1, the pharmacological mechanism and characteristics of mannitol and side effects The hypotensive effect of mannitol is not only a simple diuretic, but also mainly lies in causing an increase in blood osmolarity, which causes water inhalation from brain tissue into the blood, thus reducing cerebral edema and lowering intracranial pressure. Generally, it takes effect within 20 minutes after intravenous injection, and the hypotensive effect reaches its peak in 2-3 hours and can be maintained for 4-6 hours. The commonly used dose is 0.25-0.5g/kg.once for adults. However, years of clinical practice has proved that mannitol can cause hypokalemia, induce or aggravate heart failure, hematuria, renal insufficiency, renal failure, etc. 2, the mechanism of action and timing of mannitol in cerebral hemorrhage 1) After admission to the hospital, if there is no severe cranial hypertension and the vital signs are stable, sedation, diuresis and blood pressure stabilization should be taken after the first CT examination (several recent international studies have confirmed that maintaining systolic blood pressure at 140-180 mmhg is safe; the lower the blood pressure in this range, the better it is for hemostasis), in order to reduce the risk of rebleeding. At the same time, the patient’s vital signs were kept stable and the changes in intracranial pressure were closely monitored. If the condition and the size of the hematoma are stable, and there is still no manifestation of cranial hypertension and the vital signs are stable, continue to observe and continue to monitor the changes of intracranial pressure; if there is manifestation of cranial hypertension such as headache, osmotic drugs such as mannitol can be used to help reduce brain tissue edema and alleviate the symptoms. (2) If pre-cerebral herniation manifestation such as deepening of consciousness occurs during the observation period within 6h of onset, CT should be reviewed and brain surgery consultation should be requested in a timely manner. (3) If severe cranial hypertension appears after admission and requires surgery, regardless of the time of onset, high-dose mannitol and other osmotic drugs should be applied immediately to reduce intracranial pressure to buy time for surgery. 3.The choice of treatment plan in case of cerebral hemorrhage The treatment plan should be decided according to the site of bleeding and the amount of bleeding. 4.Drop rate is generally required to be finished within 20min. It depends on the different conditions of each patient. 5.Dosage problem The dosage of small amount of dehydration and lowering cranial pressure is small, and the dosage of large amount and fast drip rate will increase the side effects accordingly. It should be treated carefully according to the specific situation of the patient. 6, the rebound mechanism of mannitol and preventive measures intracranial hypertension patients with sedation mannitol lowering cerebral pressure, the dose to 400mg/kg, the input rate should not exceed 50mg/(kg?min) is appropriate, so as to achieve the best antihypertensive effect, but also to prevent cerebral pressure rebound.