Fluid and Electrolyte Balance and Nutrition
Fluid questions test maintenance calculation, dehydration assessment, and safe intravenous fluid selection; nutrition questions test feeding progression.
Core rules
- Holliday-Segar maintenance: 100 mL/kg/day for the first 10 kg, 50 for the next 10, 20 for each kilogram thereafter. Hourly equivalent is 4-2-1 mL/kg/hr.
- Dehydration: mild under 5%, moderate 5–10%, severe over 10% weight loss.
- Oral rehydration is first line for mild-to-moderate dehydration: small frequent volumes, about 5 mL every 1–2 minutes.
- Resuscitation uses 20 mL/kg isotonic boluses. Maintenance should be isotonic fluids with dextrose and potassium chloride; hypotonic fluids cause hospital-acquired hyponatremia.
- Do not add potassium until urine output is documented.
- Nutrition: breast milk or formula to 12 months, no cow's milk before 12 months, vitamin D 400 IU daily, iron-fortified solids introduced around 6 months, no honey under 12 months.
Worked example
Calculate maintenance for a 26 kg child. First 10 kg = 1000 mL, next 10 kg = 500 mL, remaining 6 kg × 20 = 120 mL. Total is 1620 mL/day, or about 68 mL/hr. If the child is also 8% dehydrated, replace the deficit (0.08 × 26 = 2.08 kg = 2080 mL) over roughly 24 hours in addition to maintenance and ongoing losses, with reassessment of electrolytes and urine output.
Traps
- Using hypotonic maintenance fluid, the leading cause of pediatric hyponatremia.
- Starting potassium before voiding.
- Giving a bolus of hypotonic fluid or dextrose-containing fluid for shock.
- Introducing cow's milk or honey before 12 months.