Principles of postoperative rehydration of appendicitis: first, according to the condition of the disease, the mode of surgery and gastrointestinal function to determine the total amount of rehydration; second, according to the general condition of the body, water and electrolytes, as well as liver and renal function and so on to determine the type of rehydration; third, rehydration is generally the first fast and then slow, the first salt and then sugar, the principle of replenishment of potassium in the urine; fourth, the rehydration fluid should include three components: cumulative loss, continued loss and physiological needs, the three quantities of the three components of rehydration fluid together;