Very low urinary sodium excretion is a significant clinical manifestation of hyponatremia. The normal value of blood sodium is 142 mmol/L (135-145 mmol/L), and blood sodium below 135 mmol/L is considered hyponatremia. Urinary sodium volume: 70-90 mmol/24h in normal adults, which is approximately 4.1-5.3 g of sodium chloride. if urinary Na+. The severity of hyponatremia depends on the rate of blood [Na ] and blood sodium decline, blood [Na ] above 125mmol/L rarely causes symptoms; [Na ] between 125 and 130mmol/L, also only gastrointestinal symptoms, at this time the main symptoms are weakness, nausea and vomiting, headache and sleep, painful muscle spasms, neuropsychiatric symptoms and reversible ataxia, etc. In In the early stage of hyponatremia, brain cells have adaptive regulation to the imbalance of intra- and extracellular osmolarity. Within 1 to 3 h, extracellular fluid in the brain moves into the cerebrospinal fluid, and then returns to the body circulation. If hyponatremia persists, the adaptive regulation of brain cells is to throw away intracellular organic osmotic solutes including phosphate, creatine, inositol and amino acids (e.g. alanine, aminoethanesulfonic acid) to reduce cellular edema. If hyponatremia occurs within 48 h, there is a great risk of permanent neurological damage, and in chronic hyponatremia, there is a risk of osmotic demyelination, especially when hyponatremia is corrected excessively or too quickly. In addition to the clinical manifestations of cerebral cell edema and cranial hypertension, low blood pressure, fine pulse rate and circulatory failure may occur due to blood volume shrinkage, along with signs of water loss, while hyponatremia with normal overall sodium has no clinical manifestations of cerebral edema.