The aging kidney. Defending a delicate balance of fluid and electrolytes.

The aging kidney is characterized by reduced glomerular filtration rate, loss of tubular volume, and narrowed homeostatic control of water and electrolyte balance. It is unclear whether these physiologic changes represent normal aging or subclinical disease. With aging, there is an increased risk of hyper- or hypovolemia. Sluggish control of potassium concentration also makes hyperkalemia more common, particularly when the patient is using certain drugs. Water metabolism is particularly vulnerable in older patients, resulting in a frequent tendency toward dehydration and hyperosmolality. Understanding these limitations on fluid and electrolyte homeostasis can help the clinician recognize and prevent complications when caring for older patients.