Holliday-Segar, 4-2-1, and isotonic maintenance

Maintenance (Holliday-Segar / NICE NG29): 100 mL/kg/day for first 10 kg + 50 mL/kg/day for next 10 kg + 20 mL/kg/day thereafter → 1000 + 500 + 40 = 1540 mL/day ≈ 64 mL/h. Hourly 4-2-1 rule: 4×10 + 2×10 + 1×2 = 40+20+2 = 62 mL/h. The common viva trap is writing 20 mL/kg × 12 kg = 240 mL for the last tier (that would be 1740 mL/day) — the last tier is only the kilograms above 20. Candidates should know both conventions and local charting.^[1][2]

Composition: isotonic crystalloid (sodium 131 to 154 mmol/L) with 5% glucose and potassium chloride once potassium is known — hypotonic 0.45% saline increases hospital-acquired hyponatraemia when non-osmotic ADH is high.^[2]

5% deficit: 50 mL/kg × 22 = 1100 mL. RCH: most children should have a maximum of 5% deficit replaced over the first 24 hours plus maintenance, then be reassessed. If the child is unwell, restrict maintenance to 50 to 80% (NICE NG29) or two-thirds (RCH).^[2]

DKA (if asked): NICE NG18 — 10 mL/kg of 0.9% saline over 30 minutes if dehydrated not shocked; immediately if shock (weak thready pulse and hypotension). Deficit 5% if pH is 7.1 or above, or 10% if pH is below 7.1, over 48 hours. Insulin 0.05 to 0.1 units/kg/h starting 1 to 2 hours after fluid.^[3]