Both crystalloid and colloid fluids can be used for rehydration of the body. Crystalloid fluids are mixed solutions of sodium chloride and other electrolytes, and colloid fluids are macromolecular solutions that maintain osmolality in blood vessels. 1. Crystalline solution: it is a mixed solution of sodium chloride and other electrolytes, such as 0.9% saline. It has the characteristics of low viscosity and can be input more quickly, which has high clinical value for hypovolemic patients who need to replenish blood volume as soon as possible. Crystalline solutions also mobilize some fluid from the tissues into the blood vessels, increasing blood volume. At the same time also through the receptor reflex excitation of the cardiovascular system, to help maintain hemodynamic stability, but it belongs to the vasodilator, so the input speed should not be too fast. 2. colloidal fluid: it is the high molecular weight solution that maintains osmotic pressure in the blood vessel, and the diameter of its solute molecule is larger than 1nm. it can be divided into natural colloidal fluid and artificial colloidal fluid. Colloid fluid is better than crystalloid fluid in restoring and maintaining blood volume, and the incidence of nausea and vomiting and diplopia after input is lower. When rehydration fluid is needed, it should be selected under the guidance of a doctor, and should not be used blindly.