Hyponatraemia is defined as serum sodium <135mmol/L. It
represents an excess of water in relation to sodium in
extracellular fluid. Symptoms are likely with Na <125
mmol/L or if the serum sodium has fallen rapidly.
The main causes of hyponatraemia in children
Less common but important causes are:
Special attention should be paid when administering intravenous
fluid to children with conditions associated with high ADH levels
and impaired free water excretion (see above). (see IV
Most children with mild to moderate hyponatraemia are
asymptomatic or manifest the symptoms of the underlying disease
(bronchiolitis, meningitis etc). The symptoms and signs of
severe hyponatraemia are predominately neurological:
Assess the patient's hydration state. (see
If Na+ <130 mmol/L: measure serum potassium, chloride, urea,
creatinine and glucose.
Measure the urinary sodium and osmolarity.
In the presence of hyperlipidaemia (e.g. nephrotic syndrome) or
hyperpoteinaemia, some laboratories produce falsely low
measurements of serum sodium (this is not the case at RCH).
This is sometimes called pseudohyponatraemia. Contact your
The ideal rate of serum sodium correction depends on the
presence and severity of symptoms. Correction that is too
rapid (>8 mmol/L Na+/24h) can result in cerebral demyelination,
especially of the pons, with risk of severe and lasting brain
injury. This is especially a risk if hyponatraemia has been
present for more than 5 days and is rapidly corrected.
Management of children without specific symptoms of
hyponatraemia depends on volume status. They may be normally
hydrated, moderately dehydrated or severely dehydrated (see
Active correction of hyponatraemia (e.g. with 3% NaCl) is not
necessary. Allow the plasma sodium concentration to rise at
no more than 8 mmol/L per day using the guidelines below, based on
hydration state. Continue correction to 135 mmol/L.
1. The child with normal or increased volume
2. The child with moderate dehydration and serum sodium
Try nasogastric rehydration. When using Gastrolyte,
remember that it contains 60mmol/L of sodium; rapid re-hydration
may make the Na+ fall faster than is safe.
If NG rehydration is not possible or results in a too rapid fall
in sodium give iv 0.9% NaCl (see severe dehydration below).
3. The child with severe dehydration or serum sodium
Give iv 0.9% NaCl (plus 5% glucose) until the child can take
Measure electrolytes every 4 hours until stable, whether on iv
or nasogastric rehydration.
Hyponatraemia occurs because high plasma glucose increases serum
osmolarity, causing a shift of water from the intracellular space
into extracellular fluid. The reduction in blood glucose
after beginning treatment may correct the hyponatraemia, through a
shift of water back to the intracellular space. However if
the serum sodium fails to increase as the glucose falls
hyponatraemia should be actively corrected. This will prevent
a reduction in serum osmolality, which carries an increased risk of
cerebral oedema. Using 0.9% NaCl solution as the fluid for
DKA resuscitation will generally maintain the osmolarity. (see DKA
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