Severe symptomatic hyponatraemia — FFICM MCQ

Correct answer: C — Give controlled hypertonic saline boluses with close sodium monitoring

C: Give controlled hypertonic saline boluses with close sodium monitoring is correct because this is severe, acutely symptomatic hyponatraemia (seizure at Na 112 mmol/L with confirmed low osmolality, excluding pseudohyponatraemia). Subarachnoid haemorrhage predisposes to SIADH or cerebral salt wasting, both giving this picture, but the seizure makes it a neurological emergency regardless of cause. UK critical care practice mandates bolus 2.7 or 3 percent hypertonic saline (150 to 167 mL over 20 minutes, repeated if needed) with frequent sodium rechecks, targeting only a 5 mmol/L rise initially to abort seizures and limit cerebral oedema. The goal is symptom control, not normalisation, because overly rapid correction risks osmotic demyelination syndrome. Why the other options are wrong: E. Correct sodium rapidly to 140 mmol/L: rapid full correction to normal markedly raises the risk of osmotic demyelination; rise must be capped at no more than 10 mmol/L in 24 hours. A. Restrict fluid and wait 24 hours: fluid restriction treats chronic asymptomatic SIADH; delaying active correction in a seizing patient risks further seizures, coma or herniation. B. Give desmopressin as sole therapy: desmopressin is used reactively to prevent or reverse overcorrection after hypertonic saline, or alongside saline in cerebral salt wasting; alone it does not raise sodium acutely and cannot be sole treatment for a seizing patient. D. Start loop diuretic without sodium replacement: diuretics increase free water clearance but give no immediate osmotic correction, and without sodium replacement can worsen hyponatraemia acutely. Key point: Any seizure or severe neurological symptom from hyponatraemia is treated as an emergency with bolus hypertonic saline targeting a small controlled rise (about 5 mmol/L per bolus, maximum 10 mmol/L per 24 hours) with close monitoring, not rapid normalisation.

Reference: Royal Cornwall Hospitals NHS Trust, Management of Hyponatraemia Clinical Guideline (based on European Hyponatraemia Guideline): for seizures or reduced consciousness with acute hyponatraemia, give 150 mL of 2.7% hypertonic saline IV over 20 minutes, aiming for symptom improvement or a 5 mmol/L rise (not full correction), with sodium rechecks at 20 minutes then 6, 12, 24 and 48 hours, and a cap of no more than 10 mmol/L rise in 24 hours. https://doclibrary-rcht.cornwall.nhs.uk/DocumentsLibrary/RoyalCornwallHospitalsTrust/Clinical/EndocrineAndDiabetes/ManagementOfHyponatraemiaClinicalGuideline.pdf