Hypernatremia - Diagnosis and Management Summary
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Hypernatremia - Diagnosis and Management Summary

Free water loss in excess of NaCl loss, very rarely excess Na ingestion

Etiologies: impaired access to free water or impaired thirst; ↓ urinary concentrating ability or DI (↓ production or efficacy of ADH)

 • Renal losses: Uosm <700–800 → post ATN diuresis, osmotic diuresis, DI, rarely loop diuretic; elderly (↓ max concentrating ability)

 • Extrarenal losses: Uosm >700–800 → GI loss from NGT, vomiting, diarrhea, insensible losses, hypodipsia

Step-wise approach:

Calculate free water deficit = TBW x (Na / 140 – 1); TBW = IBW (kg) x 0.4 in ♀ or 0.5 in ♂; shortcut 70kg: FWD (liters) ≈ (Na-140)/3

1. Calculate rate of free water replacement using http://www.nephromatic.com/sodium_correction.php and provide as PO free water, NGT free water boluses (200-400mL Q6-8h), or IV D5W; may also need DDAVP for DI (in conjunction with Endocrine consult)

2. Monitor: Expected ↓ Na/L fluid = (Na serum – Na fluid) / (TBW +1), but actual response is variable so check Na frequently

3. Goal: correct no faster than 1-2 mEq/L/h to prevent cerebral edema (risk not as well characterized as for ODS)

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Account created for the MGH Internal Medicine Housestaff Manual "White Book" - https://stk10.github.io/MGH-Docs/WhiteBook-2019-2020.pdf

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