Pediatric emergency medicine trisk 1893 1893
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accomplished slowly because overly rapid volume correction can cause cerebral edema,
seizures, and death.
If the child is not hypotensive, or once the hypotension and perfusion have been corrected,
free water replacement is done over 48 hours. Calculations of appropriate fluids must include
maintenance requirements, replacement needs, and ongoing urinary losses (see Chapter 22
Dehydration ).
If DI is strongly suspected on the basis of discrepant serum and urine osmolality,
Desmopressin (DDAVP®) (10 μg intranasally or 0.2 to 0.4 mCg/kg subcutaneously) may be a
useful adjunct to IV fluid therapy. If desmopressin is not available or cannot be used for some
reason, other antidiuretic agents are available. Aqueous vasopressin (Pitressin® ) may be
administered as a continuous IV infusion starting at 2.5 mU/kg/hr and slowly (every 15 to 30
minutes) increasing the rate by increments of 2.5 milliunits (maximum 10 mU/kg/hr) to
decrease urine output to less than 2 mL/kg/hr.
Desmopressin and vasopressin act rapidly to promote tubular resorption of free H2 O;
clinically, this response should be apparent as decreased urinary output, when being measured
with a bladder catheter, and should demonstrate increased urine osmolality within 15 minutes
of administration. Once the patient has responded, however, extreme care must be used in
subsequent fluid management because the patient can no longer excrete excess water.
Therefore, baseline IV fluid administration must be restricted to 1 L/m2 of body surface area
per day (or roughly two-thirds maintenance fluids) using a low sodium infusate, such as 5%
dextrose with one-fourth normal saline (0.23%), in addition to the fluid designed to replete the
initial estimated free water deficit over 48 hours.
Failure to respond to either form of ADH suggests the possibility of tubular
unresponsiveness to ADH (nephrogenic DI); however, more commonly, failure to respond
results from improper administration of the medication or use of desmopressin that has lost its
potency. Because of these factors, if cessation of diuresis is not noted within 2 hours of
administration of the first dose, a second dose from a different bottle of desmopressin should
be tried. The use of an ADH agonist generally simplifies management by reducing the quantity
of fluid that must be infused; however, careful monitoring of input and output remains
essential. Children who fail to respond to desmopressin are likely to have nephrogenic DI and
must be managed acutely with fluid therapy alone. Hypercalcemia and renal failure are the
most common causes of nephrogenic DI. Paradoxically, the thiazide diuretics have proven to
be useful in the chronic control of nephrogenic DI.
The child should be closely observed for changes in level of consciousness, pulse rate, and
blood pressure. Fluid input and output should be meticulously monitored. Serum osmolality
and [Na+ ] should be determined every 1 to 2 hours until the rate of their decline can be
determined. Urine osmolality should be measured every 1 to 2 hours to determine the
responsiveness of the renal tubule to DDAVP. Because large volumes of dextrose-containing
fluids are used, the blood glucose should also be followed closely. If the blood glucose exceeds
150 mg/dL, the concentration of dextrose in the infusate should be decreased.
Clinical Indications for Discharge or Admission
Clinically significant electrolyte derangements or the inability to maintain hydration status are
indications for admission in well-appearing child. Children with intact thirst mechanism who
