Hyponatremic Dehydration (Na <130 mEq/L)

Here you calculate sodium deficit explicitly:$$\textbf{Na⁺ deficit (mEq)} = (135 – \text{Serum Na}) \times 0.6 \times \text{weight (kg)}$$Na⁺ deficit (mEq)=(135−Serum Na)×0.6×weight (kg)

👉 135 mEq/L is taken as desired Na

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Example

10 kg child, Na = 125 mEq/L$$(135 – 125) \times 0.6 \times 10 = 10 \times 6 = \textbf{60 mEq}$$(135−125)×0.6×10=10×6=60 mEq

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Important

• Correct slowly over 24–48 hrs
• Max rise: ≤8–10 mEq/L/day
• Give via DNS / NS + added Na as needed

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Isonatremic Dehydration (Na 130–150)

No sodium deficit calculation needed

Instead calculate:

• Fluid deficit = % dehydration × weight × 10

Example:

• 10% dehydration in 10 kg child →
  = 10 × 10 × 10 = 1000 mL deficit

Give:

• Deficit + maintenance + ongoing loss
• Usually NS / RL initially

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Hypernatremic Dehydration (Na >150)

👉 Do NOT calculate sodium deficit
Instead calculate free water deficit:$$\textbf{Water deficit (L)} = 0.6 \times \text{wt} \times \left(\frac{\text{Na}}{145} – 1\right)$$Water deficit (L)=0.6×wt×(145Na​−1)

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Example

10 kg child, Na = 160$$0.6 \times 10 \times (160/145 – 1) \approx 6 \times 0.103 = \textbf{0.62 L}$$0.6×10×(160/145−1)≈6×0.103=0.62 L

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Key Pediatric Pearls (Exam Gold)

• Hyponatremia → calculate Na deficit
• Hypernatremia → calculate water deficit
• Isonatremia → calculate fluid deficit only

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Correction Rules

• Hyponatremia: ↑ Na ≤8 mEq/day
• Hypernatremia: ↓ Na ≤10–12 mEq/day
• Rapid correction → ODS (hypo) / cerebral edema (hyper)