Age-Associated Abnormalities of Water Homeostasis

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Key points

  • Alterations in the regulation of water homeostasis in the elderly result from multiple consequences of aging including changes in body composition, diminished renal function, and alterations in hypothalamic-pituitary regulation of thirst and secretion of arginine vasopressin.

  • As a result of these multiple changes, the elderly have an increased frequency and severity of hypoosmolality and hyperosmolality, manifested by hyponatremia and hypernatremia as well as hypovolemia and hypervolemia.

  • The

Physiologic overview of disturbances of water metabolism

The ratio of solute content to body water determines the osmolality of body fluids, including plasma. As the most abundant extracellular electrolyte, the serum sodium concentration ([Na+]) is the single most important determinant of plasma osmolality under normal circumstances. Although the regulation of water and sodium balance is closely interrelated, it is predominantly the homeostatic control of water, rather than of sodium, that determines serum [Na+], and therefore plasma osmolality. On

Clinical overview of hyponatremia

Hyponatremia is the most common electrolyte disorder encountered in clinical practice.4 Such hyponatremia becomes clinically significant when accompanied by plasma hypoosmolality. When hyponatremia is defined as a serum [Na+] level of less than 135 mmol/L, the inpatient incidence is reported to be between 15% and 22%. Studies that define hyponatremia as serum [Na+] of less than 130 mmol/L demonstrate a lower, but still significant, incidence of 1% to 4%.5 Determination of a true incidence and

Clinical implications of hyponatremia

Hyponatremia is a strong independent predictor of mortality, reported to be as high as 60% in some series.14, 15 Recent data have confirmed that hyponatremia in the elderly population is associated with multiple clinically significant outcomes with regard to neurocognitive effects and falls,16 osteoporosis,17 incidence of bone fractures,18 and hospital readmission and need for long-term care.19

Terzian and colleagues15 studied the occurrence of admission hyponatremia and its association with

Clinical overview of hypernatremia

Hypernatremia necessarily reflects an increase in plasma osmolality. Cross-sectional studies of both hospitalized elderly patients and elderly residents of long-term care facilities show incidences of hypernatremia that vary between 0.3% and 8.9%.6, 14 Though a common presenting diagnosis in the elderly, 60% to 80% of hypernatremia in elderly populations occurs after hospital admission.14 By the same token, up to 30% of elderly nursing home patients experience hypernatremia following hospital

Mechanisms involved with disturbances of water metabolism in the elderly

Alterations in the regulation of water homeostasis in the elderly result from multiple consequences of aging: changes in body composition, alterations in renal function, and changes in hypothalamic-pituitary regulation of thirst and AVP secretion (Box 1). The cumulative effect of these changes is a diminution of homeostatic reserve, as well as loss of appropriate corrective responses to environmental and metabolic stressors.29, 30 Each of these potential mechanisms is considered separately,

Integration of changes in AVP secretion, thirst, and kidney function with aging

Beck’s conceptualization of “homeostatic inelasticity” aptly describes the consequences of the spectrum of physiologic changes that occur with aging.28 Aging causes distinct changes that affect normal water homeostasis at several discrete locations along the neurorenal axis responsible for maintaining normal water balance. As a result of these changes, the elderly experience a loss of homeostatic reserve to compensate for both decreases and increases in body fluids and osmolality. The net

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      Citation Excerpt :

      Chronic hyponatremia ([Na+] <135 mmol/l) is frequently caused by medication use (e.g., diuretics, antidepressants, and seizure medications), and chronic co-morbid conditions (e.g., liver, kidney or heart disease). In addition, at least one third of cases are due to the syndrome of inappropriate antidiuretic hormone secretion (SIADH), caused by inappropriate arginine vasopressin (AVP) secretion (Cowen et al., 2013). This electrolyte abnormality is a significant public health problem due to its high prevalence in elderly patients with associated morbidity and mortality.

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