The central veins are the superior and inferior vena cava, and of greatest clinical relevance, are the central venous pressure and the central venous catheter. By central venous pressure, we mean the pressure at the point where the superior and inferior vena cava enters the right atrium, which can be measured by a transducer in the central venous catheter or directly. Central venous pressure can objectively reflect the preload of the right ventricle and can effectively monitor the amount of circulating blood, which is important for hemodynamic monitoring and is an important reference indicator for the amount of blood and fluid transfusion in clinical practice. Central venous cannulation, which is a catheter placed in the central vein, is one of the measures frequently used in various severe cardiac insufficiency, severe shock, severe trauma, major surgery, extracorporeal circulation surgery and resuscitation of patients. In addition, central venous catheters are often placed in patients who require long-term intravenous nutrition, long-term infusions, and large amounts of rapid infusions, through which medications, blood draws, laboratory tests, and other treatments are administered.