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Severe symptomatic hypotonic hyponatraemia — MRCEM SBA MCQ

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HardResuscitation and critical illnessSevere symptomatic hypotonic hyponatraemiaMRCEM SBA

A 68-year-old man taking bendroflumethiazide has had three days of worsening headache, nausea and confusion. In the emergency department he has a generalised tonic–clonic seizure that stops after intravenous lorazepam. Ten minutes later he remains drowsy (GCS 11/15) but is maintaining his airway, breathing adequately and haemodynamically stable. Laboratory sodium is 112 mmol/L, measured serum osmolality is 242 mOsm/kg and glucose is 5.4 mmol/L. A free-flowing large-bore peripheral cannula is in place; 2.7% sodium chloride is immediately available, but central venous access is not. Which is the most appropriate management plan now?

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Correct answer: D — Infuse 150 mL of 2.7% sodium chloride over 20 minutes, with prompt sodium reassessment and critical-care review.

The low measured osmolality and normal glucose support true hypotonic hyponatraemia. A seizure at a sodium concentration of 112 mmol/L is a severe neurological manifestation; stopping the convulsion with lorazepam does not remove the need to treat the underlying emergency. UK adult guidance recommends an immediate 150 mL bolus of 2.7% sodium chloride over 20 minutes, followed by sodium reassessment, senior involvement and critical-care discussion. A suitable peripheral cannula can be used when waiting for a central line would delay treatment. The initial aim is symptom improvement with a controlled sodium rise, not rapid normalisation. ([apps.worcsacute.nhs.uk](https://apps.worcsacute.nhs.uk/KeyDocumentPortal/Home/DownloadFile/4442)) **A** may be appropriate for some patients with hypovolaemic hyponatraemia, but isotonic saline is not the priority in this patient with a seizure. **B** would be appropriate if convulsions recurred or persisted; they have stopped, and another benzodiazepine would not correct the sodium. **C** recognises the need for hypertonic saline but introduces a harmful delay: central access is preferable, not a prerequisite. **E** starts the right type of fluid but targets normalisation without the bolus-and-reassessment sequence, risking excessive correction. Sodium and neurological status require close monitoring after initial treatment. ([apps.worcsacute.nhs.uk](https://apps.worcsacute.nhs.uk/KeyDocumentPortal/Home/DownloadFile/4442))

Reference: Management of Hyponatraemia in Adult Inpatients (Approved 10 January 2025) — https://apps.worcsacute.nhs.uk/KeyDocumentPortal/Home/DownloadFile/4442 Management of Hyponatraemia in Adult Inpatients (Approved 10 January 2025) — https://apps.worcsacute.nhs.uk/KeyDocumentPortal/Home/DownloadFile/4442