Endocrine Abstracts (2011) 26 MTE13

Hyponatraemia

Chris Thompson


Academic Department of Endocrinology, Beaumont Hospital/RCSI Medical School, Dublin, Ireland.


Hyponatraemia is the commonest electrolyte abnormality in hospitalised patients, with a prevalence of 20–30% and particularly high incidence in neurosurgical, pulmonary, geriatric, intensive care and oncology units. Up to 6% of patients have severe hyponatraemia (plasma sodium <125 mmol/l). A wealth of data is available which indicates that severe hyponatraemia is associated with cerebral irritation, causing confusion, coma and seizures, and significant excess mortality. The rapidity of onset of hyponatraemia is equally important in determining the likelihood of cerebral symptoms and death. Recent papers have reported that in addition there is excess mortality in patients with mild/moderate hyponatraemia (125–135 mmol/l). In addition even mild hyponatraemia is associated with significant morbidity, including gait disturbances and falls, cognitive deficits, bone fractures and osteoporosis. The commonest cause of hyponatraemia is SIADH; it is important to distinguish SIADH from other forms of hyponatraemia, particularly hypovolaemic hyponatraemia, for instance diuretic-induced. Glucocorticoid deficiency also biochemically mimics SIADH and it is particularly important to diagnose in patients with neurosurgical conditions, in whom the cerebral insult can produce both SIADH and acute ACTH deficiency. Accurate diagnosis is essential to ensure that the correct treatment of hypoglycaemia is instituted, both for the underlying cause and the biochemical disturbance. SIADH is traditionally treated with water restriction, which patients find difficult to maintain, and which has unpredictable efficacy. Demeclocycline, the first line pharmaceutical agent, also has unpredictable action, and has side effects, such as hypernatraemia, liver and renal damage, and photosensitive skin rashes. A European licence was granted in 2009 for tolvaptan, the specific vasopressin V2 receptor antagonist, whose efficacy in treating hyponatraemia was demonstrated in the SALT-1 and SALT-2 trials. The potential use of V2 receptor antagonists will be discussed.

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