A 50 kg woman develops severe symptomatic hyponatremia (serum Na 112 mEq/L). Her estimated total body water (TBW) is 30 L. Using the sodium deficit formula, how many mEq of sodium are required to raise her serum sodium to 120 mEq/L?

• A 120 mEq
• B 360 mEq
• C 480 mEq
• D 240 mEq ✓

Explanation

Sodium deficit = TBW × (desired Na − current Na) = 30 × (120 − 112) = 30 × 8 = 240 mEq. Correction to 120 rather than 140 is intentional to avoid osmotic demyelination syndrome (ODS/central pontine myelinolysis): the recommended maximum correction rate is 8–10 mEq/L per 24 hours (some guidelines allow 10–12 mEq/L per 24 h only in very severe/symptomatic cases). Correcting beyond 120 in the first 24 hours risks ODS, particularly in chronic hyponatremia.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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