Sodium Imbalance

Sodium is the major extracellular cation, but the serum sodium value is primarily a measure of the relationship between sodium and water. A low result does not automatically mean that the patient has lost sodium; excess water can dilute the sodium concentration. A high result usually reflects too little water relative to sodium, although sodium gain can also be responsible. Hyponatremia is a serum sodium concentration below 135 mmol/L: - Mild: 130–134 mmol/L - Moderate: 125–129 mmol/L - Severe: below 125 mmol/L Hypernatremia is a serum sodium concentration above 145 mmol/L. Mild hypernatremia is 146–149 mmol/L, while severe hypernatremia is above 158 mmol/L. The brain is the organ that makes a rapidly changing sodium concentration dangerous. In hyponatremia, water enters brain cells and can produce cerebral oedema. In hypernatremia, water leaves cells, causing cellular dehydration and brain shrinkage. The speed of change matters: acute hyponatremia develops in less than 48 hours and may cause abrupt neurological deterioration, while chronic hyponatremia persists for 48 hours or longer and may have subtle findings because the brain has partially adapted. That adaptation creates...