Gastrointestinal Disorders, Nutrition, and Fluid/Electrolyte Management
Maintenance and deficit fluids
Holliday-Segar: 100 mL/kg/day for the first 10 kg, 50 for the next 10, and 20 for each kilogram above 20 - equivalently the 4-2-1 rule in mL/kg/hour. Use isotonic fluid (lactated Ringer or normal saline with dextrose and potassium) for maintenance; hypotonic fluids cause hospital-acquired hyponatremia. Resuscitation is 20 mL/kg isotonic boluses. Mild-to-moderate dehydration responds well to oral rehydration solution, 50 mL/kg over 4 hours for mild and 100 mL/kg over 4 hours for moderate dehydration.
Correction rates
Correct hyponatremia no faster than 8–10 mEq/L in 24 hours to avoid osmotic demyelination; correct chronic hypernatremia no faster than 10–12 mEq/L per day (about 0.5 mEq/L/hour) to avoid cerebral edema. Neonatal hypoglycemia: 2 mL/kg of D10W bolus followed by a continuous infusion.
GI pharmacotherapy
Infant GERD is managed with conservative measures; proton pump inhibitors are not recommended under 1 year for uncomplicated reflux. Constipation: polyethylene glycol 3350 at 0.4–0.8 g/kg/day. Ondansetron 0.15 mg/kg (max 8 mg) for acute gastroenteritis-related vomiting. Inflammatory bowel disease uses mesalamine, immunomodulators, and infliximab with therapeutic drug monitoring.
Nutrition
Term infants need roughly 100–120 kcal/kg/day; preterm infants 120–150 kcal/kg/day with 3–4 g/kg/day protein. Refeeding syndrome (hypophosphatemia, hypokalemia, hypomagnesemia) follows rapid refeeding of a malnourished child - start low and advance slowly with electrolyte monitoring.
Worked example
Maintenance for a 25 kg child: (4 × 10) + (2 × 10) + (1 × 5) = 65 mL/hour, or 1560 mL/day. Any ongoing losses are replaced separately.