Approach to hypernatremia (pediatrics): Clinical sciences

Hypernatremia is an electrolyte imbalance that occurs when the serum sodium concentration exceeds 145 milliequivalents per liter. It typically results from increased water loss or decreased water intake, but in rare cases, it can be caused by an excess salt load.

Now, based on the volume status, hypernatremia can be classified as hypovolemic, euvolemic, and hypervolemic hypernatremia! Okay, if a pediatric patient presents with chief concerns suggesting hypernatremia, you should first perform an ABCDE assessment to determine if they are unstable or stable.

If unstable, stabilize the airway, breathing, and circulation, obtain IV access, and consider IV fluids. Next, put your patient on continuous vital sign monitoring, including heart rate, blood pressure, and pulse oximetry; and don’t forget to monitor your patient’s urine output!

Now, here’s a clinical pearl! Patients with an acute rise in serum sodium concentration can develop neurologic complications, such as seizures and coma.

Moreover, increased serum osmolality causes water to rapidly shift out of cells, causing the brain to shrink, subsequently stretching intracranial blood vessels. In severe cases, blood vessels can rupture and result in intracranial hemorrhage.

Also, be cautious when treating hypernatremia, since aggressive correction of serum sodium levels or giving aggressive fluid resuscitation can lead to rapid fluctuations in serum osmolality, resulting in cerebral edema. Now, let’s go back to the ABCDE assessment and take a look at stable patients.

In this case, obtain a focused history and physical examination and order a basic metabolic panel, or BMP. Your patient or their caregiver will typically report neurologic symptoms, like irritability, restlessness, and sleepiness. Additionally, history often reveals a high-pitched cry in combination with increased thirst.

Meanwhile, the physical exam may demonstrate increased muscle tone and brisk reflexes; while the BMP will reveal serum sodium levels greater than 145 milliequivalents per liter. With these findings, you can diagnose hypernatremia, so your next step is to assess the patient’s volume status!

First, let’s focus on hypovolemic patients! In this case, the physical exam will reveal signs of dehydration, like elevated heart rate and an orthostatic drop in blood pressure. You may also notice sunken eyes, dry mucous membranes, decreased skin turgor, and a recent weight loss.

These findings are highly suggestive of hypovolemic hypernatremia, so your next step is to assess the patient’s urine output and urine osmolality.

If the urine output is reduced, meaning less than 1 milliliter per kilogram per hour, and urine osmolality is 750 milliosmoles per kilogram or greater, consider extrarenal fluid loss, such as insensible and gastrointestinal losses, or reduced fluid intake. Keep in mind that these are the most common causes of hypernatremia in children.

Now, first, let’s focus on hypernatremia due to insensible fluid losses! These patients might have extensive burns, or they might be sweating excessively. Additionally, they could have a fever or require the use of a radiant warmer, phototherapy, or mechanical ventilation. Any of these scenarios can be associated with insensible fluid losses, dehydration, and subsequent hypernatremia!

Next up are gastrointestinal fluid losses. These are usually associated with signs of gastrointestinal infections, like vomiting or diarrhea. Additionally, some patients might have an ongoing nasogastric suction, while others might be taking high doses of osmotic cathartics, such as lactulose.

No matter what the underlying cause is, your patient is losing excessive fluids over the gastrointestinal tract, which eventually results in dehydration, and again, hypernatremia!

Moreover, hypernatremia due to gastrointestinal loss represents the most common mechanism of hypernatremia in children and often occurs in combination with decreased free water replacement.

Finally, let’s go over inadequate fluid intake! Some common examples include infants with poor intake due to difficulty breastfeeding, children with an impaired thirst mechanism from neurologic conditions, like holoprosencephaly, as well as infants who are unable to communicate thirst to their caregiver! Any of these conditions can result in hypernatremia due to inadequate fluid intake.

Now, let’s go back and take a look at patients who are presenting with elevated urine output, meaning more than 4 milliliters per kilogram per hour, and urine osmolality below 750 milliosmoles per kilogram.

In this case, consider renal fluid losses as a cause of hypernatremia. For instance, a child might take diuretics for conditions like hypertension, congestive heart failure, or bronchopulmonary dysplasia. In these patients, hypernatremia is probably due to diuretic use!

On the other hand, your patient might present with a history of uncontrolled diabetes mellitus with hyperglycemia, or a recent intravenous mannitol administration. Glucose and mannitol are non-resorbable osmotic-active urinary solutes, and once filtered in the kidneys, they stimulate diuresis, eventually reducing the intravascular volume, which results in hypernatremia!

However, if your patient recently had surgical correction of an obstructive uropathy, such as posterior urethral valves or PUV, there’s a high chance that hypernatremia occurred due to post-obstructive diuresis.

Finally, if your patient has sickle cell disease, cystinosis, a recent acute kidney injury, or if they have acute tubular necrosis or ATN with polyuria, hypernatremia is probably caused by renal disease.

Okay, moving on to euvolemic patients. In this case, your patient or their caregiver may report polyuria, polydipsia, and secondary enuresis, which is loss of bladder control after a child has completed toilet training.

The physical exam typically reveals a normal heart rate without an orthostatic drop in blood pressure, as well as moist mucous membranes, normal skin turgor, and no weight loss. This spectrum of findings suggests euvolemic hypernatremia, so your next step is to order a urine and serum osmolality, and measure the patient’s urine output.