Treatment of chronic hyponatraemia
Firstly, if possible identify and treat the cause.
Aim to correct the hyponatraemia slowly. Too rapid correction will lead to shrinkage of brain cells. However more rapid correction may be needed if symptoms are serious e.g. coma or seizures. In this circumstance:
- Give hypertonic saline to raise plasma sodium concentration to a level at which seizures cease - usually a rise of around 5 mmol/l.
- Do not let the plasma sodium concentration rise by more than 8 mmol/l in any 24 hour period.
Gradual correction
- Raise plasma sodium by no more than 8 mmol/l/day to prevent development of osmotic demyelination syndrome.
- Reduce rate of correction further if patient may have deficiency of potassium or organic osmolytes eg malnutrition, catabolic states.
- Cells have an excess of EFW so they must lose EFW:
- Reduce intake of water
- Produce water loss independent of ADH eg diuretics + electrolyte replacement
- Reduce ADH levels
- Correct the low “effective” circulating volume
- Return the composition of the ECF to normal
- This will require the provision of adequate amounts of sodium in order to maintain ECF volume as EFW is lost.
- There must be a positive balance for Na+
- Return the composition of the ICF to normal
- This will require replacement of potential deficiencies of potassium and organic osmoles to the brain cells. Administration of KCl will lead to replacement of potassium for sodium in the ICF and an increase in sodium in the ECF with an increase in ECF volume. If the ECF volume was normal, the final step is to obligate the excretion of the extra ECF volume as “isotonic to the patient” NaCl.
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