Pediatric emergency medicine trisk 1892 1892
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“normal” urine output. With severe dehydration, the child may have signs of altered mental
status.
Triage
Recognize the dehydrated child and consider DI in the setting of dilute urine output with
hypovolemia. Children with known DI will decompensate if noncompliant with medication or
any illness.
Initial Assessment/H&P
A history may be elicited of the child’s awakening in the middle of the night to drink. In the
young infant who is not provided with adequate fluids and consequently is chronically
dehydrated, the child may fail to thrive or may have a history of intermittent low-grade fevers
due to intermittent hypernatremia. However, if the cries of the infant are interpreted as hunger
rather than thirst, the infant with DI may be obese.
Physical examination may be normal, or signs of dehydration, such as dryness of mucous
membranes, decreased skin turgor, sunken eyes, and in an infant, a depressed anterior fontanel,
may be present. Because of the hyperosmolarity, the degree of dehydration may be
underestimated on physical examination. Hypothalamic or pituitary lesions can lead to other
endocrine abnormalities such as secondary hypothyroidism and growth failure. A
craniopharyngioma or optic nerve glioma may affect the visual fields or cause raised
intracranial pressure, which is indicated by papilledema.
Management/Diagnostic Testing
DI is diagnosed by demonstrating that the kidneys fail to concentrate urine when fluid intake is
restricted. This condition can be difficult to prove in children. Criteria for the diagnosis of DI
may be met by finding an elevated serum osmolality (greater than 300 mOsm/L) and an
elevated serum [Na+ ] (greater than 145 mEq/L) in the presence of dilute urine (osmolality less
than 600 mOsm/L). Blood glucose and serum creatinine levels are normal.
In many cases, the diagnosis can be ruled out by the demonstration of appropriately
concentrated urine and normal serum osmolality on specimens obtained upon awakening. The
definitive diagnosis is made by a formal water deprivation test. This test is performed
electively in cases in which the diagnosis is uncertain and should never be performed if the
child is already dehydrated. The measurement of ADH by radioimmunoassay is available but
generally is not useful in the diagnosis of DI.
In most cases, a diagnosis of DI is not known at the time of presentation; therefore, the acute
management is directed toward correction of the dehydration and the hyperosmolar state. The
treatment of DI is similar to that described for hypernatremic dehydration (see Chapter 22
Dehydration ), with the notable addition that the fluid required for the replacement of urinary
fluid losses will be far greater. In fact, the high urinary output, despite significant dehydration,
often provides the first and most convincing evidence for DI.
If the child is hypotensive or if the serum [Na+ ] is greater than 160 mEq/L, initial volume
expansion is necessary, using 20 mL/kg normal saline during the first hour or more rapidly, if
needed. Once an adequate intravascular volume has been achieved, further fluid replacement is
