See also

Hypernatraemia
Intravenous Fluids

Diabetes Mellitus

Diabetic Ketoacidosis

Electrolyte abnormalities

Key points

1. Prevention involves identifying children at risk (ie 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 8 mmol/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 <135 mmol/L.

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

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

• If Na <125 mmol/L or if serum sodium has fallen rapidly vague symptoms such as nausea and malaise are more likely and may progress.
• If Na <120 mmol/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 <130 mmol/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 (eg: 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.

   

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

Consider transfer when

• Sodium <125 mmol/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 <125 mmol/L

Last revised August 2018