Dehydration can be classified as hypotonic, hypertonic and isotonic dehydration according to the changes in blood sodium concentration and blood osmolarity. Hypertonic dehydration is usually more common in daily life and can be classified as mild, moderate or severe according to the grade. In mild dehydration, the most prominent manifestation is thirst, but there is usually no other feeling, and the amount of dehydration is 2%-4% of body weight. In moderate dehydration, the water deficiency is 4%-6% of body weight, and the patient will be extremely thirsty, and have dry mouth, dry tongue, deep sunken eyes, general weakness, and loss of skin elasticity, which is not dangerous if the patient can rehydrate in time. If the water deficiency is greater than 6% of body weight, the patient can show all the above symptoms, but also mental symptoms such as mania and hallucinations, which can be life-threatening if not rescued in time. It is recommended that patients should pay attention to hydration in their daily life, and if there is a large loss of water due to the corresponding disease, they should go to a regular hospital for intravenous rehydration in time.