When sodium has been low for more than 48 hours, or for an unknown time, the brain has adapted, and correcting too quickly risks osmotic demyelination. The usual ceiling is about 8 mmol/L in any 24 hours, and lower in high-risk patients: those with alcohol use disorder, malnutrition, hypokalaemia or liver disease.
Correction often overshoots without any active treatment, once the cause — a thiazide, vomiting, or low solute intake — is removed and the kidneys start passing dilute urine. Check sodium every four to six hours early on, and watch urine output; a sudden brisk diuresis is the warning sign.
- Aim for no more than about 8 mmol/L rise in 24 hours in chronic hyponatraemia
- Check sodium every four to six hours in the first day of correction
- Watch for a sudden large output of dilute urine, which signals overcorrection
- Take extra care in alcohol use disorder, malnutrition, hypokalaemia and liver disease
Why it matters
Overcorrection is the iatrogenic harm in hyponatraemia, and it often happens without any treatment being given.
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