Pediatric emergency medicine trisk 129

e-FIGURE 21.3 Blue dye causing localized cyanosis of the face and scalp of an infant. Note
the difference in color on the upper forehead which appears pink after wiping off the dye. This
dye originated from a blue blanket that the infant had been lying on. (Photo courtesy of David
Lowe.)


CHAPTER 22 ■ DEHYDRATION
SARAH D. MESKILL, ASHA T. V. MORROW

Dehydration is not a disease itself, rather a symptom of another process. Infants
have higher morbidity and mortality from dehydration and are more susceptible
to it because of their larger water content, three times higher metabolic turnover
rate of water than adults, renal immaturity, and inability to meet their own needs
independently. Children with various illnesses and circumstances will present to
the emergency department (ED) with signs of dehydration ( Table 22.1 ).
Gastroenteritis is the most common cause of dehydration in infants and children
and is the leading cause of death worldwide in children younger than 4 years of
age. In the United States, an average of 300 children younger than 5 years of age
die each year, and an additional 200,000 are hospitalized, secondary to diarrheal
illnesses with dehydration.

PATHOPHYSIOLOGY
In pediatrics, dehydration and hypovolemia are used interchangeably to describe
a reduction in the water content of the body. Over two-thirds of the total body
water is intracellular and one-third is in the extracellular space. Early in the
process of dehydration, the majority of the water loss is from the extracellular
compartment, which contains 135 mEq/L of sodium and negligible potassium.
However, with time, there is an equilibration between the extracellular
compartment and the intracellular compartment, which has 150 mEq/L of
potassium and negligible sodium. As the electrolyte composition of extracellular
fluid and intracellular fluid varies greatly, an understanding of this process helps

the clinician gauge the optimal composition and rate of fluid deficit correction
(see Chapter 100 Renal and Electrolyte Emergencies ).
Dehydration is often categorized by severity or degree of fluid deficit, severity
is judged by the amount of body fluid lost or the percentage of weight loss, and is
typically characterized as minimal (less than 3% of total body weight), mild to
moderate (3% to 10% of total body weight), or severe (greater than 10% of total
body weight). Most children have isotonic dehydration (with normal sodium
content) however both hyponatremic and hypernatremic dehydration can occur.


TABLE 22.1
CAUSES OF DEHYDRATION


Decreased intake
Physical restriction
Infant
Central nervous system depression
Anorexia
Voluntary or imposed cessation of drinking
Pharyngitis, stomatitis a
Respiratory distress a
Child abuse
Hypothalamic hypodipsia
Increased output
Insensible losses
Fever a
Sweating
Heat prostration
High ambient temperature/low humidity

Hyperventilation
Cystic fibrosis
Thyrotoxicosis
Renal losses
Osmotic
Diabetic ketoacidosis a
Acute tubular necrosis
High protein feeds
Mannitol usage
Nonosmotic
Diabetes insipidus
Sustained hypokalemia–hypercalcemia
Sickle cell disease
Chronic renal disease