When an arterial blood draw is performed, it is usually for a blood gas analysis test. Because blood gas analysis needs to look at the partial pressure of oxygen in the blood, and the partial pressure of oxygen in arterial blood is completely different from that in venous blood. Normally, the partial pressure of oxygen in arterial blood can reach 90 mmHg or more, while the partial pressure of oxygen in venous blood is 30-40 mmHg, so arterial blood is drawn to determine the level of partial pressure of oxygen in the blood and thus assess the oxygen level in the body. This test is mostly used for patients with respiratory diseases to assess the severity of the respiratory disease and the treatment regression by monitoring the oxygen partial pressure level in the body. In addition to monitoring the partial pressure of oxygen in the blood, blood gas analysis can also calculate the carbon dioxide binding capacity of the blood, the partial pressure of carbon dioxide, the acid-base environment of the body and the electrolyte level.