Endocrine Abstracts

Hyponatraemia is the commonest electrolyte abnormality in acute hospital admissions. The presence of hyponatraemia is a negative prognostic factor which is associated with increased duration of hospital stay and increased mortality; mortality rates exceed 50% when plasma sodium concentration is <115 mmol/l. Errors in establishing the aetiology of hyponatraemia have been shown to lead to inappropriate treatment, with adverse outcomes, so accurate diagnosis is an essential prerequisite to correct management. There are a number of diagnostic alogorithms available for hyponatraemia, but a practical and logical approach is to establish the blood volume status by clinical, biochemical and cardiovascular parameters, which allows the identification of hypovolaemic, euvolaemic or hypervolaemic hyponatraemia. Diagnosis can be finessed by the measurement of urinary sodium concentration, which indicates whether appropriate antinatriuresis is occurring. The treatment of hyponatraemia is dependent on the aetiology; hypovolaemic hyponatraemia is dependent on intravenous saline replacement, whereas hypervolaemic hyponatraemia is usually treated with diuretics. Euvolaemic hyponatraemia is initially treated with water restriction, with demeclocycline therapy as second line. The new vasopressin antagonists, such as tolvaptan and conivaptan, which cause an aquaresis, without natriuresis, have been shown in trials to be valuable in the treatment of hypervolaemic and euvolaemic hyponatraemia. Consideration should also be given to the diagnosis of ACTH deficiency in any patient with hyponatraemia and intracranial disease, as steroid therapy can be life saving.