Algorithm for determining the cause of the Hypernatremia

Hypernatremia is defined as a serum sodium > 145 mEq/L

- hypernatremia can be due to:-

* net loss of water and sodium from the body with inadequate water replacement (commonest cause)
* inadequate water intake
* increased water loss from the body
* increased sodium load

- hypernatremia most commonly results from a net loss of water and sodium from the body coupled with inadequate water intake

- the hypotonic fluid loss can be due to renal (osmotic diuresis or diuretics) or extra-renal (skin or GIT) causes

Inadequate water intake is a universal prerequisite for the evolution of hypernatremia

(* hypernatremia due to indequate water intake is rarely seen in alert patients with a normal thirst mechanism + access to water + an ability to obtain and drink water)