[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Conditions](https://durgical.com/en/conditions/) › Hypernatraemia [Conditions](https://durgical.com/en/conditions/) · [Metabolism (biochemistry)](https://durgical.com/en/conditions/) # Hypernatraemia Blood sodium is high because water is lacking; it happens in people who cannot drink or lose a lot of water, and neurons shrink. Updated 2026-11-01 ## Structures involved Tap one to see what it is and open it in 3D. - [Hypothalamus](https://durgical.com/en/anatomy/hypothalamus/) - [Kidneys](https://durgical.com/en/anatomy/kidney/) - [Pituitary gland](https://durgical.com/en/anatomy/pituitary-gland/) - [White matter](https://durgical.com/en/anatomy/white-matter-of-telencephalon/) ## In biochemistry - [Serum osmolality and osmolar gap](https://durgical.com/en/biochemistry/topics/serum-osmolality-and-osmolar-gap/) ## In physiology - [Body fluid compartments](https://durgical.com/en/physiology/body-fluid-compartments/) - [Osmosis, osmolarity and tonicity](https://durgical.com/en/physiology/osmosis-osmolarity-and-tonicity/) - [Cell volume regulation](https://durgical.com/en/physiology/cell-volume-regulation/) - [The posterior pituitary: ADH and oxytocin](https://durgical.com/en/physiology/the-posterior-pituitary-adh-and-oxytocin/) - [Heat exhaustion and heat stroke](https://durgical.com/en/physiology/heat-exhaustion-and-heat-stroke/) - [The countercurrent mechanism, urea recycling and urine concentration](https://durgical.com/en/physiology/the-countercurrent-mechanism-urea-recycling-and-urine-concentration/) - [ADH, thirst and water balance](https://durgical.com/en/physiology/adh-thirst-and-water-balance/) - [Reasoning through fluid and electrolyte imbalances](https://durgical.com/en/physiology/reasoning-through-fluid-and-electrolyte-imbalances/) - [Fluid shifts between compartments](https://durgical.com/en/physiology/fluid-shifts-between-compartments/) - [Urine dilution, free water and osmotic diuresis](https://durgical.com/en/physiology/urine-dilution-free-water-and-osmotic-diuresis/) ## What it is A high serum sodium that nearly always reflects a deficit of free water relative to sodium, with hyperosmolality. ## Who gets it It mainly affects dependent older adults, infants with diarrhoea and intensive care patients; thirst protects anyone with free access to water. ## Causes - Water loss without replacement: fever, sweating, burns, osmotic diarrhoea, vomiting - Central diabetes insipidus (no ADH: head trauma, pituitary surgery, tumours) or nephrogenic (lithium, hypercalcaemia, hypokalaemia) - Osmotic diuresis: hyperglycaemia, mannitol, urea from high-protein feeds - No access to water or impaired thirst: dementia, infants, intubated patients - Sodium gain: hypertonic solutions or bicarbonate, errors in mixing infant formula ## Risk factors - Older age or dementia - Infants with diarrhoea - Critically ill or tube-fed patients - Lithium treatment - Surgery or trauma near the pituitary ## Pathophysiology When free water is lacking, plasma osmolality rises; water leaves cells by osmosis and neurons shrink, stretching and tearing bridging veins (haemorrhage) and disturbing their function: irritability, lethargy, seizures and coma. Normally hyperosmolality triggers thirst and ADH release from the posterior pituitary; if thirst, water access or ADH action fails, sodium rises. Over days neurons generate osmolytes to regain volume, so overly fast correction produces brain oedema. ## Classification - Hypovolaemic: loss of water and some sodium (diarrhoea, sweat) - Euvolaemic: pure water loss (diabetes insipidus, fever) - Hypervolaemic: sodium gain (hypertonic solutions) - Acute ( - Intense thirst (if preserved) - Irritability and high-pitched cry in infants - Lethargy, confusion - Weakness and muscle twitching - Seizures and coma when severe - Polyuria with dilute urine in diabetes insipidus ## Red flags - Falling consciousness or seizures - Dehydrated infant with extreme irritability - Fast correction of chronic hypernatraemia (risk of brain oedema) ## Diagnosis **Clinical** Assess hydration, access to water, urine output and drugs. **Tests** Serum sodium and osmolality, urine osmolality and sodium, glucose, calcium, potassium, creatinine; water deprivation test and response to desmopressin to tell central from nephrogenic diabetes insipidus. **Imaging** MRI of the sella and [hypothalamus](https://durgical.com/en/anatomy/hypothalamus/) if central diabetes insipidus is confirmed; head CT if neurological status worsens. ## Treatment **Medical** Replace the free water deficit (oral, by tube or with intravenous hypotonic fluids) gradually **Medical** Central diabetes insipidus: desmopressin; nephrogenic: treat the cause (stop lithium, correct calcium and potassium) and thiazides or a low-solute diet **Medical** Hypovolaemia or shock: isotonic fluid first to restore perfusion **Follow-up** Frequent sodium checks so it is not lowered faster than is safe in chronic forms ## Complications - Brain haemorrhage from shrinkage - Venous sinus thrombosis - Brain oedema from fast correction - Rhabdomyolysis ## Prognosis Hypernatraemia in older adults and critically ill patients is linked to high mortality, partly from the underlying illness. ## Prevention - Offering water to dependent people - Mixing infant formula correctly - Monitoring sodium and urine output on lithium or after pituitary surgery ## Test yourself Think of the answer, then tap the question to see it. ## What does hypernatraemia nearly always reflect? A deficit of free water relative to sodium, not an excess of body sodium. ## Which mechanism protects a healthy person from hypernatraemia? Thirst, triggered by hyperosmolality, together with ADH release. ## How is central diabetes insipidus told from nephrogenic? After water deprivation, urine concentrates with desmopressin in the central form and not in the nephrogenic form. ## Why is chronic hypernatraemia corrected slowly? Neurons have generated osmolytes; lowering sodium fast draws water in and causes brain oedema. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/conditions/hypernatraemia/) ## Related conditions - [Hyponatraemia](https://durgical.com/en/conditions/hyponatraemia/) - [Hypercalcaemia](https://durgical.com/en/conditions/hypercalcaemia/) - [Hypokalaemia](https://durgical.com/en/conditions/hypokalaemia/) - [Acute (viral) gastroenteritis](https://durgical.com/en/conditions/acute-gastroenteritis/) - [Traumatic brain injury](https://durgical.com/en/conditions/traumatic-brain-injury/) Educational information, not medical advice. For any symptom, see a health professional. Sources: [Sodium Blood Test: MedlinePlus Medical Test](https://medlineplus.gov/lab-tests/sodium-blood-test/) (MedlinePlus, US National Library of Medicine, 2026); [Sodium blood test: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/003481.htm) (MedlinePlus, US National Library of Medicine, 2026); [Dehydration: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000982.htm) (MedlinePlus, US National Library of Medicine, 2026); [Diabetes insipidus: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000377.htm) (MedlinePlus, US National Library of Medicine, 2026); [Nephrogenic diabetes insipidus: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000511.htm) (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011). 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