Pediatric Doses and Other Calculations
Safe dose ranges, body surface area, maintenance fluids and intake and output
Is the ordered dose safe? (4 steps)
- Weight in kg.
- Calculate the safe range from the reference (mg/kg/day or mg/kg/dose).
- Calculate what the order gives (per dose or per day: compare like with like).
- Inside the range → calculate the volume. Outside → hold the dose and call the prescriber.
Worked examples
| Problem | Working | Result |
|---|---|---|
| Amoxicillin 200 mg PO every 12 h. Child 22 lb. Safe: 25–45 mg/kg/day. Supply 400 mg/5 mL | 22 ÷ 2.2 = 10 kg → safe 250–450 mg/day. Order = 400 mg/day → safe. 200 ÷ 400 × 5 | 2.5 mL per dose |
| Acetaminophen 240 mg PO every 6 h. Child 18 kg. Max 15 mg/kg/dose. Supply 160 mg/5 mL | Max 270 mg/dose → safe. 240 ÷ 160 × 5 | 7.5 mL |
| Cefazolin 500 mg IV every 8 h. Child 12 kg. Safe: 25–100 mg/kg/day | Safe 300–1,200 mg/day. Order = 1,500 mg/day | Unsafe: hold and clarify |
Body surface area (Mosteller)
BSA (m²) = √(height cm × weight kg ÷ 3,600)
Example: 150 cm, 45 kg → √(6,750 ÷ 3,600) = √1.875 = 1.37 m². Used for chemotherapy and some pediatric doses.
Maintenance fluids (Holliday-Segar)
100 mL/kg/day (first 10 kg) + 50 mL/kg/day (next 10 kg) + 20 mL/kg/day (each kg above 20).
Example: 15 kg → 1,000 + 250 = 1,250 mL/day ≈ 52 mL/h.
Intake and output
- Intake: oral fluids, IV fluids and flushes, tube feeds and water flushes, irrigant not returned, and foods liquid at room temperature (gelatin, ice cream, popsicles, soup). Ice chips ≈ half their volume as water.
- Output: urine, emesis, diarrhea, drains, NG output, wound drainage.
Example: milk 240 mL + juice 120 mL + IV 100 mL/h × 8 h (800 mL) + ice chips 200 mL (= 100 mL) → intake 1,260 mL. Urine 650 + 400 mL + emesis 150 mL → output 1,200 mL.
Memory hook
"Per day ÷ doses per day = per dose." Many pediatric errors happen when a daily dose is given as each dose.