Hypernatraemia

Last updated:

Overview

Hypernatraemia is defined as a raised sodium concentration and hence serum osmolality. The sodium concentration is usually kept from rising by the effects of antidiuretic hormone (ADH, also known as vasopressin) which reduces the amount of water lost in the urine, stimulates thirst, and increases water intake. Increased loss of water can lead to hypernatraemia which can in turn cause dehydration as water moves from cells out into the extracellular fluid.

Epidemiology

  • More common in patients under intensive care where IV fluids are often given

Risk Factors

Causes

Hypovolaemic patients

  • Inadequate water intake
  • Diabetes insipidus
  • Impaired thirst mechanism (e.g. dementia/hypothalamic lesions)
  • Osmotic diuresis (e.g. mannitol use or hyperosmolar hyperglycaemic state)
  • Severe diarrhoea

Euvolaemic patients

  • Diabetes insipidus

Hypervolaemic patients

  • Iatrogenic:
    • Hypertonic saline
    • IV sodium bicarbonate water
  • Hyperaldosteronism
  • Excess salt consumption
    • Salt poisoning may be seen in children

Presentation

  • Features of water moving out of brain cells, leading to shrinkage:
  • Features of risk factors:
    • Dementia – can impair the thirst mechanism
    • Severe vomiting/diarrhoea
    • Polyuria, polydipsia, and nocturia – suggest diabetes insipidus
  • Features of hypovolaemia:

Management

  • 1st-line: treat underlying cause + treat dehydration + correct hypovolaemia (if present)
  • Hypernatraemia should be corrected with caution; correcting it too quickly can lead to cerebral oedema as the body adapts to the hypernatraemia
  • Correction should not be faster than 0.5 mmol/L/hour

Monitoring

  • Patients should be monitored and have their electrolytes checked regularly throughout and the rate of fluid given should be altered as necessary

Complications

  • Intracranial haemorrhage
  • Seizures
  • Coma
  • Cerebral oedema if correction is too quick

Author