Management of Fluid and Electrolyte problems in Children

Hypernatraemia is defined as a plasma sodium greater than 150 mmol/l. It is not a specific disease and a cause should be sought.

There is an increase in the amount of sodium relative to water and hypernatraemia usually leads to a decrease in ICF. The brain is most at risk.

Most people, if their thirst centre is intact, will take in electrolyte-free water (EFW) to correct the excessive loss of EFW.

Symptoms

• Mild confusion
• Thirst
• CNS dysfunction
• Polyuria

Urine osmolality can give a clue to the cause:

• Large volume of hypo-osmolar urine - diabetes insipidus
• Large volume of slightly hyper-osmolar urine - osmotic or pharmacologic diuresis
• Minimum volume of maximally hyper-osmolar urine - non-renal water loss without water intake

A rarer cause of hypernatraemia is a gain of sodium in excess of water. This will produce an increase in ECF volume.

Aetiology