Hyponatraemia

Disclaimer These guidelines have been produced to guide clinical decision making for the medical, nursing and allied health staff of Perth Children’s Hospital. They are not strict protocols, and they do not replace the judgement of a senior clinician. Clinical common-sense should be applied at all times. These clinical guidelines should never be relied on as a substitute for proper assessment with respect to the particular circumstances of each case and the needs of each patient. Clinicians should also consider the local skill level available and their local area policies before following any guideline.  Read the full PCH Emergency Department disclaimer.

Aim 

To guide PCH Emergency Department staff with the assessment and management of hyponatraemia.

Definition

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

Background¹

• 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 sodium 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.

General

• 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 Syndrome of Inappropriate Diuretic Hormone Secretion (SIADH).

Causes of Hyponatraemia

• Administration of hypotonic fluids
• SIADH 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

Assessment

• 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 clinician advice as urgent treatment is required.

History

• 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.

Examination

Symptoms of severe hyponatraemia include:

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

Investigations

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

Management

• If there are no neurological manifestations of hyponatraemia correction with hypertonic saline is unnecessary and potentially harmful.
• Avoid rapid correction of hyponatraemia. Corrections of >8mmol/L/24 hours can lead to brain damage (central pontine myelinolysis).⁶
• Symptomatic hyponatraemia is a medical emergency. Notify Paediatric Critical Care (PCC) urgently and arrange for senior medical review.

Management of symptomatic hyponatremia^2,3

• Sodium should be corrected to 125mmol/L or until seizures stop if this occurs first:
  • Give an intravenous infusion of 3mL/kg sodium chloride 3% over 20 minutes (maximum 150mL/dose). See Sodium Chloride 3% and 23.4% (Hypertonic Saline) Monograph - Medication Management Manual (internal WA Health only)
  • Sodium should then be re-measured
  • A further 3ml/kg sodium chloride 3% should be administered if seizure continues and Na <125mmol/L.
• Where possible sodium chloride 3% should be given via a central line as it is hypertonic. If a central line is not available do not delay administration; administer via a peripheral line. Monitor carefully for potential extravasation and local tissue damage.
• Aim is to correct the serum sodium by no more than 5-6mmol/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 8mmol/L per 24 hours.
• Measure serum sodium and electrolytes after initial corrections and repeat every 2 to 4 hours until stable.

Management of asymptomatic hyponatraemia

• Note: Active correction with sodium chloride 3% 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 serum sodium ≥130mmol/L:

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

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

• Administer IV sodium chloride 0.9% with glucose, if appropriate
• Measure serum sodium and electrolytes 4 hours after commencing/altering therapy and repeat every four hours until stable.

Nursing

• 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.
• Sodium chloride 0.9% + glucose 5% should be the intravenous fluid of choice in children at risk of developing hyponatraemia.
• Children with confirmed hyponatraemia should have their electrolytes measured every 4 hours until stable.
• Observations to include monitoring of blood pressure

References

1. Zieg J, Diagnosis and management of hyponatraemia in children. Acta Paediatrica 2014; 103, 1027-2034
2. Somers MJ & Traum AZ. Hyponatraemia in Children: Evaluation and Management [Internet]. Waltham MA: UpToDate; 2021 [cited 03/12/2021]. Available from: https://www-uptodate-com.pklibresources.health.wa.gov.au/contents/hyponatremia-in-children-evaluation-and-management?search=hyponatreamia%20children&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1#H3027125697
3. Sterns RH, Nigwekar SU, Hix JK. The treatment of hyponatremia. Semin Nephrol 2009; 29:282. 

Further reading

1. Bruce, Robert C. and Robert M. Kliegman. “Hyponatremic seizures secondary to oral water intoxication in infancy: association with commercial bottled drinking water.” Pediatrics 100.6 (1997): e4
2. Moritz, Michael L., and Juan Carlos Ayus. “New aspects in the pathogenesis, prevention, and treatment of hyponatremic encephalopathy in children.”Pediatric Nephrology 25.7 (2010): 1225-1238
3. Rodríguez, M. Jose, et al. “Neurological symptoms in hospitalised patients: do we assess hyponatraemia with sufficient care?.” Acta Paediatrica 103.1 (2014): e7-e10
4. Bhalla, P., et al. “Lesson of the week: hyponatraemic seizures and excessive intake of hypotonic fluids in young children.” BMJ: British Medical Journal319.7224 (1999): 1554
5. Brenkert, Timothy E., et al. “Intravenous hypertonic saline use in the pediatric emergency department.” Pediatric emergency care 29.1 (2013): 71-73
6. Farrell, Cristina, and Marcela Del Rio. “Hyponatremia.” Pediatrics in Review 28.11 (2007): 426-428

Endorsed by:	Drugs and Therapeutics Committee	Date:	Nov 2021
		Review date:	Nov 2024

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