When blood is drawn for arterial blood gas analysis, it is sometimes drawn as venous blood. The difference in appearance is that arterial blood is usually bright red in color, and you can see the fluid pulsating inside the syringe when drawing arterial blood. Venous blood is dark red in color, and the pulsation of the fluid is not visible when the blood is drawn. If the patient has severe hypoxia and low blood pressure, it is difficult to distinguish arterial blood or venous blood from the appearance. In this case, it is also possible to distinguish from the blood gas analysis results by looking at the oxygen saturation and partial pressure of oxygen combined with the finger pulse oxygen shown on the patient’s ECG monitor to determine whether the blood is arterial or venous. It is not possible to distinguish arterial blood from venous blood by looking at the PH and partial pressure of carbon dioxide results. Usually the partial pressure of arterial blood is 60mmHg for 90% pulse oximetry, 50mmHg for 80% pulse oximetry, and 40mmHg for 70% pulse oximetry, and the difference between pulse oximetry and oxygen saturation is more than 5%, while arterial blood is considered to be drawn within 5%.