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Hypernatraemia DI in ICU — FRCA Final MCQ

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ModerateIntensive Care MedicineHypernatraemia DI in ICUFRCA Final

A 70-year-old man in the ICU with sepsis develops hypernatraemia (Na⁺ 158 mmol/L). His urine output is 60 mL/hr with urine osmolality 150 mOsm/kg. He is not on diuretics. What is the most likely cause and appropriate fluid for correction?

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Correct answer: B — Diabetes insipidus – desmopressin and 5% dextrose or 0.45% saline

Hypernatraemia with polyuria and low urine osmolality (<300 mOsm/kg when serum osmolality is high) indicates diabetes insipidus (DI). In ICU, central DI can occur from brain injury, sepsis-related hypothalamic-pituitary dysfunction, or post-neurosurgery. Treatment: desmopressin (DDAVP) 1-4 mcg IV/SC for central DI, and free water replacement with 5% dextrose or 0.45% saline. Correction rate should not exceed 10-12 mmol/L per 24 hours to avoid cerebral oedema. If urine osmolality were >600 with low output, dehydration with appropriate renal concentration would be the cause.

Reference: NICE – 2017 – CG174 IV fluid therapy; ICS – 2023 – Electrolyte management in ICU