Dehydration and Fluid Planning in a 2-Year-Old with Gastroenteritis
A 2-year-old, 12 kg, presents with 2 days of vomiting and watery diarrhea. He is irritable, has dry mucous membranes, a capillary refill of 3 seconds, heart rate 140/min, and a 5% weight loss from a visit 2 weeks ago. He has had 3 wet diapers in 24 hours. The emergency department gives a 20 mL/kg normal saline bolus over 30 minutes. Reassessment shows heart rate 128/min, improved capillary refill, and the child is now drinking sips of oral rehydration solution. The parent asks, 'Can we just go home? He hates the IV and pulls at it.' Labs show sodium 133 mEq/L, potassium 3.2 mEq/L, and bicarbonate 16 mEq/L.
1. Classify the dehydration and electrolyte picture, and calculate the fluid deficit and a reasonable rehydration plan. Show your reasoning.
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Classification: This is moderate isotonic dehydration with mild hypokalemia and a mild metabolic acidosis from diarrheal bicarbonate loss. Signs supporting moderate (5-9%) dehydration: irritability, dry mucous membranes, delayed capillary refill, tachycardia, decreased urine output, and a documented 5% weight loss. The serum sodium of 133 mEq/L is isotonic (135-145 is normal; 133 is only mildly low and does not represent true hyponatremic dehydration). Potassium 3.2 mEq/L is mildly low and will fall further with continued diarrhea and as fluids dilute the serum potassium.
Deficit calculation: 5% of 12 kg = 0.05 × 12 = 0.6 L (600 mL) total deficit. The 20 mL/kg bolus = 240 mL, so roughly 360 mL remains to be replaced.
Maintenance: use the Holliday-Segar method: 100 mL/kg for the first 10 kg + 50 mL/kg for the next 10 kg. For 12 kg: 1000 + 100 = 1100 mL/day (~46 mL/hr).
Plan:
- Replace the remaining deficit over 24-48 hours (about 15-20 mL/hr additional) plus maintenance (~46 mL/hr), and replace ongoing losses stool for stool (roughly 10 mL/kg per loose stool).
- If oral intake is adequate and improving, oral rehydration is preferred and the IV can be discontinued. If IV is continued, use an isotonic solution with potassium added once the child is voiding.
- Do not give a potassium bolus; replace gradually and only after confirming urine output.
- Recheck electrolytes and weight in 12-24 hours, and monitor for ongoing losses.
2. The parent wants to go home. What discharge criteria and counseling would you give, and what would make you recommend admission instead?
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Discharge criteria (all should be met):
- Tolerating oral rehydration solution in small, frequent amounts without vomiting.
- Adequate urine output (at least 3-4 wet diapers in 24 hours) and improving activity.
- Caregiver understands the plan and can return.
- Reliable follow-up within 24 hours and a working scale or access to one.
Counseling:
- Give 5-10 mL of oral rehydration solution every 1-2 minutes by spoon or syringe; small volumes are better tolerated than large bottles. Avoid juice, soda, and sports drinks - high sugar worsens osmotic diarrhea.
- Continue breastfeeding and age-appropriate diet; do not withhold food for prolonged periods.
- Zinc supplementation is recommended by WHO for children with diarrhea in many settings; discuss with the provider.
- Teach warning signs: no urine for 8 hours, sunken eyes, no tears, lethargy, persistent vomiting, blood in stool, or high fever.
- Emphasize hand hygiene to limit spread.
Reasons to admit instead:
- Failed oral challenge (vomiting everything) or inability to drink.
- Severe dehydration, lethargy, or ongoing large losses.
- Caregiver unable to provide oral rehydration or unreliable follow-up.
- Electrolyte abnormality requiring monitoring (e.g., worsening hypokalemia, acidosis, or seizures).
The child's improving heart rate and willingness to drink support a trial of oral rehydration with close follow-up, but the decision hinges on whether he can keep fluid down in the observation period, not on the parent's preference alone. Document the teaching and give written instructions.