Central venous pressure (CVP) is the pressure at the point where the superior and inferior vena cava enters the right atrium, measured by the superior and inferior vena cava or the built-in tube of the right atrium, which reflects the right atrial pressure and is one of the main indicators of clinical observation of hemodynamics, which is influenced by three factors: right heart pumping function, circulating blood volume and vascular tension of the venous system of body circulation. The measurement of CVP is important to understand the effective circulating blood volume and right heart function. The normal value is 0.49-1.18 Kpa (5-12 cmH2O). Central venous hypotension refers to the right atrium and large intra-thoracic veins with blood pressure less than the normal value of 0.49-1.18 Kpa (5-12 cmH2O). Differential diagnosis of low central venous pressure Increased venous return The central venous pressure increases when the venous return rate increases. Therefore, central venous pressure may be elevated in the presence of increased blood volume, systemic venous constriction, or increased peripheral venous pressure due to microarterial diastole. A higher-than-normal central venous pressure with a tendency to progressively increase is indicative of rapid infusion or cardiac ejection insufficiency. The measured central venous pressure is less than the normal value of 0.49 kPa The blood pressure in the right atrium and large veins in the thorax is called the central venous pressure. The level of central venous pressure depends on the interrelationship between the ejection capacity of the heart and the amount of venous blood returned to the heart. If the heart has a high ejection capacity and is able to eject the blood returning to the heart into the arteries in a timely manner, the central venous pressure will be lower. Central venous pressure is another indicator of cardiovascular function. Clinically, when treating shock with infusion, besides observing the change of arterial blood pressure, we also need to observe the change of central venous pressure. The normal range of central venous pressure is 4-12cmH2O, if the central venous pressure is low or has a tendency to decrease, it often indicates that the amount of infusion is insufficient.