Hypernatremia is defined as serum sodium of more than 150 mEq/L.
Hypernatremia in newborns is usually because of dehydration:
- Inadequate breastfeeding causes hypernatremic dehydration
- Decreased breastfeeding frequency causes an increase in breast milk sodium levels – this can also cause hypernatremia
- Faulty radiant warmer causing hyperthermia
- Hypernatremia in extremely preterm baby can be due to excessive transepidermal water loss – avoid this condition by frequently monitoring serum electrolytes and appropriate adjustments in fluid administration
- Osmotic diuresis because of hyperglycemia
Hypervolemic hypernatremia in newborns can be because of:
- Improperly mixed formula
- Sodium bicarbonate administration
- Excess saline administration
- Primary hyperaldosteronism
Hypernatremia causes increased osmolarity in the extracellular compartment – intracellular water shifts to the extracellular compartment.
This is why newborns with hypernatremic dehydration do not show overt clinical signs of dehydration until late in the course of the disease.
In response to hypernatremia-induced hypertonicity in the extracellular compartment, brain cells produce osmoles using amino acids and organic solutes. Osmoles increase osmotic pressure inside the neurons which counter the egress of free water from neurons.
If hypernatremia is corrected rapidly, there is a rapid fall in extracellular osmolarity. Rapid fall in extracellular tonicity causes movement of water in brain cells causing brain edema and morbid neurological complications.
This is why hypernatremia should be corrected slowly, at a maximum rate of 0.5 mEq/L/hour or 12 mEq/L/day.
Treatment of Hypernatremic Dehydration
Step 1: Estimate the Degree of Dehydration
Calculation of dehydration by pre-dehydration weight
If you know the baby’s accurate weight before the onset of dehydration, subtract the current weight to estimate the degree of dehydration.
Clinical estimation of dehydration
Use the clinical estimate if you don’t have pre-dehydration weight.
Lethargy, weakness, irritability, coma, altered mental status, seizures, severe oliguria, thrombosis, brain hemorrhage, tachypnea, respiratory failure, and doughy skin texture are the signs of severe dehydration (≥ 15%).
Treat hypernatremic dehydration in two phases: Emergency phase to rapidly restore intravascular volume, and Rehydration phase to slowly correct remaining free water and solute fluid deficit over next hours to days.
Step 2: Emergency Phase
Give 10-20 mL/kg isotonic fluid bolus IV over 20-30 minutes.
Normal Saline (Sodium 154 mEq/L) is not isotonic in hypernatremic dehydration.
So, if we give normal saline bolus to a patient having serum sodium 190 mEq/L, we will give 19% free water. This free water will rapidly decrease serum sodium levels causing brain edema.
Increase sodium concentration of bolus fluid up to 10-15 mEq/L lower than serum sodium levels by adding 3% saline (513 mEq/L) to bolus fluid when serum sodium is more than 175 mEq/L.
Amount of 3% saline (mL) to be added to 1 L NS to increase its sodium concentration can be calculated with this formula:
Step 3: Rehydration Phase
Correct free water deficit, solute fluid deficit and give maintenance fluid in the rehydration phase.
Replacing Free water deficit – This will normalize serum sodium
Restore normal serum sodium at a rate of no more than 0.5 mEq/L/h or 12 mEq/L/d.
Faster correction rates cause brain edema in hypernatremic dehydration – correct slowly over 48 hours or more.
Calculate free water deficit by this formula:
Decide the correction fluid according to serum sodium levels:
145 – 165: D5 0.2NS
165 – 185: D5 0.45NS
>185: Normal Saline
Solute fluid deficit – Electrolyte containing fluid of the deficit
Despite hypernatremia, these patients also have a deficit of sodium.
Solute fluid is electrolyte-containing fluid lost from the body.
Give half of the total solute fluid in the first 8 hours and the remaining half over the next 16 hours.
Withhold potassium from solute fluid until good urine output is established.
Give D5 0.2NS which contains 31 mEq/L of sodium according to the baby’s requirement.
Withhold potassium from maintenance fluid until good urine output is established.
Monitoring during Rehydration
- Monitor serum electrolytes 2-4 hourly for the first 24 hours or until the rate of sodium correction stabilizes.
- If sodium decline is > 0.5 mEq/L/h, decrease the rate of IV fluid infusion or increase sodium in IV fluid.
- Further monitor serum sodium every 4-6 hourly until normal.
- Monitor urine output. Add 20 mEq/L potassium in maintenance fluid once good urine output is established.
- Monitor blood glucose. Hypernatremia is associated with hyperglycemia.
- [edited by] Christine Gleason, Sandra Juul. Avery’s Diseases of the Newborn, 10th Edition. Elsevier, 2017
- [edited by] Lauren Kahl, Helen Hughes. The Harriet Lane Handbook, 21st Edition. Elsevier, 2017