See also

Electrolyte abnormalities
Intravenous Fluids
Diabetic Ketoacidosis
Hypernatraemia

Key points

1. Fluid status is key in determining the cause of hyponatraemia and dictating treatment 
2. The rate of correction of hyponatraemia should not exceed 8 mmol/L in 24 hours in a non-seizing child
3. Hyponatraemic seizures are a medical emergency and may be refractory to anticonvulsants; do not delay sodium correction

Background

• In children, the normal range of sodium is 135-145 mmol/L
• Hyponatraemia usually occurs due to excess water intake or impaired free water excretion
• Acute hyponatraemia can result in cerebral oedema
• Severity:
• Mild (125-135 mmol/L): most children are asymptomatic
• Moderate (120-125 mmol/L): children may have non-specific symptoms such as nausea and malaise
• Severe (<120 mmol/L): headache, obtundation and seizures may occur
• Chronic hyponatraemia (developing >48 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
• Isotonic fluids are those containing a similar sodium concentration to plasma (sodium ≥125 to 160 mmol/L) eg 0.9% sodium chloride, Plasma-Lyte 148 and Hartmann’s solution
• Hypotonic fluids contain a sodium concentration less than that of plasma (sodium <125 mmol/L) eg Oral Rehydration Solution

Causes

 Assessment

• Focus assessment on the cause of hyponatraemia (consider child’s fluid status, duration of hyponatraemia and severity of symptoms)
• The speed of onset of hyponatraemia is often a better predictor of risk of neurological compromise than the sodium level
• Exclude pseudo-hyponatraemia secondary to, for example high blood glucose (see Diabetes Mellitus, Diabetic Ketoacidosis), mannitol or sorbitol

History

• Fluid intake and losses
• Underlying cause, for example: infections, malignancy, trauma
• Medications which may cause SIADH
• Neurological status
• Red Flags
• Nausea and vomiting
• Irritability
• Headache
• Decreased conscious state
• Seizures

 Examination

• Fluid status
• Weight
• Signs of cerebral oedema
• Evidence of underlying infective or malignant cause

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)
• Corrected sodium in hyperglycaemia = serum Na + (BSL-5)/3
• Consider blood gas if significantly unwell

Treatment 

• Management is determined by presence of seizures/altered conscious state and fluid status
• The target rate of serum sodium correction is 6-8 mmol/L in 24 hours (unless seizing, see flowchart below)
• All children should have a strict fluid balance including weight
• Treat the underlying cause

Management approach

Consider consultation with local paediatric team when

• Sodium level <130 mmol/L or the child is symptomatic
• Correction >8 mmol/L in 24 hours
• Child has complex fluid requirements (eg parenteral nutrition)

Consider transfer when

• Sodium <125 mmol/L
• CNS symptoms including seizures or altered conscious state
• Requiring care beyond the comfort level of the hospital

For emergency advice and paediatric or neonatal ICU transfers, see Retrieval Services

Consider discharge when

Cause for hyponatraemia identified and treated adequately

                                                                                                                                                                                 Last updated November 2023