Hypernatraemia is relatively rare, but can occur because of excessive consumption of salt, prolonged diarrhoea or dehydration. Symptoms include an intense thirst,hypertension, oedema, agitation and convulsions. Hypernatraemia,when associated with dehydration, is managed with oral or intravenous fluid replacement. Care must be taken if administering hypotonic fluids intravenously because there is a risk of making the blood relatively hypotonic, causing cerebral oedema.