Clinical meaning
Pediatric fluid and electrolyte management differs fundamentally from adult management due to children's higher metabolic rate, greater body surface area-to-weight ratio, higher total body water percentage (75-80% in newborns vs 60% in adults), and immature renal concentrating ability. These factors make children more susceptible to fluid imbalances and more rapid progression to dehydration. Maintenance fluid requirements are calculated using the Holliday-Segar method: 100 mL/kg/day for the first 10 kg, 50 mL/kg/day for the next 10 kg, and 20 mL/kg/day for each kg above 20 kg. The equivalent hourly rate is the 4-2-1 rule: 4 mL/kg/hr for first 10 kg, 2 mL/kg/hr for next 10 kg, 1 mL/kg/hr for each kg above 20 kg. Dehydration is classified as mild (3-5% body weight loss in infants, 3% in adolescents), moderate (6-9% in infants), and severe (>=10% in infants). Isotonic dehydration (proportional loss of water and sodium) is most common (80% of cases). Hypotonic dehydration (greater sodium than water loss) leads to intracellular edema and is more hemodynamically dangerous. Hypertonic dehydration (greater water than sodium loss) causes intracellular dehydration and neurological symptoms and requires SLOW correction to prevent cerebral edema. Pediatric electrolyte ranges differ: potassium is normally slightly higher in neonates (3.5-6.0 mEq/L) and serum sodium normal range is the same as adults (135-145 mEq/L) but neonates are less able to concentrate urine.