Hypernatraemia
On this page
Definition
Hypernatraemia is defined as a serum sodium concentration of >145 mmol/LHypernatraemia represents a deficit of water relative to sodium and is always associated with high serum osmolality.
Aetiology
Underlying aetiology is most commonly due to water loss (either due to inadequate water intake or excessive fluid losses) but on rare occasions hypernatraemia may result from sodium overload.Causes of hypernatraemia
- Dehydration
- Osmotic diuresis e.g. hyperosmolar non-ketotic diabetic coma
- Diabetes insipidus
- Excess IV saline
- Excessive fluid loss eg. burns, intestinal fistula, D&V, excessive sweating in high temperatures
- Excess salt intake
- Hyperaldosteronism
Signs & symptoms
- Lethargy
- Weakness
- Confusion
- Irritability
- Myoclonic jerks
- Seizures
- Signs of hypovolaemia (tachycardia, hypotension, poor skin turgor, dry mucosa etc)
Initial investigations
- Bloods including U&E's, glucose and calcium levels
- Lithium levels if patient takes lithium
- Urine and serum osmolality
Hypernatraemia reduces lithium elimination and increases the risk of toxicity
Hypernatraemia should be corrected with great caution. Although brain tissue can lose sodium and potassium rapidly, lowering of other osmolytes (and importantly water) occurs at a slower rate, predisposing to cerebral oedema, resulting in seizures, coma and death.
Although there are no clinical guidelines by NICE or Royal College of Physicians at present, it is generally accepted that a rate of no greater than 0.5 mmol/hour correction is appropriate.
Although there are no clinical guidelines by NICE or Royal College of Physicians at present, it is generally accepted that a rate of no greater than 0.5 mmol/hour correction is appropriate.