Dehydrating agents are commonly used in neurology, but improper use is also the most common therapeutic error, and many clinicians do not know how to properly view and use dehydrating agents. When using dehydrating agents, it must be clearly understood that: 1. Hypertonic dehydration can only dehydrate brain tissue with intact blood-brain barrier, but not lesioned brain tissue, because the blood-brain barrier is destroyed and no osmotic pressure difference can be formed between the brain and blood vessels. 2. Hypertonic dehydration can only be applied short-term or temporarily, or used for the treatment and prevention of brain herniation, but not for long-term treatment. The general course of treatment is 4-10 days. Hypertonic dehydration has different degrees of rebound phenomenon, and should be used with caution for the elderly, especially for patients with circulatory insufficiency, in order to avoid pulmonary edema and heart failure. Zhang Ning, Department of Neurosurgery, The First Affiliated Hospital of Baotou Medical College