Paediatric Acute care Guidelines PMH Emergency Department

Hyponatraemia is defined as serum sodium (Na) <135mmol/L. It results from an excess of water relative to sodium in the extracellular fluid compartment. Symptoms are likely if Na <125mmol/L or if there has been a rapid fall in the sodium level.



  • Hyponatraemia is one of the most common electrolyte disorders encountered in children occurring in approximately 3% of hospitalised children
  • Under normal circumstances the human body can maintain Na within the normal range of 135-145 mmol/L
  • Hyponatraemia usually occurs in the setting of excess water intake with or without sodium losses, in the presence of impaired free water excretion
  • Administration of hypotonic fluids via the intravenous or enteral route is the most common cause of hospital acquired hyponatraemia


  • Usually the body can prevent hyponatraemia by generating dilute urine in order to excrete free water
  • Water excretion is often impaired secondary to increased anti-diuretic hormone (ADH) levels. If this occurs in the absence of osmotic or hypovolaemic stimulus it is termed SIADH. (Syndrome of Inappropriate Diuretic Hormone Secretion).

Causes of Hyponatraemia

  • Administration of hypotonic fluids
  • SIADH- Which can be caused by a number of medical conditions including:
    • Meningitis / Encephalitis
    • Pneumonia / Bronchiolitis
    • Surgery
    • Pain
    • Nausea / Vomiting
  • Water intoxication in infants receiving dilute formula or supplemental water
  • Medications
    • Diuretics
    • Desmopressin with associated relative excess fluid intake
  • Rarer causes include:
    • Adrenal insufficiency (congenital adrenal hyperplasia, Addison’s disease)
    • Defects in renal tubular absorption



  • Most children with mild to moderate hyponatraemia will be asymptomatic or have symptoms of their underlying condition
  • Rapid changes in sodium levels may cause headache, nausea, vomiting and weakness
  • Hydration status and intravascular volume status must be assessed as this will help establish the cause and influence treatment
  • If there is evidence of hyponatraemic encephalopathy (seizures, impaired level of consciousness) seek senior advice as urgent treatment is required


  • A detailed history of fluid intake, fluid losses and current medication must be taken
  • In admitted patients intravenous/enteral fluid administration, weight and fluid balance should be reviewed


Symptoms of severe hyponatraemia include

  • Headache
  • Nausea
  • Vomiting
  • Weakness
  • Impaired level of consciousness
  • Seizures
  • Encephalopathy
  • Respiratory Depression



  • Investigations should include measurement of plasma osmolality, urinary osmolality and urinary sodium
  • Urine osmolarity and plasma urea can differentiate the cause of the hyponatreamia
    • Osmolarity > 20mmol/L for dehydration, but < 20mmol/L for water intoxication
  • Paired plasma and urinary osmolality are needed to diagnose SIADH
  • Urinary sodium should also be checked, low urinary sodium suggests intravascular volume depletion



  • If there are no neurological manifestations of hyponatraemia correction with hypertonic saline is unnecessary and potentially harmful
  • Symptomatic hyponatraemia is a medical emergency. Notify ICU urgently and arrange for senior medical review.

Initial management

Management of Symptomatic Hyponatraemia

  • Sodium should be corrected to 125 mmol/L or until seizures stop if this occurs first:
    • Give an infusion of 3ml/kg 3% Saline over 30 minutes
    • Sodium should then be re-measured
    • A further 3ml/kg 3% Saline should be administered if still fitting and Na <125 mmol/L
  • Where possible 3% Saline should be given via a central line as it is hypertonic. If a central line is not available do not delay administration; careful use of a peripheral line is appropriate.
  • Aim is to correct the serum sodium by no more than 5-6 mmol/L over the first 2 hours
  • Fluid restriction alone has no role in the management of symptomatic hyponatraemia
  • When symptoms have resolved, aim to correct the hyponatraemia and dehydration over 48 hours. The sodium correction should not exceed 8 mmol/L per 24 hours.
  • Measure serum sodium and electrolytes after initial corrections and repeat every 4 hours until stable


Management of Asymptomatic Hyponatraemia

  • NOTE:  Active correction with 3% Saline is not necessary and potentially harmful
  • Management will depend on volume status:

If normal or increased volume status:

  • Fluid restrict to 60% of maintenance fluid
  • Do not give hypotonic fluids
  • Review medications history and treat any stimuli to ADH secretion

If mild-moderate dehydration and Na ≥130 mmol/L:

  • Consider enteral rehydration with oral rehydration solution
  • Close monitoring of electrolytes, ongoing losses and fluid losses
  • Remember oral rehydration solution is hypotonic and may result in a further fall in Na or failure to correct.  If this occurs give 0.9% Saline with 5% glucose if appropriate intravenously.

If severe dehydration or serum sodium <130 mmol/L:

  • Administer 0.9% Saline with 5% glucose if appropriate
  • Measure serum sodium and electrolytes 4 hours after commencing/altering therapy and repeat every 4 hours until stable



  • Any hospitalised child is at risk of hyponatraemia whether receiving enteral or intravenous fluids
  • Children with hyponatraemia should be monitored closely for altered neurological status and any concerns should prompt a medical review
  • Accurate daily weight, fluid intake, fluid output and balance should be recorded in all patients with hyponatraemia
  • 0.9% Saline + 5% Glucose should be the intravenous fluid of choice in children at risk of developing hyponatraemia (see ED Guideline:  Fluids – Intravenous Therapy).
  • Children with confirmed hyponatraemia should have their electrolytes measured every 4 hours until stable



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