Mannitol should be ordered within 30 minutes. The main effect of mannitol is to cause the effect of lowering cranial pressure through its dehydration, which has a certain effect on acute hemorrhagic encephalopathy, acute cerebral edema, acute cerebral infarction or acute stroke. For patients with cervical or lumbar disc herniation, mannitol can also be applied to reduce nerve root edema and achieve pain relief. Mannitol should be administered as fast as possible, usually within 30 minutes, at about 100 drops/minute. Therefore, mannitol is fast and can have the effect of dehydration and lowering cranial pressure. However, there is one exception: patients with acute cardiac and renal impairment are not able to take large amounts of mannitol quickly.