Approach to hyponatremia (pediatrics): Clinical sciences

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Introduction0:00–0:36

Hyponatremia is a common electrolyte disturbance in which the serum sodium concentration is less than 135 milliequivalents per liter.
Several mechanisms can contribute to hyponatremia, including increased serum levels of antidiuretic hormone, or ADH; increased renal sensitivity to ADH; excessive free water intake; and low solute intake.
Now, based on the underlying cause, hyponatremia can be categorized as hypovolemic, euvolemic, and hypervolemic.Okay, if a pediatric patient presents with a chief concern suggestive of hyponatremia, you should first perform an ABCDE assessment to determine if they are unstable or stable.

Unstable patient0:36–1:39

If unstable, stabilize the airway, breathing, and circulation; obtain IV access and consider giving your patient IV fluids.
Next, put your patient on continuous vital sign monitoring, including blood pressure, heart rate, and pulse oximetry, and don’t forget to monitor your patient’s urine output!
Finally, if needed, provide supplemental oxygen.Now, here’s a high-yield fact to keep in mind! Unstable individuals with hyponatremia often have a sodium level below 125 milliequivalents per liter, which can result in cerebral edema and severe clinical manifestations, like seizures or even respiratory arrest!
If these findings are present, emergent administration of hypertonic saline might be necessary. Now, let’s go back to the ABCDE assessment and look at stable patients.

Stable Patient1:39–2:12

In this case, obtain a focused history and physical examination and order a basic metabolic panel, or BMP. Your patient may report symptoms like headache, nausea, vomiting, or confusion.
Lab results will reveal a sodium level lower than 135 milliequivalents per liter. With these findings, consider hyponatremia and order a plasma osmolality to help you determine the underlying cause.Let’s take a look when the plasma osmolality is above 295 milliosmoles per kilogram.

Hyperglycemia2:12–3:16

In this case, the plasma is considered hypertonic and indicates the presence of other osmotically active solutes, most commonly glucose.
In this case, consider hyperglycemia, so review the blood glucose from the BMP. If glucose is elevated, diagnose hyperosmolality due to hyperglycemia.
Here’s a clinical pearl to keep in mind! Plasma hypertonicity, or hyperosmolality, causes an osmotic shift of water from the intracellular space to the extracellular fluid, resulting in dilutional hyponatremia.
When you see an elevated plasma osmolality in the setting of hyponatremia, always make sure to check the serum glucose concentration!
For every 100 milligram per deciliter increase in serum glucose, serum sodium falls by about 1.6 milliequivalents per liter.On the other hand, if the plasma osmolality is between 280 and 295 milliosmoles per kilogram, consider pseudohyponatremia.

Pseudohyponatremia3:16–3:53

Next, order serum triglycerides and serum protein. If either of these are elevated, diagnose pseudohyponatremia, which is a lab artifact caused by high serum levels of triglycerides or protein, both of which can displace free water in the plasma, causing inaccurate measurement of sodium levels despite normal serum osmolality.On the other hand, if the plasma osmolality is below 280 milliosmoles per kilogram, the plasma is hypotonic, and you can confirm the diagnosis of hyponatremia.

Hyponatremia3:53–4:16

Next, assess the patient’s volume status.First, let’s discuss hypovolemic individuals. Physical exam findings often include an elevated heart rate and an orthostatic drop in blood pressure.

Hypovolemic Hyponatremia4:16–4:49

You may also notice sunken eyes, dry mucous membranes, and decreased skin turgor. These findings are highly suggestive of hypovolemic hyponatremia, so your next step is to order a urine sodium level to help you determine the underlying cause.If urine sodium level is less than or equal to 20 millimoles or milliequivalents per liter, consider extrarenal causes of sodium loss.

Extrarenal causes4:49–5:57

First, if your patient has a recent history of vomiting, diarrhea, or nasogastric suction, the underlying cause of hyponatremia is probably gastrointestinal loss of sodium.
On the other hand, if your patient has extensive burns or has been sweating excessively, they likely have insensible fluid losses.
Moreover, children with cystic fibrosis are susceptible to hyponatremia due to sodium loss through sweat. Finally, if your patient has a condition like pancreatitis, small bowel obstruction, or a severe allergic reaction, the most likely cause of your patient’s hyponatremia is third spacing.
Third spacing refers to the accumulation of extracellular fluid within extravascular spaces, such as the bowel lumen or peritoneum.

Renal causes5:57–7:55

Alright, now that we’ve discussed extrarenal causes of sodium loss, let’s go back and discuss patients whose urine sodium is greater than 20 millimoles per liter.
In these patients, you should consider renal causes of sodium loss.First, let’s discuss preterm or very-low-birthweight infants or VLBW.
In this case, hyponatremia is likely due to prematurity, since the kidneys of preterm infants are underdeveloped and have a limited ability to reabsorb sodium.
On the other hand, if your patient has recently taken thiazide, loop, or other diuretic, then your patient’s hyponatremia is likely the result of diuretic use.
Next, your patient might present with a known history of congenital adrenal hyperplasia, low blood pressure, and hyperkalemia.
In this case, the underlying cause of hyponatremia is likely mineralocorticoid deficiency related to the salt-wasting forms of congenital adrenal hyperplasia, such as 21-hydroxylase deficiency.
Now, if your patient has a history of renal tubular acidosis, or if labs demonstrate an elevated serum bicarbonate level, suggesting metabolic alkalosis, then your patient’s hyponatremia is likely the result of bicarbonaturia.
On the other hand, a condition affecting the central nervous system, like meningitis, head trauma, or recent brain surgery, in combination with an acute increase in urine output, is highly suggestive of cerebral salt wasting.
Finally, if your patient reports abdominal or flank pain with a diminished urinary stream, and the physical exam reveals a palpable distended urinary bladder, it’s likely that obstructive uropathy is the underlying cause of hyponatremia.Okay, let’s go back and consider euvolemic patients.

Euvolemic Hyponatremia7:55–10:26

The physical exam usually reveals a normal heart rate with no orthostatic drop in blood pressure. Mucous membranes will be moist, with normal skin turgor; and there are no signs of hypervolemia, such as ascites or subcutaneous edema.
This spectrum of findings is highly suggestive of euvolemic hyponatremia, which can be seen in hypothyroidism; glucocorticoid deficiency; syndrome of inappropriate ADH secretion; or water toxicity.
In these patients, your next step is to order urine sodium and random urine osmolality.First, let’s start with cases where urine sodium is less than or equal to than 20 millimoles per liter and random urine osmolality is less than or equal to 100 milliosmoles per kilogram.
This should make you consider the possibility of excessive free water intake. Some children may develop hyponatremia after unintentionally swallowing an excessive amount of water while swimming.
You may also have a child who is being fed diluted formula. Finally, iatrogenic water intoxication can occur when a child receives an excessive volume of hypotonic IV fluids.
These findings in your patient’s history are highly suggestive of water intoxication.Now let’s move on to cases where urine sodium is more than 20 millimoles per liter and random urine osmolality is greater than 100 milliosmoles per kilogram.
In this case you should order a TSH, and free T4; as well as a morning cortisol and an adrenocorticotropic hormone, or ACTH, stimulation test.
If the TSH is elevated and the free T4 is low, diagnose hypothyroidism. On the flip side, if the morning cortisol is low and the adrenocorticotropic hormone stimulation test demonstrates a decreased or absent cortisol response, diagnose glucocorticoid deficiency.
Lastly, if the TSH, free T4, and ACTH stimulation tests are all normal, diagnose syndrome of inappropriate antidiuretic hormone secretion, or SIADH for short.
Alright, let's go back one more time and discuss hypervolemic individuals. These patients might report an acute weight gain, which can be accompanied by orthopnea.

Hypervolemic hyponatremia10:26–12:14

The physical exam may demonstrate a dyspneic patient with evidence of increased jugular venous pressure. You may also notice subcutaneous edema or ascites.
These findings are highly suggestive of hypervolemia, and your next step should be to order a urine sodium level.First, let’s focus on patients that have urine sodium less than or equal to 20 millimoles per liter.
This suggests the presence of an edema-forming condition. If your patient has a known history of heart disease, with a physical exam revealing crackles and an S3 gallop on auscultation, heart failure is the likely cause.
On the other hand, a known history of liver disease, along with physical exam findings like ascites or spider angiomata, are highly suggestive of cirrhosis.
Finally, if your patient’s physical exam reveals peripheral edema, and labs reveal a normal BUN and creatinine, order a urinalysis.
If the urine protein is elevated, the underlying cause of hyponatremia is most likely nephrotic syndrome.Lastly, let’s look at patients with a urine sodium greater than 20 millimoles per liter.
If, in addition to that, your patient has an elevated serum BUN and creatinine, with a decreased glomerular filtration rate, the most likely cause of hyponatremia is renal failure.
In this case, think of acute kidney injury or chronic kidney disease.Alright, as a quick recap… If a patient presents with hyponatremia, order a plasma osmolality.

Review12:14–13:29

If it’s above 280 milliosmoles per kilogram, consider pseudohyponatremia or hyperosmolality; but if it’s below 280, diagnose hyponatremia and assess volume status.
For hypovolemic patients, if urine sodium is less than or equal to 20 millimoles per liter, consider extrarenal causes of sodium loss.
However, if urine sodium is above 20, consider renal causes of sodium loss. For euvolemic patients, if urine sodium is less than or equal to 20 and urine osmolality is less than or equal to100, consider excessive free water intake.
However, if urine sodium is above 20 and urine osmolality is above 100, investigate hormonal conditions. Finally, for hypervolemic patients, if urine sodium is less than or equal to 20, consider edema-forming conditions; and if it’s above 20 with a decreased GFR,