A-a)DO2 /PaO2, and the normal reference range is less than or equal to 1.0. This index is an index that reacts to the ventilation function and oxygen exchange function of lung tissue, and is generally used for monitoring the vital signs of critically ill patients, for assessing the oxygenation function of respiratory failure, respiratory distress syndrome, acute pancreatitis, and for adjusting the parameters of the ventilator and the timing of its withdrawal. If the respiratory index is elevated, it suggests that the patient is hypoxic and has decreased oxygenation function. If the respiratory index is greater than 2, mechanical ventilation therapy is required. If the physical examination found that the respiratory index is abnormal, you need to consult a doctor in time, improve the relevant examination under the guidance of specialists to treat the cause.