Central hyponatremia includes cerebral salt depletion syndrome (CSWS) and syndrome of inappropriate secretion of antidiuretic hormone (SIADH), which have similar clinical manifestations and are difficult to distinguish by traditional diagnostic criteria. 1. Data and methods Diagnostic criteria: (1) presence of central nervous system disease; (2) serum sodium <130 mmol/l; (3) urine sodium >20 mmol/L or >80 mmol/L for 24 h, urine osmolality >plasma osmolality; (4) urine volume >1800 ml/d; (5) hypovolemia; (6) systemic dehydration manifestations (dry skin, sunken eyes, decreased blood pressure etc.). 2. Clinical manifestations The patient’s condition worsened, mental abnormalities, coma or coma deepened 1-12 d after injury or surgery. No delayed intracranial hemorrhage was found on repeat CT examination, and brain swelling or cerebral edema was mostly seen. Laboratory tests showed significant hyponatremia, with abnormally high urinary sodium values > blood sodium values. When the blood sodium decreases further, convulsions, paralysis or even death may occur. The patient’s heart rate was >110 beats/min, blood pressure was 12-13/6-8kPa, 24h urine volume was >3000, blood sodium was 101-123mmol/L; blood chloride was 73-87mmol/L; plasma osmolality was 216-2547mmol/kg; urine sodium was 70-78mmol/L; urine specific gravity was 1.010-1.015. Blood volume was decreased. Weight loss and obvious signs of dehydration. 3, treatment method hyponatremic patients diagnosed as CSWS immediately after the full sodium, rehydration treatment, first according to the formula to calculate the need to supplement the total amount of sodium (mmol): [blood sodium normal value 142 (mmol / L)] a [blood sodium measured value (mmol / L)] × weight (kg) × 0.6 (0.5 for women), the first day to replenish about 2 / 3 sodium deficit and the daily requirement 4.5g, of which the missing amount was replenished with 3% NaCl hypertonic solution in 2-3 times within 24h, the rest was replenished with isotonic solution, and the full amount of sodium was replenished according to the sodium deficit on the second day. Some severe craniocerebral injury combined with different degrees of urinary collapse, the maximum daily urine volume up to 7000ml, in the sodium supplementation at the same time according to the volume of urine to fully replenish the lost fluid, adults more than 200ml per hour urine volume with the addition of posterior pituitary hormone. During treatment, 24h water intake and output, blood biochemistry, etc. were monitored daily. Central hyponatremia is one of the common complications in neurosurgical patients, which can occur in craniocerebral injury (especially heavy craniocerebral injury), SIADH and CSWS, and CSWS is more common. SIADH is a result of central nervous system damage that stimulates excitation of the hypothalamic-pituitary axis, causing excessive release of antidiuretic hormone and water retention, leading to hypervolemic hyponatremia. siadh is also commonly seen in central nervous system disorders, and with CSWS both present with serum sodium <130 mmol/l as well as increased urinary sodium. According to the diagnostic criteria proposed by palmer et al: (1) serum sodium <130 mmol/l; (2) urinary sodium >20 mmol/L or >80 mmol/L for 24 h; (3) urinary osmolality > blood osmolality; (4) central venous pressure >12 cmH2O; (5) blood urea nitrogen, creatinine and albumin concentrations at or below the low limit of normal; (6) erythrocyte pressure product < 0.35; and (7) peripheral edema. The main differentiation between the two is that patients with csws have decreased central venous pressure, the presence of hypovolemia, marked signs of dehydration and persistently elevated urinary sodium; patients with siadh have increased central venous pressure, increased blood volume, no signs of dehydration and early elevation and late decrease in urinary sodium. The differential diagnosis between the two is quite important because the treatment is completely opposite, with siadh patients treated with water restriction, while csws patients are treated with the aim of timely sodium and water supplementation, correction of hyponatremia and hypovolemia, and improvement of cerebral perfusion pressure and cerebral blood supply and oxygenation. Once the diagnosis of cerebral salt depletion syndrome is confirmed, high concentration sodium chloride solution should be supplemented according to daily blood biochemical results to maintain water and electrolyte balance, while paying attention to potassium supplementation and correction of acid-base balance, and the blood sodium of most patients can be normalized in about 2 weeks after treatment. It should be noted that although too slow a correction of hyponatremia may increase the rate of disability or death, too fast a treatment may be accompanied by CPM (central pontine demyelination), which manifests as insidious limb flaccidity, altered consciousness, cerebral nerve abnormalities and pseudomyelinating palsy. Therefore, too rapid adjustment of blood sodium should be avoided, and electrolytes, urine sodium and 24h urine volume should be closely monitored daily during the treatment.