Hypernatraemia

Exam Cram

• Hypernatraemia is a biochemical sign defined a serum sodium above 145mmol

• Hypernatraemia is defined as high sodium concentration, therefore it is caused by lack of fluid (hypovolaemia) or high Na+ (sodium retention)

• Work up: serum osmolality paired with urinary sodium & osmolality

• Management: treat underlying cause, IVF: glucose 5%

Outline

Diagnosis

Diagnostic criteria: serum Na+ > 145

Classification: severity

• Mild: 140-170

• Severe: > 170

Management

Basic

• Treat underlying cause

• Work up: blood glucose, calcium, urea & electrolytes

Severity

• Mild: Na 140-170: 

  • PO or IVF: Dextrose 5%

  • Daily Na+

• Severe: Na+ > 170

  • 8hrly Na+ 

  • Euvolaemia: dextrose 5%

  • Hypovolaemia: NaCl 0.9%

Complications

Central Pontine demyelination: when Na+ corrected > 10mmol in 24hrs, causes irreversible damage to central pons

Med Reg Notes

End of Life Care

My experience in internal medicine is that an acute hypernatraemia can be a sign of organ/ body dysfunction and that we may be entering an end of life phase and there is evidence to suggest hypernatraemia is a poor prognostic sign. 

Resources and References

1. Maggs FG. The management of patients presenting with hypernatraemia: is aggressive management appropriate? Clin Med (Lond). 2014 Jun;14(3):260-3. doi: 10.7861/clinmedicine.14-3-260. PMID: 24889569; PMCID: PMC4952537. 

2. https://handbook.ggcmedicines.org.uk/guidelines/electrolyte-disturbances/management-of-hypernatraemia/

Written in 2025