Hyponatremia and Hypernatremia

Serum sodium is a concentration, not a direct measure of the body’s total sodium stores. It mainly tells you how much water is present relative to extracellular sodium. A low result may reflect water excess, sodium loss, or both; a high result usually reflects water loss that exceeds sodium loss. The number becomes clinically urgent when it is paired with a rapid change or neurologic findings. Water moving into brain cells produces headache, nausea, confusion, seizures, and reduced level of consciousness in hyponatremia. Water leaving brain cells produces thirst, irritability, weakness, confusion, and seizures in hypernatremia. Treatment therefore has two goals: correct the underlying water imbalance and control the rate of correction so that treatment does not create a second brain injury.