How do you calculate maintenance and deficit fluids for a pediatric patient with severe dehydration due to gastroenteritis?

Calculating Maintenance and Deficit Fluids for Pediatric Severe Dehydration

For pediatric patients with severe dehydration due to gastroenteritis, calculate maintenance fluids using the Holliday-Segar method and estimate deficit based on clinical assessment of dehydration percentage (typically 10% or more of body weight in severe cases), then administer isotonic crystalloid boluses of 20 mL/kg until perfusion normalizes before transitioning to deficit replacement. 1, 2

Step 1: Assess Severity of Dehydration

Determine the degree of dehydration based on clinical signs:

• Severe dehydration (≥10% fluid deficit):
  • Altered mental status/lethargy
  • Prolonged skin tenting (>2 seconds)
  • Cool, poorly perfused extremities
  • Decreased capillary refill
  • Rapid, deep breathing (acidosis)
  • Weak or absent pulses 1, 2

Step 2: Calculate Maintenance Fluid Requirements

Use the Holliday-Segar method:

• First 10 kg: 100 mL/kg/day
• Second 10 kg: 50 mL/kg/day
• Each additional kg: 20 mL/kg/day

Example calculation:

• For a 20 kg child: (10 kg × 100 mL) + (10 kg × 50 mL) = 1500 mL/day
• Divide by 24 for hourly rate: 1500 ÷ 24 = 62.5 mL/hour

Step 3: Calculate Deficit Fluid Requirements

• Estimate fluid deficit: Weight (kg) × % dehydration
• For severe dehydration, assume 10% deficit
• Example: 20 kg child with severe dehydration = 20 kg × 0.10 = 2000 mL deficit

Step 4: Administer Rehydration Therapy

Initial Resuscitation Phase (First 1-2 hours)

• For severe dehydration: Administer IV boluses of isotonic crystalloid (Lactated Ringer's or normal saline) at 20 mL/kg
• Continue boluses until pulse, perfusion, and mental status normalize 1, 2
• This may require 60-80 mL/kg in the first hour for severe cases

Deficit Replacement Phase (Next 24 hours)

• After initial stabilization, replace the remaining deficit over 24 hours
• Calculate: Remaining deficit + maintenance requirements + ongoing losses
• Administer 50% of the remaining deficit in the first 8 hours and the rest over the next 16 hours 2

Maintenance Phase

• Once rehydrated, continue maintenance fluids
• Replace ongoing losses with ORS:
  • For children >10 kg: 120-240 mL ORS for each diarrheal stool or vomiting episode
  • For children <10 kg: 60-120 mL ORS for each episode 1

Step 5: Monitor and Adjust

• Reassess hydration status frequently
• Monitor vital signs, urine output, mental status
• Adjust fluid rates based on clinical response
• Transition to oral rehydration when the patient is alert and can tolerate oral intake 1, 2

Common Pitfalls to Avoid

• Underestimating severity: Delayed IV therapy in severe dehydration can increase mortality
• Neglecting ongoing losses: Continue to replace stool and emesis losses throughout treatment
• Inappropriate fluids: Don't use hypotonic solutions for initial resuscitation in severe dehydration
• Delayed transition to oral rehydration: Switch to oral rehydration as soon as clinically appropriate 2

Special Considerations

• For malnourished infants, consider smaller-volume, frequent boluses (10 mL/kg) due to reduced cardiac output capacity 1
• Laboratory tests are rarely needed but may help in severe cases; BUN and bicarbonate levels can help confirm severity of dehydration 3
• Once the patient is stabilized, resume age-appropriate normal diet every 3-4 hours 1