Hypernatraemia

• sodium >145 mmol/l

• almost always due to water loss

• major defence against it is thirst

Clinical Features

• nausea

• vomiting

• fever

• confusion

• convulsions if severe

Causes

• with deficient water intake

Water Losses

• insensible

  • sweating (increased in fever, high temperatures, exercise)

  • burns

  • respiratory infection

• renal loss

  • central diabetes insipidus

  • nephrogenic diabetes insipidus

  • osmotic diuresis

• GI loss

  • osmotic diarrhoea

  • malabsorption

  • infectious enteritis

• Hypothalamic disorders

  • primary polydipsia

• Water loss into cells

  • severe exercise

  • seizures

  • rhabdomyolysis

• Metabolic

  • Cushing's

Excess exogenous sodium

• hypertonic saline

• sodium bicarbonate used in resuscitation

• dietary sodium especially in infants where renal excretion poor

Investigating

• If minimal contraction of extracellular fluid

  • diabetes insipidus - confirm lack of ADH by Water Deprivation Test

• If expansion of ECF then sodium overload present

  • exogenous

  • excess adrenocortical hormone, e.g. Cushing's syndrome

• If contraction of ECF then losing water faster than sodium

  • urine loss - polyuria

  • sweating

  • GI losses

Treatment

• 0.9% saline initially if severe (>170mmol/l)
  • aim to correct over 48 hours to avoid cerebral oedema
• 5% dextrose
  • dangerous

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