What it is
In hyponatremic dehydration the child is both volume- and sodium-depleted, with serum Na < 135 mEq/L. The danger is not the number itself but the speed of correction: raise serum Na too fast and you risk osmotic demyelination syndrome (central pontine myelinolysis). This tool deliberately makes the headline figure the safe 24-hour target, not the full deficit to 135 — because giving the whole deficit over a day is exactly the error that injures the brain.
Formula
The tool combines three pieces:
$$ Maintenance = Holliday\text{-}Segar\ (100/50/20\ \text{rule}) $$ $$ Deficit\ fluid\ (mL) = %dehydration \times weight,(kg) \times 10 $$ $$ Safe\ \Delta Na = \min(8,\ 135 - Na_{measured})\ \text{mEq/L per 24 h} $$
It also reports a theoretical total sodium deficit, (135 − Na) × 0.6 × weight, explicitly labelled “spread over DAYS” so it is never mistaken for a 24-hour order.
When to use
Symptomatic or asymptomatic hyponatremia with clinical dehydration, to plan maintenance + deficit fluids and to anchor the daily correction ceiling. Acute symptomatic hyponatremia (seizure, obtundation) is a separate emergency — hypertonic saline, not this calculation.
Worked example
A 12 kg child, serum Na 122 mEq/L, 8% dehydration:
- Maintenance (Holliday-Segar): 1000 + (12−10)×50 = 1100 mL/day
- Deficit fluid: 8 × 12 × 10 = 960 mL
- Total over 24 h: 2060 mL
- Safe ΔNa: min(8, 135−122) = +8 mEq/L → target Na ≤ 130
- Theoretical total deficit to 135: (135−122) × 0.6 × 12 = 93.6 mEq (over days, not 24 h)
The headline output is therefore “Max +8 mEq/L in 24 h → target Na ≤ 130” — not 93.6 mEq dumped in a day.
Safety: correction rate is the limit
- Raise serum Na ≤ 8 mEq/L per 24 h (≤ 4–6 in chronic or severe cases).
- Recheck Na every 2–4 h during active correction.
- If Na rises faster than the cap, stop and consider D5W ± desmopressin to re-lower.
- Symptomatic seizure/coma: 3% NaCl 2 mL/kg over 10–15 min (max ~100–150 mL/bolus), repeatable ×3, rechecking Na after each.
Pitfalls
- The deficit is a total, not a rate — the 24h ceiling governs the order.
- Autocorrection overshoot: once the ADH stimulus resolves, brisk aquaresis can blow past the cap; be ready with free water or DDAVP.
- Use isotonic (0.9% NaCl) maintenance per AAP 2018 — hypotonic maintenance fluids cause hospital-acquired hyponatremia.
- If 3% saline is unavailable, involve PICU; do not improvise hypertonic mixtures.
Run it: Hyponatremic Dehydration
Decision support for qualified clinicians only — verify against current primary guidelines and your clinical judgement.