As a national essential drug included in the Chinese Pharmacopoeia, 20% mannitol injection is widely used in clinical practice as a common and preferred drug for treating cerebral edema, lowering intracranial pressure, preventing and treating edema and ascites caused by acute renal failure and glaucoma, large burns, etc. It is especially important in the treatment of neurological diseases. Retrospectively summarize the use of mannitol in neurological diseases, put forward some misconceptions in clinical application, and talk about their own experience in the use of drugs. 1, the application of mannitol misconceptions: (1) as long as the consideration of intracranial lesions, the first to 20% mannitol static point. (2) Do not understand the intracranial pressure, mannitol dosage is too large. (3) The duration of mannitol use is too long. (4) Mannitol is ordered as quickly as possible. (5) When dehydrating, do not pay attention to the water-electrolyte balance and over-dehydrate. (6) Mannitol contains high sugar content, and intravenous drip can cause blood glucose to rise. As far as the current situation is concerned, whenever cerebral hemorrhage or cerebral infarction is suspected, most of the medical personnel in the field emergency will immediately apply 20% mannitol. In fact, the instructions for mannitol clearly state that it is contraindicated in cases of active intracranial hemorrhage (except for craniotomy). Unless there are signs of brain herniation, mannitol should not be used or used with caution during the first few hours. After mannitol dehydrates tissue other than the hematoma, it can increase the hematoma-brain tissue pressure gradient, which can contribute to hematoma expansion or exacerbate active bleeding. The incidence of hematoma enlargement was significantly higher in patients who started mannitol within 8 hours after spontaneous cerebral hemorrhage (85.7%) than in those who used mannitol after 8 hours (17.2%) [1].Clinical studies and animal studies by Hallenbeck et al. demonstrated the efficacy of mannitol in the treatment of acute cerebral infarction, but the degree of efficacy was not related to the degree of local cerebral blood flow and reduction of cerebral edema [2]. Mannitol is best applied under intracranial pressure monitoring, with adjustment of the medication. Intracranial pressure greater than 2.7 kpa is mostly used clinically as the threshold for the need for intracranial hypotensive therapy. The purpose of controlling the threshold of intracranial hypertension is to prevent the formation of brain herniation and to prevent the adverse consequences of excessive medical hypotension. Mannitol can cause renal tubular degeneration and blockage when used for too long, resulting in oliguria or azotemia; experimental evidence shows that renal damage can be seen within 96 hours of intravenous mannitol injection, and can cause osmotic nephropathy (also known as mannitol nephropathy) when a large amount of rapid static dosing [4]; mannitol can also enter the area of blood-brain barrier disruption, aggravating local cerebral edema; large doses, prolonged use or plasma osmolality exceeding 320 mmol/L can cause electrolyte disorders, renal failure, acidosis, etc. The input rate of mannitol should be 10ml/min to 15ml/min, and the amount should be adjusted according to individual conditions. If the rate of mannitol input is too fast, the blood volume increases dramatically within a short period of time, causing a transient increase in blood pressure, resulting in headache and blurred vision, as well as acute renal impairment due to renal vasoconstriction and decrease in glomerular filtration rate [5]. Mannitol is a crystalline sugar alcohol with a sweetness equivalent to 57% to 72% of sucrose, easily soluble in water, alkaline in aqueous solution, not oxidized in air, metabolized in the body independently of insulin in the body, not a suitable substrate for oral microbial action without causing dental caries. Mannitol, as a dehydrating agent and osmotic diuretic, does not lead to increased blood glucose in clinical application and can be used as a sweetener for diabetic patients, obese people and for anti-caries [6]. Clinical experience with mannitol: 20% mannitol has a fast and strong dehydrating effect and a long duration of action. Intracranial pressure begins to fall within 10min-20min after injection and drops to the lowest level in 0.5h, which can reduce intracranial pressure by 50%-90%. About 1h later, the intracranial pressure starts to rise, and about 4h~8h, it will rise to the pre-drug level. General dosage: 1g/kg.d～2g/kg.d, 0.25g/time～0.5g/time, 3 times/d～4 times/d. The input rate is 10ml/min～15ml/min. Note: If mannitol is administered too quickly, the blood volume will increase dramatically within a short period of time, causing heart failure or pulmonary edema due to excessive circulatory load, causing transient blood pressure increase, renal vasoconstriction and decrease in glomerular filtration rate, resulting in acute renal impairment, especially in children and the elderly. The addition of aminophylline and vitamin C to mannitol can improve the therapeutic effect and reduce the dosage. Use with caution in cases of progressive renal failure, pulmonary edema, active intracranial hemorrhage (except for craniotomy), and in combination with tachyphylaxis in the elderly and in heart failure. Pay attention to the water-electrolyte balance during application. Mannitol sedation requirements: When sedation is administered, the nurse must make timely rounds and closely observe the drip rate and changes in condition. For critically ill patients or those who require pressure drip, they must guard the bedside from the beginning to the end and report any abnormalities to the doctor in time. Mannitol must be applied without crystals, if there are crystals, they should be dissolved by heating before use. If crystals appear during the drip, they should be replaced in time to prevent the treatment from being affected. Because of the fast drip rate of mannitol, it is easy to stimulate local pain, and in serious cases, it can cause phlebitis, leading to hardening and occlusion of veins, therefore, it is necessary to change the injection site or use intravenous needle frequently. Mannitol clinical application guidance: It is best to adjust the medication under intracranial pressure monitoring. The normal intracranial pressure (ICP) is 0.7kpa~2.0kpa (5mmHg~15mmHg) in adults and 0.4kpa~1.0kpa (3.0mmHg~7.5mmHg) in children. Intracranial pressure greater than 2.7kpa is mostly used clinically as the threshold for the need of intracranial pressure-lowering treatment. Clinical significance of intracranial pressure (ICP) monitoring: ①Quantitative monitoring of intracranial pressure. ②To understand the volume compensatory capacity of intracranial pressure. ③Early detection of intracranial lesions and early treatment. ④Monitoring cerebral perfusion pressure (CPP) and cerebral blood flow (CBF): CPP=mean arterial pressure (MSAP)-mean intracranial pressure (MICP); CBF=CPP/CVR (cerebrovascular resistance). Normal CPP is 9.3 kpa to 12.0 kpa. when ICP > 5.3 kpa and CPP < 6.7 kpa, cerebrovascular autoregulation fails. When ICP approaches MSAP, intracranial blood flow almost stops and the patient may enter coma within 20 seconds and may enter vegetative survival or even death in 4 min to 8 min. ⑤ Direct the treatment. Adjust the dosage of dehydrating agents, vascular antispasmodics, etc. ⑥Improve therapeutic efficacy and reduce mortality. ⑦ Judging the prognosis. Clinical intracranial pressure simple judgment method: (1) acute intracranial hypertension, headache, nausea, jet-like vomiting, impaired consciousness may occur, but no optic papilledema, optic papilledema usually appears in acute intracranial hypertension 3d to 4d, peaking at 7d; Cushing syndrome: respiration, pulse slowdown, blood pressure increase, is the manifestation of moderate and severe intracranial hypertension. (2) After 10 min to 15 min of mannitol application, typical intracranial hypertension symptoms are significantly reduced or disappear, indicating that intracranial hypertension requires therapeutic intervention. (3) When typical intracranial hypertension appears before the next application of mannitol, and the effect of the last application is achieved after medication, it indicates that the medication interval is reasonable. (4) The patient's headache and other symptoms do not change significantly before and after medication, and the application is considered to be due to other causes. (5) In vascular headache, the headache can be relieved after the sedative mannitol, which is due to the volume expansion effect of mannitol and the increase of cerebral blood flow in a short period of time, but the duration of headache relief is short. (6) After mannitol is administered, the patient's headache worsens or deteriorates, and the symptoms are relieved with rehydration and head hypo-positioning, suggesting intracranial low pressure. Mannitol intravenous care problems and measures: (1) If there are changes such as pain and redness in the injected vein promptly take hot compresses or apply effective drugs to prevent phlebitis from occurring. (2) Avoid drug infiltration in subcutaneous tissue causing severe pain, edema or even necrosis. If the puncture site is found to have external infiltration, the puncture site should be replaced in time. If necessary, local closed injection of procaine is feasible. (3) Cardiac insufficiency and dehydration at least urinary patients, active intracranial hemorrhage is prohibited (except for craniotomy), because of the ability to cross the placental barrier, causing fetal tissue edema, so pregnant women are prohibited. (4) Large amounts and prolonged application may cause acute renal failure. It is necessary to observe and record urine properties and monitor renal function, and once obvious renal impairment occurs, switch to glycerol fructose and tachyphylaxis. Mannitol can cause electrolyte disorders due to rapid dehydration and diuresis. Monitor central venous pressure and electrolytes, and replenish body fluids and electrolytes in a timely manner. (5) It can affect the results of certain tests and increase bilirubin and creatinine, uric acid and phosphate, which should be fully recognized when analyzing test results. The use of mannitol in neurology patients is high, and the application of intravenous indwelling needle, central venipuncture and PICC puncture has greatly reduced the vascular puncture injury, while the selected vessels are thicker and the blood flow is faster, which reduces the incidence of phlebitis. Once the symptoms of phlebitis such as pain and redness of the injected vein appear, timely adoption of alcohol wet compress, 50% magnesium sulfate hot compress and mannitol warming input can control the symptoms of phlebitis, and if necessary, change the site and perform venipuncture. Infusion of mannitol, once the leakage occurs, need to deal with timely, can take 50% magnesium sulfate local wet compress, 0.01% phentolamine solution soaked gauze wet compress, scalding cream external compress and other measures, can improve microcirculation, eliminate edema, prevent tissue necrosis. If the extravasation is accompanied by local bruising, local closed injection of procaine can reduce the fragility of local blood vessels, thus reducing or preventing the extravasation of fluid and pain reaction, relieving vasospasm, improving the ischemic-hypoxic state, facilitating the absorption of exudate and reducing local injury. If the treatment is not timely, more than 24h can not be recovered. For local ischemia has occurred, the use of hot compresses is strictly prohibited, because hot compresses can make the local tissue temperature rise, accelerated metabolism, increased oxygen consumption, and aggravate tissue necrosis. The clinical incidence of acute renal failure caused by the standardized use of mannitol is not high. By observing and recording the volume and color of urine, monitoring urinary routine and renal function, renal function damage can be detected in time, maintaining water-electrolyte balance, combined with tachyzoites and glycerol fructose application, the prognosis is generally good. In case of severe renal impairment, continuous renal replacement therapy at bedside or hemodialysis treatment can improve renal function and enhance the treatment of primary brain disorders to improve the efficacy.