A 62-year-old man with small cell lung cancer presents with a seizure. Sodium is 116 mEq/L, he is clinically euvolaemic, urine osmolality is 480 mOsm/kg, urine sodium 65 mEq/L, and thyroid, adrenal, and renal function are normal. What is the immediate management priority?
- A Fluid restriction at 800 mL/day
- B A bolus of 3% hypertonic saline aimed at raising sodium 4 to 6 mEq/L ✓
- C Isotonic saline infusion at maintenance rate
- D Tolvaptan orally
Correct answer: B. A bolus of 3% hypertonic saline aimed at raising sodium 4 to 6 mEq/L
Explanation
Symptomatic severe hyponatraemia with seizures is an emergency requiring rapid partial correction with a 100 to 150 mL bolus of 3% saline, targeting a 4 to 6 mEq/L rise to abort cerebral oedema, while keeping total correction under 10 mEq/L in 24 hours to avoid osmotic demyelination. Fluid restriction takes days and suits asymptomatic SIADH. Isotonic saline can worsen hyponatraemia here because the kidney excretes the salt load while retaining electrolyte-free water. Vasopressin antagonists are avoided in the emergency setting.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.