The normal value of partial pressure of carbon dioxide in arterial blood is 36-44 mmHg, and the normal value of partial pressure of carbon dioxide in venous blood is 45-55 mmHg. The partial pressure of carbon dioxide refers to the pressure generated by the carbon dioxide dissolved in blood, which can directly reflect the body’s respiratory function because of the strong diffusion ability of carbon dioxide in blood, and is mainly used to respond to the phenomenon of hypoxia in body tissues. The partial pressure of carbon dioxide plays an important regulatory role in human metabolism, such as regulating the acid-base metabolic balance in the body. The arteriovenous partial pressure difference of carbon dioxide is the difference between the arterial partial pressure of carbon dioxide and the central venous partial pressure of carbon dioxide, which is a sensitive indicator of blood flow in the body, and is used to evaluate whether the tissues have sufficient blood flow to remove the carbon dioxide accumulated in the tissues, but cannot be used to evaluate whether the tissues are hypoxic, as follows: 1. When the partial pressure difference between arteriovenous carbon dioxide is greater than 6 mmHg, it indicates that the cardiac output is insufficient, and increasing the cardiac output can relieve tissue hypoxia.