Etiology and Epidemiology of Hyponatremia.

Hyponatremia is a frequently encountered clinical finding, and by far the most common disorder of electrolyte and water homeostasis throughout the world. Given the complex pathophysiology of hyponatremia as well as its clinical implications, which range from apparently asymptomatic presentations to life-threatening conditions, a comprehensive understanding of its possible causes and of the frequencies of occurrence of the various types of hyponatremia in distinct clinical settings is essential for successful disease management. In this chapter, the diverse etiologies of hyponatremia are summarized, explained, and classified according to the patients' extracellular volume status. An in-depth review of the existing literature on epidemiologic data on incidence and prevalence of hyponatremia is provided covering the general population as well as the patient groups with community-acquired and hospital-acquired hyponatremia. Selected clinical scenarios that are described in detail are: hyponatremia in the geriatric population, in the emergency department, in the postoperative state, and in the intensive care setting. Distinct diseases and circumstances that are often associated with hyponatremia are reviewed briefly, while a more detailed discussion is covered in later chapters.