Hyponatremia is the most common in-hospital electrolyte disorderthat a physician encounters. Its management has been the subjectof numerous studies and reviews. In patients with chronic heartfailure or cirrhosis, water retention, mediated by the vasopressinV2 receptor in the renal collecting tubule, is an initiallypositive defense against a decrease in cardiac output or thedilated splanchnic circulation in cirrhosis.1 The syndrome ofinappropriate antidiuretic hormone secretion (SIADH) is, ofcourse, another matter. Water retention in SIADH serves no physiologicpurpose, and hyponatremia may be serious enough to require emergencymeasures.
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