Introduction

The normal range of the serum or plasma sodium concentration is 135 to 145 mmol/L.¹

Hypernatraemia (serum sodium concentration higher than 145 mmol/L) generally reflects water depletion. This is usually due to excess water loss from skin, gastrointestinal tract, lungs or kidneys, without adequate water intake (see common causes in Common causes of hypernatraemia). Inadequate water intake is an important cause of hypernatraemia in very young and very old people. Hypernatraemia may also result from enteral or parenteral feeding of patients. Patients with diabetes insipidus may develop hypernatraemia rapidly if access to water is restricted and desmopressin therapy is withheld. A rare cause of hypernatraemia is a lack of thirst caused by a hypothalamic lesion. Patients with hypernatraemia may develop lethargy, confusion and coma, due to depletion of intracerebral fluid.

Sodium phosphate laxatives should be used with caution because they may cause major fluid and electrolyte disturbances (including hypernatraemia), especially in older people.