🧸 Pediatrics · Lesson 1 of 5 · 6 min
Pediatric Vital Signs and Dehydration Math
👶 A 10 kg toddler with vomiting and diarrhea now weighs 9.1 kg. That is not 'a little dehydrated'. That is 9% of body weight gone, and the exam wants you to call it moderate before the IV goes in.
💡 Key idea
Children run fast and compensate until they crash: tachycardia early, hypotension late. Weight loss grades dehydration; ORS for mild and moderate, 20 mL/kg isotonic bolus for severe.
🧠 Why it matters
Pediatric vital signs run faster when younger: infants about 100 to 160 beats and 30 to 60 breaths per minute, toddlers 90 to 140 and 24 to 40, preschoolers 80 to 120 and 22 to 34, school-age 75 to 120 and 18 to 30, adolescents approaching adult ranges. Children compensate well, so TACHYCARDIA is an early sign of trouble and HYPOTENSION is a late, ominous one. Assess DEHYDRATION by WEIGHT LOSS: mild 3 to 5%, moderate 6 to 9%, severe 10% or more, plus sunken fontanel and eyes, dry mucous membranes, absent tears, decreased skin turgor, capillary refill over 2 seconds, lethargy, and urine output below 1 mL/kg/hr or fewer than 6 wet diapers a day in an infant. Mild to moderate dehydration is treated with ORAL REHYDRATION SOLUTION in small frequent amounts (about 50 to 100 mL/kg over 4 hours); avoid plain water, juice, soda and sports drinks, which are the wrong mix of sugar and electrolytes. Severe dehydration or inability to keep fluids down requires an isotonic IV bolus of 20 mL/kg. Early refeeding with a normal diet is encouraged once rehydrated. Infants dehydrate faster than adults because of a higher body water percentage, immature kidneys and a higher metabolic rate.
🏥 In the real world
🍼 A mother gives her vomiting 8-month-old apple juice and water because 'he needs fluids'. The infant worsens. The nurse teaches oral rehydration solution by teaspoon every few minutes, which stays down, and counts wet diapers. By evening the fontanel is flat and the baby is making tears. The right fluid in the right amounts is the whole intervention.
📌 Takeaways
- Tachycardia is early; hypotension is late in children
- Weight loss: 3–5% mild, 6–9% moderate, 10%+ severe
- ORS in small frequent sips; severe gets a 20 mL/kg isotonic bolus
✅ Test yourself
An infant who weighed 8 kg last week now weighs 7.2 kg after three days of diarrhea. How should the nurse classify the dehydration?
- Severe
- Not dehydrated
- Mild
- Moderate
Answer: A · Severe
0.8 ÷ 8 = 10% weight loss, which is severe dehydration requiring IV fluids.
Which finding in a 2-year-old with gastroenteritis is the EARLIEST indicator of significant fluid loss?
- Unresponsiveness
- Absent peripheral pulses
- Blood pressure 70/40
- Heart rate 150 at rest
Answer: D · Heart rate 150 at rest
Tachycardia is the first compensatory sign; hypotension and altered consciousness are late signs of decompensated shock.
A parent asks what fluid to give a mildly dehydrated toddler. Which is the best recommendation?
- Plain water only
- Apple juice
- A sports drink
- Oral rehydration solution
Answer: D · Oral rehydration solution
Oral rehydration solution, given in small frequent amounts, has the correct balance of glucose and electrolytes; juice and sports drinks worsen diarrhea, and plain water replaces no electrolytes.
NCLEX-style questions, XP and streaks in the app. No sign-up needed.