The microcirculatory changes in the early phase of shock are as follows. In the early phase, the effective circulating blood volume decreases significantly, tissue perfusion is insufficient, cells are hypoxic, and circulating volume decreases, causing a decrease in arterial pressure. The pressure receptors in the aortic arch neck and aortic sinus in the body will stimulate the vascular center to have a hypotensive reflex. At this time, the patient will have an accelerated heart rate and increased cardiac output to maintain a relatively stable circulating volume, and the circulating blood volume will be redistributed by contracting the small vessels in the periphery and viscera to ensure the effective perfusion of the heart, brain and other important tissues. As the smooth muscles of small arteries and veins and the precapillary sphincter are affected by catecholamines and other factors, the arteriovenous short circuit may open up.