Clinical Features of Hyponatraemia:
- Manifestations of hyponatraemia depend greatly on the rate of its
development. A very slowly progressive hyponatraemia can be
asymptomatic while acutely developing hyponatraemia could be
very serious. - With hyponatraemia, plasma will be hypotonic while cells
(especially brain cells) will be hypertonic. To achieve osmotic
equilibrium, water will move from plasma to cells with a consequent
cell oedema (brain oedema). - Plasma sodium concentrations above 120 mmol/L are usually well
tolerated, while the majority of patients will have severe cerebral
dysfunction once plasma sodium is below 110 mmol/L (lethargy,
anorexia, nausea, vomiting, confusion, disorientation, convulsions,
coma and even permanent brain damage).
Treatment of Hyponatraemia:
- In severe hyponatraemia, rapid correction with hypertonic saline is
contraindicated as it may lead to fatal central pontine myelinolysis. It
is wise to increase plasma sodium by only 5-10 mmol/Litre per 24
hours. This is achieved through the administration of loop-diuretic
and normal saline and in severe cases, small amounts (100-200 ml)
of hypertonic (double strength i.e. 300 mmol/L) saline may be
infused. - Correction of the underlying cause, in the overloaded patient water
restriction can be combined with loop-diuretics as furosemide and
sometimes salt supplements. - In SIADH, lithium or demeclocycline may be given to induce a renal
concentration defect.