Dehydration (pediatrics): Clinical sciences

Dehydration is a condition characterized by an excessive loss of body water. In children, dehydration most often results from acute gastrointestinal illnesses that cause vomiting, diarrhea, and decreased fluid intake. Less commonly, it can result from conditions associated with non-gastrointestinal fluid losses, such as polyuria, third spacing, or burns. Treatment of dehydration depends on its severity, which can be estimated from clinical findings.

Now, if a pediatric patient presents with a chief concern suggesting dehydration, first perform an ABCDE assessment to determine if they’re unstable or stable. If unstable, stabilize their airway, breathing, and circulation. Next, obtain IV or intraosseous access, and administer a bolus of an isotonic crystalloid, such as normal saline. Finally, place your patient on continuous vital sign monitoring, and if needed, provide supplemental oxygen. Then, obtain a focused history and physical examination, and order a BMP and urine studies including urine osmolarity, specific gravity, and sodium.

History usually reveals vomiting or diarrhea, which is often accompanied by decreased fluid intake. They also could have increased insensible losses from fever, excessive sweating, or sometimes extensive burns. Less commonly, your patient may have an underlying condition causing polyuria, such as diabetes mellitus or diabetes insipidus.

Patients with severe dehydration are generally unstable and present with signs of shock. Pulses are typically weak, and perfusion is poor. These patients usually have skin tenting and very dry mucous membranes, with severely reduced or absent urine output. In children, late findings include drowsiness or lethargy, and vital signs will reveal tachycardia and hypotension in more severe cases.

As for labs, the BMP may reveal hypo- or hypernatremia. You might also see hypokalemia, especially in patients with profuse diarrhea; or hyperkalemia, in the setting of acute kidney injury. A decreased bicarbonate level indicates metabolic acidosis, which is often caused by diarrhea; whereas an increased bicarbonate level indicates metabolic alkalosis, which often results from excessive vomiting. The blood urea nitrogen level and serum creatinine are also typically elevated. Finally, urine studies will reveal increased urine osmolarity, increased urine specific gravity, and decreased urine sodium.

These clinical findings indicate severe dehydration, which means your patient has a volume loss of 10 percent or more. Patients with severe dehydration are critically ill and require immediate resuscitation to restore intravascular volume and improve perfusion. If you haven’t already done so, administer a 20 milliliter per kilogram bolus of normal saline, and repeat boluses until your patient no longer demonstrates signs of shock. Then, replace the remaining fluid deficit.

Now, to calculate your patient's total deficit, multiply the estimated percentage of dehydration by their weight in kilograms. Each kilogram represents one liter of fluid. For example, a 10-kilogram child with a 10 percent deficit has lost one kilogram, which equals one liter of fluid. Next, subtract the volume of fluid boluses that you’ve already given from the total deficit, to determine the remaining fluid deficit.

Replace this remaining deficit over 24 hours. While you do so, you’ll also need to provide isotonic maintenance fluids for insensible losses and replace ongoing losses from diarrhea or vomiting with a suitable replacement solution. Maintenance fluids should contain appropriate concentrations of glucose and potassium. Before adding potassium to maintenance fluids, make sure your patient is voiding and that their serum potassium is not elevated.

Here’s your first clinical pearl! Children with diarrhea and hypotonic fluid intake can lose excessive amounts of sodium and water, which triggers ADH secretion, and consequently leads to hyponatremia. If sodium levels fall rapidly, these patients can develop signs and symptoms of hyponatremic encephalopathy, such as vomiting and seizures.

Treat hyponatremic encephalopathy with hypertonic saline but remember to correct sodium levels slowly to decrease the risk of osmotic demyelination syndrome; and avoid hypotonic solutions as they can worsen hyponatremia.