When sodium has been low for more than 48 hours, or for an unknown time, the brain has adapted, and a rapid rise risks osmotic demyelination. The usual safe ceiling is a rise of no more than 8 to 10 mmol/L in any 24 hours, lower in those at highest risk — alcohol use disorder, malnutrition, hypokalaemia or liver disease.
Over-correction often happens without any treatment once the cause is removed: stopping a thiazide, giving saline to a volume-depleted patient, or the brisk water diuresis that follows. A sudden rise in urine output is the warning sign.
- Check sodium every 4 to 6 hours in the first day of correcting significant hyponatraemia.
- Limit the rise to 8–10 mmol/L in 24 hours, and less in malnourished or alcohol-dependent patients.
- A sudden large urine output during correction signals a water diuresis and impending over-correction.
- If the limit is exceeded, seek senior or specialist advice about re-lowering the sodium.
Why it matters
The harm in chronic hyponatraemia often comes from the correction, not the low sodium.
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