Pediatric Dehydration: Assessment & Management

1. Background

• Total body water (TBW) = ~75% of body weight in infants, ~60% in older children
• Higher surface area-to-volume ratio increases insensible losses
• Inability to self-hydrate and communicate thirst

2. Assessment

Clinical Severity Classification

Key formula: % Dehydration = (fluid deficit / pre-illness weight) × 100% 1% dehydration = 10 mL/kg fluid deficit

• The Harriet Lane Handbook, p. 390

Validated Scoring: Clinical Dehydration Scale (CDS)

Investigations

• Mild-moderate with clear cause (e.g., viral gastroenteritis): usually none required
• Check electrolytes + BGL in:
  • Severe dehydration
  • Persistent vomiting/diarrhea >5 days
  • Suspected hypernatremic or hyponatremic dehydration
  • Altered mental status, seizures
  • Clinical concern for non-GI cause

3. Fluid Calculations

Maintenance Fluids - Holliday-Segar Method

• The Harriet Lane Handbook, p. 389

Deficit Replacement

• Fluid deficit (L) = pre-illness weight (kg) - current weight (kg)
• If premorbid weight unavailable, use clinical % dehydration × weight × 10 mL/kg

Replacement of Ongoing Losses

• Each watery stool: 10 mL/kg
• Each vomiting episode: 2 mL/kg

4. Treatment by Severity

Mild Dehydration (<5%)

• Oral Rehydration Therapy (ORT) - first-line (WHO and AAP recommendation)
• Encourage continued breastfeeding/age-appropriate diet
• ORS volume: 30-50 mL/kg over 3-4 hours
• Give in small sips: 5 mL every 1-2 minutes to minimize vomiting
• Replace ongoing losses concurrently
• No need for IV access routinely

Moderate Dehydration (5-9%)

• ORT is still preferred if tolerated (WHO, AAP)
• ORS volume: 60-80 mL/kg over 3-4 hours; replace 25% per hour
• Consider nasogastric (NG) tube if the child refuses fluids or cannot drink
• If ORT trial fails after 4-8 hours in the ED → admit for IV hydration
• Ondansetron (0.15 mg/kg PO/IV) can be used to facilitate ORT by reducing vomiting

Severe Dehydration (≥10%) / Shock

1. IV or intraosseous (IO) access immediately
2. Isotonic fluid bolus: 20 mL/kg of 0.9% NS or Lactated Ringer's over 15-30 minutes
3. Reassess after each bolus; repeat 20 mL/kg as needed until hemodynamic improvement
4. If >60 mL/kg required without improvement, consider septic shock, hemorrhage, capillary leak, or adrenal insufficiency
5. After resuscitation: complete deficit + maintenance replacement over 24 hours (isotonic fluid per AAP recommendations for isonatremic dehydration)
6. Monitor serum glucose and electrolytes closely

• Rosen's Emergency Medicine, p. 3112
• The Harriet Lane Handbook, p. 393

5. Oral Rehydration Solutions - Composition Comparison

• The Harriet Lane Handbook, p. 393

6. Special Electrolyte Scenarios

Isonatremic Dehydration (Na 130-150 mEq/L) - Most Common

• Replace with isotonic fluids (0.9% NS or LR)
• Deficit + maintenance over 24 hours

Hyponatremic Dehydration (Na <130 mEq/L)

• Correction too rapid → osmotic demyelination syndrome
• Raise Na by no more than 0.5 mEq/L/hr (max 10-12 mEq/L over 24 hr)
• Use isotonic saline; hypertonic saline (3% NaCl) only for symptomatic severe hyponatremia (seizures)

Hypernatremic Dehydration (Na >150 mEq/L)

• Correction too rapid → cerebral edema and seizures
• Lower Na by no more than 0.5 mEq/L/hr (max 10-12 mEq/L over 24 hr)
• Replace deficit slowly over 48-72 hours with hypotonic fluids
• Frequent neurological monitoring

7. Three-Phase Approach to IV Fluid Replacement

8. Antiemetics in Pediatric Rehydration

• Ondansetron (5-HT3 antagonist): 0.15 mg/kg PO/IV - evidence-based, reduces IV fluid need, reduces ED length of stay
• Antiemetics facilitate ORT and reduce IV access rates
• Routine fasting during infectious diarrhea is not recommended - early refeeding improves gut recovery

9. When to Admit / Refer

• Severe dehydration not responding to initial fluid boluses
• Electrolyte abnormalities requiring close monitoring
• Suspected surgical cause (intussusception, appendicitis, obstruction)
• Failed ORT after 4-8 hours
• Age <3 months
• Altered mental status, seizures
• Immunocompromised child
• Unable to ensure safe follow-up

10. Key Principles Summary

• ORT is the preferred treatment for mild-to-moderate dehydration - it is cheaper, safer, and equally effective as IV therapy for most children
• Weight loss percentage is the most accurate dehydration measure; use clinical signs when unavailable
• Isotonic fluids are the current standard for IV resuscitation and deficit correction in isonatremic dehydration
• Dysnatremic dehydration requires slow correction to avoid CNS complications
• Early refeeding (within 4-6 hours of rehydration) should be encouraged
• Avoid fruit juices, sports drinks, and hypotonic/hypertonic fluids for rehydration

Sources: The Harriet Lane Handbook (23rd ed.), pp. 389-393 | Rosen's Emergency Medicine, pp. 3105-3112 | Tintinalli's Emergency Medicine, pp. 263-272 | Textbook of Family Medicine (9th ed.), pp. 1287-1317 | StatPearls: Pediatric Dehydration (NCBI Bookshelf) | Royal Children's Hospital Melbourne Clinical Practice Guidelines