Hypernatraemia in children

High Serum Sodium is worrying if Na >150mmol/L; and considered severe if >170mmol/L

 

Causes

Net loss of water

 – Inadequate breastfeeding or other feeding difficulties

 – GI losses: Vomiting, NGT drainage, diarrhoea; laxatives

 – Renal loss: Loop, osmotic diuretics, polyuria in Acute Tubular Necrosis

 – Skin losses: Burns, Insensible water losses

 – Diabetes insipidus

 

Excess sodium intake

 – Inappropriate IV fluids, or Sodium bicarbonate

 – Concentrated formula feeds

 – Ingestion or poisoning with salt

 – Endocrine: Hyperaldosteronism, Cushing syndrome

 

Clinical presentation

Shock occurs late even with dehydration because intravascular volume is relatively preserved.

 

Clinical assessment may underestimate true degree of dehydration, as skin feels ‘doughy’; but child may appear sicker.

 

Severe symptoms mainly develop with acute hypernatraemia & slow increase in Na over few days can be well tolerated because of cerebral compensation.

 

Slight increase in serum Na increases thirst, with neurological features of irritability or lethargy, tremors or ataxia. Severe hypernatremia leads to seizures and reduced consciousness.

 

Investigation

 – Check serum and urine- paired electrolytes and osmolality

 – Investigations for finding cause

 – Check blood glucose

 

Management

 – Treat hypotension or shock with boluses of 0.9% saline; repeat if necessary

 

 – Fluid management should then be based on the initial serum sodium

 – Give maintenance & total deficit fluid (slowly replaced over 48 hours) with 0.9% NaCl

 

 – If seizures / reduced GCS- Consider neuroimaging; then

 – Monitor U&E and Intake-Output at least every 8 to 12 hourly

 – Replace any ongoing gut losses and ml-for-ml with normal saline

 

Remember to stop any source of excess Sodium & do not allow a thirsty child with severe hypernatremia to drink excess fluids orally

 

Rapid reduction of S Na can cause cerebral oedema, convulsions and permanent brain injury. Aim to lower the serum Na slowly at 0.5mmol/L/hour (max 12mmo/L in 24h)

 

If the serum sodium falls rapidly slow the rate of rehydration and seek senior advice, including Renal team or PICU

 

Severe hypernatraemic dehydration Na⁺≥ 170 may require PICU management