Part of “CHAPTER 83 – ADRENOCORTICAL DISORDERS IN INFANCY AND CHILDHOOD“

Alo-ng with the well-known perturbations of fluid, electrolyte, and glucose homeostasis, adrenocortical diseases that occur in children also cause disturbed growth. The proper management of children with these disorders requires careful documentation of height and weight at regular intervals.

Physicians who are relatively unfamiliar with pediatric patients may assume that the fluid and electrolyte requirements of infants and children are similar to those of adults. Actually, infants are hypermetabolic, as compared to adults, because of the relatively large size of their high-energy-consuming organs (i.e., the brain, heart, liver, and kidneys) as compared to their somatic size. Water requirements change in proportion to caloric requirements. One milliliter of water is required for each kilocalorie of energy expenditure. Water and calorie requirements are approximately constant throughout life relative to surface area (1500 kcal/m² per day). Surface area can be calculated as the square root of (cm × kg/3600).

Normal daily sodium and potassium maintenance requirements are ˜2 mEq/dL and 1 mEq/dL water, respectively. When calculating electrolyte replacement, it must be remembered that the exchangeable fluid compartment is relatively larger in children than in adults, ranging from 60% of body weight in small children to 40% in adults. Because of the rapid rate of turnover of children’s body fluids, the electrolyte concentrations of parenteral fluids should be distributed evenly throughout the day to prevent shifts in the tonicity of body fluids.

Infants and children are intolerant of prolonged fasting because of their high metabolic rate and functionally immature gluconeogenic enzyme systems. When fasted, the normal young child will become hypoglycemic within as few as 20 hours. To prevent glycogenolysis, infants and young children need 6 to 8 mg/kg per minute of glucose.1