Pediatric Hypotonic Dehydration

Aka: Pediatric Hypotonic Dehydration, Hypotonic Dehydration Management in Children

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II. Definitions

  1. Pediatric Hypotonic Dehydration
    1. Pediatric Dehydration AND Serum Sodium < 130
    2. Occurs when gastrointestinal losses are replaced with water (or other hypotonic solutions)

III. Protocol: Example Case

  1. Weight: 35 kg Child
  2. Dehydration: 10%
  3. Serum Sodium: 120

IV. Protocol: Stabilization with Bolus Fluids (Phase I)

  1. See Pediatric Dehydration Management
  2. Give 20 ml/kg Normal Saline or Lactated Ringers over 10-15 minutes
  3. May repeat bolus until circulation stable
    1. May require up to 60 ml/kg within the first 1-2 hours

V. Protocol: Calculate Replacement and Replace Phase 1 Fluids

  1. Approach as per Pediatric Dehydration Management
  2. Deficit: 3500 - 700 ml (Replaced Phase 1)
  3. Maintenance: 4*10+2*10+1*15= 75 ml/h
    1. See Maintenance Fluid Requirements in Children
  4. Replacement of 2800 ml over 24 hours
    1. First 8 hours
      1. Total: 1400/8 ml/h + (maintenance 75 ml/h) for 8 hours
      2. Hourly: 250 ml/hour for 8 hours (2 Liters over 8h)
        1. NS delivers (154 meq/1000 ml)(250 ml/h) = 39 meq/h Sodium
    2. Next 16 hours
      1. Total: 1400/16 ml/h + (maintenance 75 cc/h) for 16 hours
      2. Hourly: 163 ml/hour for 16 hours (2.6L over 16h)
        1. NS delivers (154 meq/1000 ml)(163 ml/h) = 25 meq/h Sodium
  5. Replacement of 2800 ml over 48 hours
    1. First 16 hours
      1. Total: 1400/16 ml/h + (maintenance 75 ml/h) for 16 hours
      2. Hourly: 163 ml/hour for 16 hours (2.6 Liters over 16h)
        1. NS delivers (154 meq/1000 ml)(163 ml/h) = 25 meq/h Sodium
    2. Next 32 hours
      1. Total: 1400/32 ml/h + (maintenance 75 cc/h) for 32 hours
      2. Hourly: 118 ml/hour for 32 hours (3.78 L over 32h)
        1. NS delivers (154 meq/1000 ml)(118 ml/h) =18 meq/h Sodium

VI. Protocol: Calculate Sodium Deficit and Sodium Requirement

  1. Calculate Deficit
    1. Formula: 0.6 x (weight kg) x (135 - Serum Sodium)
      1. Where 0.6 is volume of distribution (per kg)
      2. Where 135 is the desired Serum Sodium
    2. Example: (0.6 x 35 kilograms) x (135-120) = 315 meq
  2. Add Maintenance
    1. Formula: 3 meq/kg/day x (weight kg)
    2. Example: 3 meq/kg/24h x 35 kg = 105 meq Sodium/24 hours
  3. Subtract Replacement given Phase 1
    1. Phase 1 Fluid bolus
      1. NS: 1000 ml contains 154 meq Sodium
      2. Example: 700 cc contains 108 meq Sodium
    2. Remaining Sodium Required: 315 - 108 = 207 meq

VII. Protocol: Choose Appropriate solution to replace Sodium deficit

  1. Available solutions
    1. Normal Saline contains 154 meq/L Sodium (typical replacement)
  2. Example: Replacement over 24 hours
    1. First 8 hours: Replace half Sodium deficit (104 meq)
      1. Maintenance Sodium requirement in 8 hours = 105*(1/3) = 35 meq
      2. Total Sodium requirement in 8 hours = 104 + 35 = 139 meq or 17 meq/h
      3. Sodium Requirements: NS at 118 ml/hour delivers 18 meq/h Sodium
      4. Fluid Requirements: NS at 250 ml/hour delivers 39 meq/h Sodium (calculated above)
    2. Next 16 hours: Replace half Sodium deficit (104 meq)
      1. Maintenance Sodium requirement in 16 hours = 105*(2/3) = 70 meq
      2. Total Sodium requirement in 16 hours = 104 + 70 = 174 meq or 11 meq/h
      3. Sodium Requirements: NS at 71 ml/hour delivers 11 meq/h Sodium
      4. Fluid Requirements: NS at 163 ml/hour delivers 25 meq/h Sodium (calculated above)
  3. Example: Replacement over 48 hours
    1. First 16 hours: Replace half Sodium deficit (104 meq)
      1. Maintenance Sodium requirement in 16 hours = 105*(2/3) = 70 meq
      2. Total Sodium requirement in 16 hours = 104 + 70 = 174 meq or 17 meq/h
      3. Sodium Requirements: NS at 118 ml/hour delivers 18 meq/h Sodium
      4. Fluid Requirements: NS at 163 ml/hour delivers 25 meq/h Sodium (calculated above)
    2. Next 32 hours: Replace half Sodium deficit (104 meq)
      1. Maintenance Sodium requirement in 32 hours = 104*(4/3) = 139 meq
      2. Total Sodium requirement in 32 hours = 104 + 139 = 243 meq or 8 meq/h
      3. Sodium Requirements: NS at 52 ml/hour delivers 8 meq/h Sodium
      4. Fluid Requirements: NS at 118 ml/hour delivers 18 meq/h Sodium (calculated above)

VIII. Protocol: Example Summary - 35 kg Child with hypotonic Dehydration

  1. Given the severe Hyponatremia on presentation, replacement over 48 hours appears safer
    1. When instead, replaced over 24 hours, initial 250 ml/h rate would supply double the Sodium requirement
    2. Delivering Fluid Replacement over 48 hours allows for slower, safer raising of Sodium
  2. Replacement over 48 hours
    1. First 16 hours: D5 NS with 20 KCl at 163 ml/hour delivers 25 meq/h Sodium
    2. Next 32 hours: D5 NS with 20 KCl at 118 ml/hour delivers 18 meq/h Sodium

IX. Labs: Monitoring

  1. Monitor Serum Sodium every 2-4 hours
  2. Raise Serum Sodium <= 8-12 mEq/L/24 hours (or <0.5 mEq/hour, <2 mEq in 4 hours)

X. Management: Special Circumstance - Hyponatremic Seizure

  1. Background
    1. Serum Sodium raised 5 meq/L with 6 ml/kg of 3% NaCl (513 meq/L)
  2. Protocol
    1. Give 3% NaCl at 3 to 5 ml/kg/hour until Seizure stops

XI. Resources

  1. Vega and Bhimji (2017) Pediatric Dehydration in Stat Pearls
    1. https://www.ncbi.nlm.nih.gov/books/NBK436022/

XII. References

  1. Walton (2020) Crit Dec Emerg Med 34(6): 3-9
  2. Canavan (2009) Am Fam Physician 80(7):692-6 [PubMed]

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