See also

Hyponatraemia
Intravenous fluids

Electrolyte abnormalities

Key points

1. Start treatment early with IV sodium chloride 0.9% + glucose 5%
2. The rate of correction should not exceed 0.5 mmol/L/hr, ie 10-12 mmol/L per day, to avoid cerebral oedema, seizures and permanent neurological injury
3. All children with moderate or severe hypernatraemia should have a paired serum and urine osmolality, but this should not delay treatment

Background

• Hypernatraemia is classified as:
  • Mild (146-149 mmol/L)
  • Moderate (150-169 mmol/L)
  • Severe (≥170 mmol/L)
• Moderate to severe hypernatraemia can cause acute brain shrinkage with vascular rupture, haemorrhage, demyelination and permanent neurological injury
• Infants and small children are more vulnerable to hypernatraemia due to greater insensible losses and inability to communicate their need for fluids or access fluids independently
• Chronic hypernatraemia (>48 hours) is often well tolerated and asymptomatic due to cerebral compensation

Causes:

Assessment

Red flags in red

History

• Fluid intake: detailed breast/formula/PEG feeding history – check feed concentration
• Fluid losses: GI, renal (polyuria), skin
• History of a midline brain defect
• History of renal disease
• Medications (consider diuretics, desmopressin, hypertonic fluids)

Examination

• Assess hydration status
  • Weigh bare child and compare with recent (within 2 weeks) weight recording
  • Serial weight measurements during treatment (up to every 6 hours depending on severity) are most helpful
  • Hypervolaemia with signs of oedema (eg periorbital, genital, sacral, peripheral) suggests sodium excess
  • Note: hydration assessment may be unreliable in chronic or severe hypernatraemia where clinical signs may underestimate degree of hypovolaemia
• Nonspecific initial signs:
  • Irritability, restlessness, weakness
• Followed by:
  • Vomiting, muscular twitching, fever, doughy skin
  • High pitched crying and tachypnoea in infants
• Severe signs (develop with acute rise of sodium >160 mmol/L)
  • Altered mental status
  • Lethargy
  • Seizures
  • Hyperreflexia
  • Coma

Investigations

Recommended if sodium ≥150 mmol/L

• UEC, calcium, magnesium, phosphate and glucose. These may need concurrent management
• In the presence of hypoalbuminaemia (albumin <30 g/L), a blood gas sodium level is more reliable
• Initial paired serum and urine sodium, creatinine and osmolality is ideal, but if results will be delayed, a urine dipstick for specific gravity will give an indication of urinary concentration and treatment should not be delayed

Evaluation of hypernatraemia using paired serum and urine osmolality:

Management

• Treat shock as a priority – see Resuscitation: Care of the seriously unwell child
• Once circulating volume is restored, the rate of sodium correction should be slow, no more than 0.5 mmol/L/hour
• Severe hypernatraemia (≥170 mmol/L) is a medical emergency and management is not discussed in this guideline. Refer to tertiary centre and contact ICU

Mild hypernatraemia (146-149 mmol/L)

• Manage the underlying cause and repeat UEC in 4-6 hours

Moderate hypernatraemia (150- 169 mmol/L)

General principles:

• Treatment is dependent on the underlying cause, water deficit (see table below) or sodium excess (see below)
• Restrict and record oral fluid intake as thirst can be excessive
• Cease any feed fortifications such as extra scoops of formula or polyjoule
• Monitor fluid status with urine output and repeated weights (weigh at least daily, and up to 6-hourly)
• Repeat UEC 1-2 hours after initial management then 4-6 hourly if the sodium level is decreasing at an appropriate rate
• If decrease in sodium is too rapid (>0.5 mmol/L/hr), cease or reduce the rate of fluids and seek expert advice early
• If hypernatraemia worsens or is unchanged, seek expert advice about hypotonic solutions
• Monitor neurological status closely

Treatment of moderate hypernatraemia due to water deficit

• Replace water deficit over 48 hours in addition to daily maintenance, with IV sodium chloride 0.9% and glucose 5% (see table for rates)  
• In addition, replace ongoing losses mL for mL (excluding urine) with IV sodium chloride 0.9%
• Once urine output is established, add potassium to the IV fluid prescription
• Treat diabetes insipidus with endocrinology input
• If seizures occur:
• consider venous sinus thrombosis or cerebral infarction
• consider imaging with a contrast CT scan
• contact ICU - may need hypertonic saline to slow a rapid decrease in sodium level

Fluid replacement table for hypernatraemic water deficit:

• The rates below include maintenance plus replacement of deficit over 48 hours, based on a presumption of 7% dehydration and moderate hypernatraemia
• These are starting rates only, and should be adjusted according to changes in sodium level on subsequent tests
• These rates do not include ongoing losses, which need to be added separately
• Severe hypernatraemia requires correction over several days, at a slower rate than this table describes

Treatment of moderate hypernatraemia due to sodium excess

• Aim to reduce excess sodium intake
• Get expert advice, as may need hypotonic fluid (eg sodium chloride 0.45%), or dialysis if overloaded
• Severe hypernatraemia (≥170 mmol/L) requires expert input

Consider consultation with local paediatric team when

Any child with moderate hypernatraemia (≥150 mmol/L)

Consider transfer when

• Hypernatraemia where the cause is unclear
• Hypernatraemia ≥170 mmol/L
• Displaying neurological symptoms
• Not responding to treatment as expected
• 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 hypernatraemia identified and treated adequately

Last updated October 2020