Treatment

Rate and degree of correction

• In chronic hyponatraemia correction should not exceed 0.5 mmol/l/h in the first 24 h and 0.3 mmol/l/h thereafter.

• In acute hyponatraemia the ideal rate of correction is controversial though elevations in plasma Na + can be faster, but <20 mmol/l/day.

• A plasma Na+ of 125-130 mmol/l is a reasonable target for initial correction of both acute and chronic states. Attempts to achieve normo- or hypernatraemia rapidly should be avoided.

• Neurological complications, e.g. central pontine myelinolysis, are related to the degree of correction and (in chronic hyponatraemia) the rate. Premenopausal women are more prone to these complications.

Extracellular fluid (ECF) volume excess

• If symptomatic (e.g. seizures, agitation), and not oedematous, 100 ml aliquots of hypertonic (1.8%) saline can be given, checking plasma levels every 2-3 h.

• If symptomatic and oedematous, consider furosemide (10-20 mg IV bolus prn), mannitol (0.5g/kg IV over 15-20 min), and replacement of urinary sodium losses with aliquots of hypertonic saline. Check plasma levels every 2-3 h. Haemofiltration or dialysis may be necessary if renal failure is established.

• If not symptomatic, restrict water to 1-1.5 l/day. If hyponatraemia persists, consider inappropriate ADH (SIADH) secretion.

• If SIADH likely, give isotonic saline and consider demeclocycline.

• If SIADH unlikely, consider furosemide (10-20 mg IV bolus prn), mannitol (0.5 g/kg IV over 15-20 min), and replacement of urinary sodium losses with aliquots of hypertonic saline.

• Check plasma levels regularly. Haemofiltration or dialysis may be necessary if renal failure is established.

Extracellular fluid volume (ECF) depletion

• If symptomatic (e.g. seizures, agitation), give isotonic (0.9%) saline. Consider hypertonic (1.8%) saline.

• If not symptomatic, give isotonic (0.9%) saline.

General points

• Equations that calculate excess water are unreliable. It is safer to perform frequent estimations of plasma sodium levels.

• Hypertonic saline may be dangerous in the elderly and those with impaired cardiac function. An alternative is to use furosemide with replacement of urinary sodium (and potassium) losses each 2-3 h. Thereafter, simple water restriction is usually sufficient.

• Many patients achieve normonatraemia by spontaneous water diuresis.

• Use isotonic solutions for reconstituting drugs, parenteral nutrition, etc.

• Hyponatraemia may intensify the cardiac effects of hyperkalaemia.

• A true hyponatraemia may occur with a normal osmolality in the presence of abnormal solutes e.g. ethanol, ethylene glycol, glucose.

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