Mannitol has the following functions: 1, tissue dehydration, used to treat cerebral edema caused by various reasons, reduce intracranial pressure, prevent brain herniation; 2, mannitol can effectively reduce intraocular pressure, applied when other intraocular pressure reduction is ineffective or intraocular surgery preparation; 3, osmotic diuretic, used to identify prerenal factors or acute renal failure caused by oliguria, can also be used to prevent various causes of acute 4, as an auxiliary diuretic measure for the treatment of nephrotic syndrome, cirrhosis, ascites, especially when accompanied by hypoproteinemia; 5, for certain drugs or toxic poisoning, this drug can promote the excretion of the above substances and prevent nephrotoxicity; 6, can be used as a flushing agent for transurethral resection of the prostate; 7, preoperative intestinal preparation. Side effects of mannitol include: 1, water and electrolyte disorders are most common, often due to large amounts of rapid intravenous injection of mannitol. The simultaneous rapid and massive increase in blood volume causes acute and chronic renal failure, especially chronic renal failure, leading to heart failure, dilutional hyponatremia, and occasionally can lead to hyperkalemia; 2. Inappropriate excessive diuresis, leading to a decrease in blood volume and aggravating oliguria; 3. The transfer of large amounts of intracellular fluid to extracellular fluid can also lead to tissue dehydration and cause central nervous system symptoms.