Weakness, nausea and vomiting, headache, anorexia, muscle twitching, drowsiness, and even coma are often seen in the elderly. It is often mistakenly thought to be caused by aging or aggravation of a primary disease and thus ignored, with serious consequences. One of the common causes of this condition is low blood sodium, or hyponatremia. What is hyponatremia? Hyponatremia is defined as a blood sodium level below 135 mmol/L. Hyponatremia is divided into three categories: isotonic, hypertonic, and hypotonic. The third category is most common in the elderly. Common causes: 1. Decreased sodium-retaining function of the kidney in the elderly; 2. Inadequate sodium intake due to loss of appetite; 3. Loss of digestive juices due to vomiting, diarrhea, pancreatic fistula and biliary fistula; 4. Inappropriate use of drugs, such as cyclophosphamide and diuretics; 5. Heart failure, cirrhosis, nephrotic syndrome, and severe renal insufficiency. Clinical symptoms If hyponatremia occurs within 24 hours (i.e., acute hyponatremia), or if the degree of sodium drop is severe (i.e., below 120 mmol/L), it manifests as nausea, vomiting, headache, muscle cramps, convulsions, coma, seizures, and even death. If hyponatremia occurs slowly or is not severe, there are usually no obvious symptoms, or only non-specific manifestations such as nausea, decreased appetite, fatigue, anxiety, etc., which are often misdiagnosed. Prevention Elderly people should not overly restrict sodium diet due to decreased appetite, and should eat more. In addition, drugs should be used carefully and reasonably to treat the primary disease. At the same time, care should be taken not to cause a rapid rise in blood sodium in a short period of time during the treatment of hyponatremia to avoid further electrolyte disorders.