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Dilutional Hyponatraemia — SCE Medical Oncology MCQ

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HardOncological EmergenciesDilutional HyponatraemiaSCE Medical Oncology

A 55-year-old man receiving cisplatin-based chemotherapy develops new-onset seizures. His serum sodium is 112 mmol/L. He has been drinking excessive water (>5 L/day) to 'flush the chemotherapy'. What has occurred?

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Correct answer: A — Severe dilutional hyponatraemia from excessive water intake compounded by cisplatin-induced renal salt wasting — management requires urgent hypertonic saline (carefully, max correction 10 mmol/L per 24 hours) and fluid restriction

Patients on cisplatin are often advised to maintain good hydration, but excessive free water intake (>3-4 L/day) can cause dangerous dilutional hyponatraemia, especially when compounded by cisplatin-induced renal salt wasting or SIADH. Seizures at Na 112 mmol/L represent a medical emergency. Management: IV hypertonic saline (3%) to raise Na by 1-2 mmol/L per hour initially (max 10 mmol/L per 24h to prevent osmotic demyelination syndrome), fluid restriction and identification/treatment of the contributing factors.

Reference: ESMO Oncological Emergencies; BNF; NICE; Sterns et al NEJM 2015