Hypernatremia In Children

Hypernatremia

Nelson defines it as a serum sodium concentration of more than 145mEq/L. Nelson also accepts that in certain institutions or countries, serum sodium ≥150mEq/L is taken to be hypernatremia. Normal Serum Na⁺  Concentration is 135- 145 mEq/L

Common Causes In Children

1. Excess sodium intake/sodium intoxication
   • Usually, when there is increased sodium intake, there is also a thirst mechanism that comes into play and the patient tries to consume more water. In case there is increased sodium intake which cannot be compensated by water or the person is unable to consume water. The person will develop hypernatremia. Improperly mixed or prepared infant formulas.
   • Excess sodium bicarbonate ingestion can happen in 2 scenarios:
     • Iatrogenic: Large amounts (>1-2mEq/Kg) amounts of sodium bicarbonate are given to the patient. If higher doses are given, sodium load can produce hypernatremia in the patient and these patients will have severe metabolic alkalosis associated.
     • Abuse of sodium bicarbonate-containing antacids: Many of the antacids and baking soda-like preparations contain large amounts of sodium bicarbonate. Due to acid reflux or acidity, or ayurvedic preparations, if these are consumed in large amounts, they can develop hypernatremia.
   • Seawater/salt solution ingestion: if a child has somehow consumed seawater or taken seawater for any purpose, it can result in hypernatremia. Use of IV hypertonic saline: 3% saline is useful in many indications including rest ICP but it can produce hypernatremia. Hyperaldosteronism: aldosterone produces sodium retention and potassium excretion. Therefore, large amounts of aldosterone use can always lead to hypernatremia. Salt poisoning: there may be child abuse or Munchhausen syndrome by proxy which can lead to hypernatremia.
2. Water deficit 
   • If the patient is not consuming water at all, then there will be a relative increase in the Na concentration in the body.  Dehydration will be produced and cause a water deficit. Dehydration will have some degree of sodium loss.
   • Pure water deficit is seen in certain conditions and the most common of which are:

1. Diabetes Insipidus (DI)

• Central DI: There will be less or an absence of secretion of vasopressin from the hypothalamic-pituitary axis. Central DI can be of 2 forms: 1) Genetic and 2) acquired. There is also another form called Wolfram syndrome
• Nephrogenic DI: this can also be of 2 forms: 1) Genetic and 2) acquired.

2. Increased insensible losses

• There will be complete water loss from the body and the Na intake will be insufficient to compensate for that. It can happen in premature infants. It can happen in radiant warmers. It can happen with phototherapy given for neonatal jaundice,

3. Reduced water intake

• In poor breastfeeding. Adipsia – the absence of thirst which can happen in hypothalamic injury or hypothalamic lesion. Child neglect or child abuse can also lead to hypernatremia.

C. Water and sodium deficit

• Loss of water is more severe than loss of sodium. The Na concentration tends to increase and lead to hypernatremia. A typical example of this is

1. GIT losses

• An example of GIT loss is diarrhea. The fluid that is passed out is hypotonic. If the hypotonic fluid is not replenished with fluids, the patient can end up having hypernatremic dehydration. Vomiting or nasogastric suction. Lactulose abuse – also called Cathartics abuse.

2. Cutaneous losses

• Burns, Excess sweating

3. Renal losses

• Mannitol or other osmotic diuretics. Diabetes mellitus – hyperglycemia can act as a diuretic agent. Chronic kidney disease, post obstructive diuresis. The polyuric phase of ATN.

Scenario Of Diarrhoea: How Hypernatremic Dehydration Occurs

• Whenever there is viral diarrhea or simply a diarrhoeal illness in a child, the fluid which is getting lost is hypotonic. Nelson says that it has a Na concentration somewhere around 35-45mEq/L. water loss is more than Na loss because it is a hypotonic fluid. So, there will be 2 scenarios:
  • In case the child can take oral fluids, which are hypotonic, it can compensate for this loss and produce hyponatremic dehydration.
  • If the child is unable to drink, there will be more loss of water and more plain water is not coming into the child and this will produce hypernatremic dehydration.
• Essential hypernatremia: There is an injury to the hypothalamic posterior pituitary axis. It is a rare form in children. The patient is euvolemic and non-hypertensive. This may be associated with hypodipsia because there is a resetting of the osmolar sensors in the hypothalamus. 

Clinical Features Of Hypernatremia

The children may show the usual signs and symptoms of dehydration.

• If the symptoms are present, they are usually mild and tend to appear late. Hypernatremic dehydration is very problematic because, by the time child comes to medical attention, already severe intracellular dehydration has happened.

Pathophysiology

• If the serum Na concentration increases in the blood (outside the cell), the amount will also increase in the intracellular fluid. Sodium is more outside compared to inside but there is a delicate balance. If this balance is disturbed and hypernatremia happens (more sodium outside the cell), there will be a net movement of water outside the cell into the ECF. This will lead to: Cellular dehydration. The blood volume will be restored so there will be no hypotension despite dehydration happening in the patient. So, they will come to attention late. The intracellular fluid volume is restored so the usual signs and symptoms of dehydration such as skin pinch test will be normal. The patient is having dehydration, and the cells are losing water but the signs of dehydration will be minimal or absent which is not good because the cells are dying due to the absence of water.
• Nelson says that if the skin of these patients is checked, the skin pinch test may be normal but there will be a doughy feel of the skin, especially in the abdominal region.

1. CNS features

• The CNS features initially are non-specific: They include irritability, weakness, lethargy, and restlessness. Infants will have a high-pitched cry or hyperpnea. Nausea, increased thirst, and fever is often present which may or may not be related to the pathology. Hypernatremia can be associated with 2 problems: Hyperglycemia and hypocalcemia (mild in nature).
• Severe Hypernatremia: CNS hemorrhage will happen whenever there is a rise in the serum sodium level. Water from inside the neuron will move outside into the blood and CSF. So, two things will happen:
  • The amount of blood and CSF will suddenly increase and at the same time, neurons will shrink and move away from the skull attached to the inside. 
  • This sudden change will produce a scenario where there will be stretching and tearing of meninges and CNS blood vessels leading to the development of either subdural hemorrhage or subarachnoid haemorrhage or intraparenchymal haemorrhage.
• Nelson says that even though Central Pontine Myelinolysis is classically associated with overly rapid correction of hyponatremia, both central and Extra Pontine Myelinolysis can occur in children with hypernatremia.

2. Thrombotic complications

• It is seen in severe hypernatremia associated with dehydration. It includes Strokes, Dural sinus thrombosis, Peripheral             thrombosis, Renal vein thrombosis.

Clues To Underlying Diagnosis

• How to confirm if the patient is having hypernatremia due to salt poisoning or hypernatremic dehydration? Nelson says that the easiest way is to look for FeNa⁺ (fractional excretion of sodium). In the case of salt poisoning, the FeNa⁺ used is usually more than 1% whereas, in hypernatremic dehydration, the FeNa⁺ is on the lower side. If hypernatremia is associated with hypertension, hypokalemia, and severe alkalosis, the patient should be evaluated for hyperaldosteronism.
• In case of suspected Diabetes Insipidus (DI)- Check for urine and serum osmolality. Check for ADH levels in the blood and perform a water deprivation test.  This will help in confirming the diagnosis and knowing whether it is a nephrogenic type or a central type of DI.
• For renal vs. extra renal losses, the two can be easily distinguished by doing a urine analysis. Whenever there is a renal loss (more water is getting lost compared to sodium), the fractional excretion of sodium is >1% whereas in extra renal losses there will be concentrated urine with fractional excretion of Na <1%.

Also Read: Electrolyte Disturbances : The Basics">Fluid and Electrolyte Disturbances : The Basics

IDIOGENIC OSMOLES – A DOUBLE-EDGED SWORD

• Idiogenic osmoles are special osmotic molecules or complexes that are generated inside the neurons in chronic/slowly developing hypernatremia. The aim is to increase cellular osmolality and prevent the movement of water from the neurons to the outside.
• When hypernatremia is corrected rapidly, this moves water inside the neuron which can lead to the development of cerebral edema and can precipitate seizures in the patient.

Management

• If there is acute, severe hypernatremia, usually secondary to sodium administration can be corrected more rapidly with 5% dextrose in water (D5W) because Idiogenic osmoles have not had time to accumulate. If there is acute severe hypernatremia with volume overload, fluid cannot be given. So, a trial of loop diuretics like furosemide will be given intravenously. If furosemide is not effective, these patients usually need to be managed by dialysis. In the case of chronic hypernatremia, it is usually corrected very slowly. The target is the correction of <10mEq/L in 24 hours and the overall therapy should be taking around 2-4 days.
• No aggressive therapy needs to be given for hyperglycaemia or hypocalcaemia according to Nelson. Treat the underlying cause of hypernatremia.

Treatment Of Hypernatremic Dehydration

• Restoring intravascular volume
  • Normal saline is given as a relatively slow bolus – 20ml/kg is given over 20 min. No more than 2 boluses should be given.
• Correction of serum sodium
  • Determine the time for correction based on initial sodium concentration.
    • If the serum sodium is between 145-157mEq/L – correct the sodium level within 24 hrs.
    • If the serum sodium is 158-170mEq/L – correct the sodium level over 48 hrs.
    • If the serum sodium is 171-183mEq/L – correct the sodium level over 72 hrs.
    • If the serum sodium is 184-196mEq/L – correct the sodium level over 84 hrs.
• The commonly used fluid which is available in all the wards is N/2 in 5% dextrose. Some of the books including Indian textbooks say that it is N/3 or N/4 in 5% dextrose, but they are not easily available. 20mEq/L KCL should be added unless there is a contraindication for potassium at it. The requirement will be 1.25-1.5 times the maintenance. The slow correction needs to be done. When doing correction, the ongoing losses will be replaced.
• Monitor serum sodium every 4 hours. When correcting the serum sodium, it should not fall by >0.5mEq/L/h (the upper limit). If the serum sodium decreases too rapidly, either reduce the fluid rate or increase the sodium concentration in the fluid. This will ensure that the rate becomes controlled then being too rapid. If the serum sodium decreases too slowly, either increase the fluid rate or decrease the sodium concentration in the fluid making it even more hypotonic.
• If there are any features of decreased intravascular volume. During the correction, if it is found developing, another normal saline bolus of 20ml/kg can be considered. If seizures happen, rapid correction should be done. Rapidly restore the serum sodium level to safe levels and 3% hypertonic saline @ 4-6ml/kg IV over 30 min should be given.
• Sometimes, in textbooks, GIT and Cutaneous losses are also categorized together as extra renal losses to differentiate them from renal losses which have a slightly different mechanism. Nelson gives that if the skin of the patient is checked, the skin pinch test may be normal but there will be a doughy feel of the skin, especially in the abdominal region. The reason why hyperglycaemia and hypocalcaemia happen in hypernatremia is not clear. Severe hypernatremia can lead to CNS haemorrhage which can be life-threatening.

Also Read: Infections of the Upper Airway- Common Cold and Sinusitis

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