Pediatric Dehydration & Fluid Calculations (Pediatrics)

Prepared for Pass the Shift (owner: Kristina, RN). Always follow your facility’s protocols, provider orders, and current references.

1. Overview and Pathophysiology

Infants and young children are about 70–80% water (adults ~60%), have a higher metabolic rate, a larger surface area for their size, and immature kidneys that can’t concentrate urine well. They also depend on others for fluids. Together, that means they dehydrate faster. The most common cause is acute gastroenteritis (vomiting and diarrhea), plus poor intake, fever, and fast breathing.

Types by sodium: isotonic (most common; water and Na⁺ lost proportionally), hypotonic (Na⁺ < 130–135 — more Na⁺ lost; risk of cerebral edema/seizures), hypertonic (Na⁺ > 145–150 — more water lost; correct slowly to avoid cerebral edema; can look less ill than they are).

2. Signs by Severity

Finding	Mild (≈ 3–5%)	Moderate (≈ 6–9%)	Severe (≥ 10%)
Mental status	Alert	Irritable, restless, fatigued	Lethargic or unresponsive
Heart rate	Normal	Increased	Very high, weak pulse (bradycardia = very late)
BP	Normal	Normal (orthostatic changes)	Low (late)
Capillary refill	< 2 s	2–3 s	> 3 s, mottled, cool
Mucous membranes	Slightly dry	Dry	Parched
Tears	Present	Decreased	Absent
Fontanel (infant)	Flat	Sunken	Very sunken
Eyes	Normal	Sunken	Very sunken
Skin turgor	Normal	Slow recoil	Tenting
Urine output	Slightly decreased	< 1 mL/kg/h	Minimal/none

Weight is the best measure of fluid loss: % dehydration = (pre-illness weight − current weight) ÷ pre-illness weight × 100. 1 kg lost ≈ 1 L of fluid.

3. Diagnostics and Labs (ranges vary)

Daily weights (same scale, naked infant), strict I&O — weigh diapers (1 g = 1 mL)
Urine specific gravity (> ~1.020–1.030 suggests concentration)
Electrolytes and glucose for moderate–severe dehydration or IV therapy: Na⁺, K⁺ (don’t add K⁺ to IV fluids until the child is voiding and K⁺ is known), bicarbonate (low with diarrhea → metabolic acidosis), BUN/creatinine, glucose (hypoglycemia common in young children)

4. Treatment and Priority Nursing Care

Mild–moderate: is first-line

ORS (e.g., Pedialyte-type solutions) replaces water, sodium, potassium, and glucose. Avoid juice, soda, sports drinks, and plain water as the main fluid (wrong sugar/salt balance can worsen diarrhea or cause hyponatremia)
Common approach: 50–100 mL/kg over 3–4 hours (mild ~50, moderate ~100), plus replacement for ongoing losses (often ~10 mL/kg per diarrheal stool, ~2 mL/kg per emesis)
Small frequent amounts: 5 mL (1 tsp) every 1–2 minutes by syringe or spoon, increasing as tolerated — even vomiting children usually keep this down
Ondansetron (single dose) may be given to help a vomiting child tolerate ORS
Continue breastfeeding. Resume age-appropriate diet early once rehydrated (no need for BRAT-only diets or diluted formula)
NG rehydration if unable to drink

Severe dehydration or shock: IV

Isotonic crystalloid bolus 20 mL/kg (0.9% NaCl or lactated Ringer’s) over 5–20 minutes (or per order; 10 mL/kg for neonates or children with heart disease/concern for fluid overload)
Reassess after each bolus (HR, cap refill, mental status, BP, urine output, lung sounds, liver edge). Repeat as ordered
Then maintenance + deficit replacement; isotonic maintenance fluids with dextrose (e.g., 0.9% NaCl or balanced solution with 5% dextrose) are recommended for most hospitalized children (AAP 2018) to prevent hospital-acquired hyponatremia
Infusion pump always; check IV site hourly

5. Maintenance Fluid Calculation (Holliday-Segar)

Weight	24-hour rate (mL/day)	Hourly rate — 4-2-1 rule (mL/h)
First 10 kg	100 mL/kg/day	4 mL/kg/h
Next 10 kg (11–20)	+ 50 mL/kg/day	+ 2 mL/kg/h
Each kg above 20	+ 20 mL/kg/day	+ 1 mL/kg/h

Worked examples

8 kg infant: 8 × 100 = 800 mL/day (≈ 33 mL/h). 4-2-1: 8 × 4 = 32 mL/h
15 kg toddler: (10 × 100) + (5 × 50) = 1,000 + 250 = 1,250 mL/day (≈ 52 mL/h). 4-2-1: 40 + 10 = 50 mL/h
32 kg child: (10 × 100) + (10 × 50) + (12 × 20) = 1,000 + 500 + 240 = 1,740 mL/day (≈ 72.5 mL/h). 4-2-1: 40 + 20 + 12 = 72 mL/h

The 4-2-1 hourly rate and the daily rate ÷ 24 differ slightly — both are accepted approximations. Use the method your program teaches. Adult-sized teens are usually capped (often ~2,400 mL/day or 100 mL/h) per protocol.

Bolus: 20 mL/kg. Example: 18 kg child → 360 mL.

Urine output goals: infants/children ≥ 1 mL/kg/h (often 1–2); adolescents ≥ 0.5 mL/kg/h. Example: 12 kg toddler should make ≥ 12 mL/h.

6. Medications

Drug	Use	Notes
ORS	Rehydration	First-line for mild–moderate
Ondansetron	Vomiting interfering with ORS	Usually a single dose; QT prolongation caution
Isotonic crystalloids	Boluses and maintenance	Monitor Na⁺ and glucose
Zinc	Diarrhea in low-resource settings (WHO)	Shortens duration in deficient children
Avoid: antidiarrheals like loperamide in young children (risk of ileus); antibiotics only for specific bacterial causes

7. Complications and Emergencies

Hypovolemic shock: tachycardia, weak pulses, cap refill > 3 s, cool mottled skin, lethargy, then hypotension (late) → bolus and call for help
Hypoglycemia: check glucose in lethargic children
Hyponatremia/hypernatremia: seizures, altered mental status — correct sodium slowly per orders
Fluid overload from IV therapy: crackles, edema, hepatomegaly, rising weight, increased work of breathing — especially in infants and children with heart disease
Prerenal AKI

8. Education

Signs of dehydration to watch for: fewer wet diapers (e.g., none in 6–8 h for an infant), no tears, dry mouth, sunken eyes or soft spot, unusual sleepiness
How to give ORS in small sips; keep breastfeeding; resume normal foods
Hand hygiene and diaper-changing hygiene; rotavirus vaccine for infants
Return immediately for: lethargy, bloody stools, green (bilious) vomiting, persistent vomiting, signs of severe dehydration, infant < 3 months with fever

9. Memory Aids

4-2-1 per hour, 100-50-20 per day
Bolus = “20 for kids” (mL/kg), reassess after every one
“Pee 1 per kilo per hour” for kids
“Pee before K⁺” — no potassium in IV until voiding
“Small sips, big wins” — 5 mL every few minutes

10. NCLEX-Style Practice Questions

1. Calculate the 24-hour maintenance fluid requirement for a child who weighs 24 kg.

A. 1,580 mL
B. 1,580 mL/h
C. 2,400 mL
D. 1,200 mL

Answer: A. (10 × 100) + (10 × 50) + (4 × 20) = 1,000 + 500 + 80 = 1,580 mL/day (about 66 mL/h). C mistakenly uses 100 mL/kg for every kilogram.

2. A 14-kg toddler in hypovolemic shock is ordered an isotonic bolus of 20 mL/kg. How many mL should the nurse prepare?

A. 140 mL
B. 200 mL
C. 280 mL
D. 560 mL

Answer: C. 14 kg × 20 mL/kg = 280 mL. Reassess perfusion after the bolus.

3. A 2-year-old with mild dehydration from gastroenteritis vomits twice. Which instruction is best for the parent?

A. “Give only clear apple juice until the vomiting stops.”
B. “Give 5 mL of oral rehydration solution every few minutes and increase slowly.”
C. “Hold all fluids for 12 hours.”
D. “Offer full bottles of formula diluted with water.”

Answer: B. Small, frequent amounts of ORS are usually tolerated even with vomiting. Juice has too much sugar and too little sodium; holding fluids worsens dehydration; diluted formula is not recommended.

4. An IV order reads D5 0.9% NaCl with 20 mEq KCl/L for an infant who has not urinated in 8 hours. What should the nurse do first?

A. Start the infusion as ordered
B. Hold the potassium-containing fluid and verify renal function/voiding with the provider
C. Increase the rate to promote voiding
D. Give the fluid as an IV push

Answer: B. Potassium is added only after adequate urine output is confirmed, because poor kidney output can lead to dangerous hyperkalemia. Clarify the order and assess for voiding.

5. Which findings indicate severe dehydration in an infant? Select all that apply.

A. Capillary refill 4 seconds
B. Lethargy and difficult to arouse
C. Moist mucous membranes
D. Deeply sunken fontanel
E. Tears with crying

Answer: A, B, D. Delayed refill, lethargy, and a very sunken fontanel signal severe dehydration and possible shock. Moist membranes and tears indicate adequate hydration.

References

Daley, S. F., & Avva, U. (2024). Pediatric dehydration. In StatPearls. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK436022/

Feld, L. G., Neuspiel, D. R., Foster, B. A., Leu, M. G., Garber, M. D., Austin, K., Basu, R. K., Conway, E. E., Jr., Fehr, J. J., Hawkins, C., Kaplan, R. L., Rowe, E. V., Waseem, M., & Moritz, M. L. (2018). Clinical practice guideline: Maintenance intravenous fluids in children. Pediatrics, 142(6), e20183083. https://doi.org/10.1542/peds.2018-3083

Holliday, M. A., & Segar, W. E. (1957). The maintenance need for water in parenteral fluid therapy. Pediatrics, 19(5), 823–832.

National Council of State Boards of Nursing. (2026). 2026 NCLEX-RN test plan. https://www.nclex.com/test-plans.page