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Severe Hyponatraemia — RACP Adult Medicine MCQ

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ModerateEmergency MedicineSevere HyponatraemiaRACP Adult Medicine

A 60-year-old man with recently diagnosed lung adenocarcinoma develops sudden onset confusion with serum sodium of 108 mmol/L. Urine osmolality is 450 mOsm/kg and urine sodium is 80 mmol/L. He is euvolaemic. His symptoms include seizures. What is the most appropriate immediate management?

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Correct answer: B — IV 3% hypertonic saline

Acute, severely symptomatic hyponatraemia (seizures, reduced consciousness) with sodium <120 mmol/L requires emergent treatment with IV 3% hypertonic saline. The initial goal is to raise sodium by 4–6 mmol/L in the first few hours to treat cerebral oedema. The rate should not exceed 6–8 mmol/L in 24 hours to avoid osmotic demyelination. The underlying cause is SIADH from lung cancer. Tolvaptan may be used later for chronic SIADH.

Reference: eTG – 2025 – Endocrinology; European Hyponatraemia Guideline – 2014