Management of Hypernatraemia

Serum Na >146mmol/L may result from reduced water intake (dehydration) or from situations in which water loss exceeds sodium loss (e.g. watery diarrhoea).

Assessment / Monitoring

There are no specific clinical features of hypernatraemia. It is usually diagnosed incidentally on serum testing. Also check other biochemical indices such as renal failure, hyperglycaemia and hypercalcaemia.
Identify underlying cause of hypernatraemia. Consider measuring urine osmolality.
- Urine osmolality < plasma osmolality – look for diabetes insipidus
- Urine osmolality > plasma osmolality – look for osmotic diuresis / heatstroke, etc.
If patient is also hypovolaemic, then monitor urinary output and renal function.

General Management

Treat underlying cause once identified. This is as important as treatment of hypernatraemia.
Mild cases of hypernatraemia - replace missing body water with oral water (not electrolyte drinks) or glucose 5% IV.
Severe cases of hypernatraemia (e.g. Na >170mmol/L) – give glucose 5% IV unless the patient is volume depleted and hypotensive, in which case give sodium chloride 0.9% IV. It is important that the rate of reduction of serum Na does not occur more rapidly than about 10mmol/L per day.
- Reassess and record patient's blood results and clinical status every 8 hours. Recheck serum Na after 2 litres of fluid replacement, or after 8 hours at the latest.
- Patients should be handed over to the next shift to clarify monitoring and fluid requirements.
If diabetes is simultaneously present then BM monitoring is required, and if the blood glucose is >30mmol/L then follow Management of Hyperglycaemic Hyperosmolar State (HHS) guideline.
If cranial diabetes insipidus is present, refer to Cranial Diabetes Insipidus, Inpatient Management guideline.
In complex cases, the free water deficit can be calculated and advice can be sought from Biochemistry physicians to guide the rate of water replacement.

Guideline reviewed: February 2026

Page updated: August 2026