Endocrine Abstracts

SIADH is the commonest cause of hyponatraemia in hospital practice SIADH must be distinguished from hypovolaemic and hypervolaemic hyponatraemia, and a diagnosis of euvolaemic hyponatraemia is established, the main differential is between SIADH and glucocorticoid deficiency.

Not all cases of SIADH require active management. Drug induced SIADH usually responds to drug withdrawal, though active management may speed up return to eunatraemia if the drug has a long half life. Mild hyponatraemia which accompanies reversible conditions such as lobar pneumonia, often need no treatment other than treatment of the underlying condition. However, as evidence accumulates that hyponatraemia is associated with increased morbidity and mortality, interest has grown in the opportunity to reduce morbidity and mortality with active management.

Chronic hyponatraemia. The evidence base for the success of active management is sparse. Most clinical guidelines recommend fluid restriction (FR) as first line therapy, though the evidence base for success of therapy is limited. A number of parameters, such as urine osmolality > 500 mOsm/kg and Furst equation > 1 predict poor response to FR. Patients find FR difficult for long term treatment. Demeclocycline is unreliable, unlicensed, has no evidence base, and had significant side effects. Urea has a limited, poor quality evidence base, and there is no available compound for clinical use. Vasopressin receptor antagonists have the backing of well-designed prospective studies, and undoubted clinical efficacy, though the cost of therapy deters many clinicians.

Acute hyponatraemia. Acute symptomatic hyponatraemia is a medical emergency associated with high mortality which can be reduced substantially by active management. New guidelines have been altered to recommend an initial rise in plasma sodium of 4–6 mmol/l over the initial 4–6 hours, as opposed to a steady rise in plasma sodium; the use of bolus hypertonic saline compared with continuous infusion to achieve this goal will be discussed.