Low serum carbon dioxide is related to respiration and metabolism, low carbon dioxide in the serum reflects low carbon dioxide binding in the blood. 1, respiratory factors include high fever, improper use of ventilators, and bronchial asthma and other lung diseases, these diseases will lead to fast respiratory rate, the relative growth of expiratory time, longer inspiratory time, hyperventilation, resulting in excessive carbon dioxide in the exhaled gas, resulting in lower carbon dioxide in the body. This situation requires the use of mask oxygen to delay the discharge of carbon dioxide; 2. Metabolic factors, commonly seen in diarrhea, vomiting and diarrhea, frequent vomiting can easily lead to excessive loss of acid in the body, thus causing metabolic alkalosis and a decrease in carbon dioxide binding power, which can be treated symptomatically by supplemental fluids, antiemetic and antidiarrheal.