Patients in hemorrhagic shock can be observed to have a reduced pulmonary artery wedge pressure (PCWP) by central manometry. Hemorrhagic shock is commonly associated with bleeding caused by trauma, bleeding from peptic ulcers, ruptured esophageal varices, and bleeding caused by obstetrical and gynecological diseases. Whether shock occurs after blood loss depends not only on the amount of blood loss, but also on the rate of blood loss. Shock often occurs in the case of rapid, massive (more than 30-35% of total blood volume) blood loss without timely replacement. Causes of reduced pulmonary artery wedge pressure (pcwp): Microcirculatory disorders (ischemia, bruising, disseminated intravascular coagulation) lead to inadequate perfusion of arterial blood in the microcirculation and functional and metabolic impairment of vital organs due to hypoxia, which is a common rule for all types of shock. The changes of microcirculation during shock can be roughly divided into three phases, namely, microcirculatory ischemic phase, microcirculatory stasis phase and microcirculatory coagulation phase. The microcirculatory ischemic phase (ischemic hypoxic phase) is characterized by the following changes in the microcirculation: 1. contraction of the microartery, posterior microartery and precapillary sphincter, a sharp decrease in microcirculatory perfusion and a decrease in pressure. 2.Microvenules and small veins are less sensitive to catecholamines and contract less. 3, The arteriovenous anastomotic branch may have different degrees of opening, and blood flows directly from the microartery to the small veins via the arteriovenous anastomotic branch. The key change causing microcirculatory ischemia is the strong excitation of the sympathetic-adrenomedullary system. Different types of shock can cause sympathetic-adrenomedullary shock by different mechanisms and in cardiogenic shock, reduced cardiac output and lower arterial blood pressure can excite the sympathetic-adrenomedullary system through the sinus arch reflex, and in most endotoxic shock In most cases of endotoxic shock, endotoxin can directly excite the sympatho-adrenomedullary system.