Low total carbon dioxide may be due to respiratory alkalosis or metabolic acidosis. The etiology of metabolic acidosis includes excessive direct loss of bicarbonate, dysfunction of renal acid excretion and alkalinity preservation, etc. The etiology of respiratory alkalosis includes hypoxemia and pulmonary disorders, direct stimulation of the respiratory center, and vigorous metabolism of the body. 1. Metabolic acidosis: (1) Dysfunction of renal acid-excretion and alkali-preservation: if one suffers from severe renal failure, the fixed acid in the body cannot be excreted from the urine, leading to an increase in the concentration of hydrogen ions, which causes excitation of the respiratory center and changes the pulmonary ventilation to compensate for it, making the carbon dioxide low. (2) The direct loss of bicarbonate is too much: severe diarrhea, intestinal fistula can cause a large loss of bicarbonate. The body compensates by making the carbon dioxide low. 2. Respiratory alkalosis: (1) hypoxemia and pulmonary disease: patients with cardiopulmonary disease can stimulate respiratory movement due to hypoxia to increase carbon dioxide excretion. (2) Direct stimulation of the respiratory center: central nervous system diseases such as cerebrovascular disorders and brain tumors can stimulate the respiratory center and cause hyperventilation. (3) Exuberant metabolism of the body: seen in high fever, hyperthyroidism, etc., hypercatabolism of the body stimulates the respiratory center to be excited and hyperventilate. If you find low carbon dioxide, it is recommended that you consult a doctor for timely examination and treatment, so as not to delay your condition.