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Hyponatraemia


  • Statewide logo

    This guideline has been adapted for statewide use with the support of the Victorian Paediatric Clinical Network

  • See also

    Hypernatraemia
    Intravenous Fluids
    Diabetes Mellitus (including DKA)

    Key Points

    1. Prevention involves identifying children at risk (i.e. those with conditions associated with increased ADH secretion) and restricting their fluid to 1/2-2/3 maintenance of isotonic solution.
    2. A child’s fluid status is key in determining the cause of hyponatraemia and dictating treatment.
    3. The rate of correction of hyponatraemia should not exceed 8mmol/L in 24 hours as over rapid correction can cause osmotic demyelination syndrome.
    4. Hyponatraemic seizures and/or altered conscious state are a medical emergency and can cause irreversible neurological damage.

    Background

    Hyponatraemia is defined as serum sodium < 135mmol/L.

    • Most children with Na > 125mmol/L are asymptomatic.

    Hyponatraemia and rapid fluid shifts can result in cerebral oedema causing neurological symptoms.

    • If Na < 125mmol/L or if serum sodium has fallen rapidly vague symptoms such as nausea and malaise are more likely and may progress.
    • If Na < 120mmol/L: headache, lethargy, obtundation and seizures may occur.
    • Chronic hyponatraemia (developing > 24 hours) may have more subtle features such as restlessness, weakness, fatigue or irritability (due to cerebral adaptation)

    Rapid correction of hyponatraemia can result in osmotic demyelination syndrome which manifests as irreversible neurologic features (dysarthria, confusion, obtundation and coma) which often present days after sodium correction.   

    Causes (common causes in bold)

    Fluid Overloaded

    Euvolaemic

    Dehydrated

    • IV fluid administration in excess of the child’s needs
    • Nephrotic syndrome
    • Cirrhosis
    • Heart Failure
    • Acute/ Chronic Renal Failure
    • Obstructive uropathy

     
    • Administration of enteral hypotonic fluids (including dilute formula, Oral Rehydration Solutions, excessive water intake)
    • Psychogenic Polydipsia
    • Increased ADH secretion
      • Pulmonary: pneumonia, bronchiolitis,  mechanical ventilation
      • CNS: infections, injury, tumour
      • Post-operative, trauma, pain
      • Endocrine: Hypothyroid, low cortisol
    • Medications
      • Chemotherapy (cyclophosphamide, vincristine, platinum based agents)
      • Antiepileptics (valproate, carbamazepine, oxcarbazepine)
      • Vasopressin
    • GI losses and rehydration with free water
      • Gastroenteritis
      • Secretory/osmotic diarrhoeas
      • Ostomies
    • Skin losses (CF / burns)
    • Abdominal 3rd spacing
    • High rate fluid consumption post exercise
    • Hyperglycaemia 
    • Renal Losses
      • Thiazide Diuretic
      • Cerebral salt wasting
    • Primary renal Tubular Disorders
    • Hypoaldosteronism
    • Metabolic alkalosis

     

    Assessment

    • History consistent with common causes for hyponatraemia
    • History of fluid intake/losses
    • Clinical assessment of the child’s current hydration status
    • Neurological status
    • Red Flags
      • Nausea and vomiting
      • Irritability
      • Headache
      • Decreased conscious state
      • Seizures

    Management

    Investigations (recommended if Na < 130mmol/L)

      • Paired serum and urine osmolality
      • Urinary sodium
      • BSL (If hyperglycaemia present in addition to hyponatraemia see DKA)
      • Consider blood gas if sick

    Prevention

    Special attention should be paid when prescribing fluids to children with conditions associated with increased ADH secretion

    • Only give isotonic fluid (e.g.: 0.9% Saline + 5% glucose) as maintenance fluids.
    • Only give 1/2- 2/3 maintenance rate if child is euvolaemic
    • Measure UEC at baseline, then monitor daily while on fluids
    • Regular weights 

    Treatment 

    • Management is determined by presence of seizures/ altered conscious state and fluid status (see flow chart below).  
    • The target rate of serum sodium correction is 6-8mmol/L in 24 hours (unless seizing- see flow chart below).
    • All children should have a strict fluid balance including weight (minimum daily, but maybe 6-12 hourly for more unwell children).   
    • Remember to treat the underlying cause.


    diagram hyponatraemia
       

    *Notes

    • Risk of morbidity from delayed treatment is greater than the risk of osmotic demyelination from overly rapid correction. Therefore, aggressive initial correction is indicated for the first 3-4 hours (or until symptoms resolve) at a rate not to exceed 2 mmol/L per hour
    • Hyponatraemic seizures may be refractory to anticonvulsants and sodium correction should not be delayed
    • 3% Saline should preferably be given via a central line


    Consider consultation with local paediatric team when:

    • Sodium level < 130mmol/L or the child is symptomatic
    • Correction > 8mmol/ L in 24 hours
    • Children requiring care beyond the comfort of the local hospital

    Consider transfer when

    • Sodium < 125mmol/L
    • The child has had CNS symptoms including seizures or altered conscious state

    For emergency advice and paediatric or neonatal ICU transfers, call the Paediatric Infant Perinatal Emergency Retrieval (PIPER) Service: 1300 137 650. 

    Information specific to RCH

    Consider discussion with ICU and/or Endocrinology team if Na < 125mmol/L

    Last revised August 2018