Health Care Quality Special Reports

Managing Patients With SIADH- Associated Hyponatremia July 2010 Hyponatremia Strategy Eileen McCaffrey The syndrome of inappropriate antidiuretic hormone (SIADH) is the most common cause of euvolemic hyponatremia (Am J Med. 2007;120[11A]:S1–S21). Release of the antidiuretic hormone arginine vasopressin (AVP) causes water retention. In normal physiology, AVP release is suppressed, excess water is excreted, and urine is dilute when the plasma osmolality is low. Plasma sodium is the main component of plasma osmolality; therefore, low serum sodium should lead to AVP suppression. Increased plasma osmolality or low intravascular volume appropriately stimulates AVP release. AVP release in the absence of these stimuli, when effective osmolality falls below 275 mOsm/kg of water, is one of the diagnostic features of SIADH (see “Criteria for SIADH Diagnosis,” below; Clin J Am Soc Nephrol. 2008;3:1175– 1184; N Engl J Med. 2007; 356:2064– 2072). Both impaired water excretion (due to AVP-induced water retention) and excessive water intake are necessary to produce hyponatremia in SIADH (Am J Med. 2006;119 [7A]:S36–S42). Risk of hyponatremia due to SIADH rises with older age (N Engl J Med. 2007; 356:2064–2072). Age-related physiological changes may impair the ability to excrete excess water (Clin Geriatr. 2009;17[9]:34–39). The severity of hyponatremia related to SIADH may vary depending on the type of SIADH, said Bruce Berger, associate professor of medicine at Case Western Reserve University in Cleveland. If AVP level tends to be stable, then hyponatremia also tends to be stable as long as fluid intake is constant. If AVP levels swing wildly, then serum sodium levels also tend to be erratic. Diagnosis A variety of conditions can lead to SIADH, including certain malignancies, lung diseases (such as pneumonia, tuberculosis, respiratory failure associated with positive pressure breathing), central nervous system disorders (such as subdural hematoma, .... You must sign-in to read complete article. If you are not registered click here. Username: Forgot it? Password: Financial support for this Website is provided by Premier Healthcare Resource.

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