The maintenance of plasma sodium in the healthy aged

Handling of water and electrolytes in the healthy old

“…7 However, as with other organs, the functional characteristic of the aged kidney is a slow response or sometimes a complete inability to adapt to situations of overload or restriction.…”

“…Failure of awareness of this effect of ageing on renal function and failure of timely replenishment of Na + and water deficits may lead to acute renal failure. 7,8 It is inappropriate to routinely restrict salt intake in the aged unless they suffer from illnesses managed in part by salt restriction, such as liver, heart and renal diseases, in which oedematous syndromes (other than malnutrition) and/or hypertension are manifest. Even under those circumstances it is advisable to periodically monitor plasma electrolytes, particularly if diuretics are a mainstay of the therapeutic regime.…”

“…Aged people on unrestricted diets of salt and water have lower aldosterone plasma levels and respond more slowly to salt restriction than healthy young people (Table 1). 7,9,10,11 The most common and life-threatening clinical consequence of this is the development of hyperkalaemia in circumstances where an older patient is treated with aldosterone blocking agents such as spironolactone, or angiotensin converting enzyme inhibitors (ACE inhibitors) and angiotensin receptor blocking (AII RB) agents, which diminish aldosterone secretion by blocking AII production or its actions, respectively. Elderly patients with cardiac failure or other co-morbidities treated with anti-aldosterone agents should be periodically investigated for blood potassium, and at least every 3 months if simultaneously treated with drugs interfering with the renin-angiotensin system such as ACE inhibitors or angiotensin II receptor blockers.…”

Salt and Water Homeostasis

“…In addition, a number of tumors either produce ADH or a similar acting peptide [43,44]. Asymptomatic hyponatremia is often present in the elderly [52], frequently resulting in the unsubstantiated overdiagnosis of SIADH [53]. The causes of the hyponatremia are most often not demonstrable [52], although a minority are due to SIADH associated with pharmacologic agents, pneumonia or intracranial lesions [53].…”

“…Asymptomatic hyponatremia is often present in the elderly [52], frequently resulting in the unsubstantiated overdiagnosis of SIADH [53]. The causes of the hyponatremia are most often not demonstrable [52], although a minority are due to SIADH associated with pharmacologic agents, pneumonia or intracranial lesions [53]. As the patients are usually asymptomatic, there is no need for active therapy (hypertonic NaCl) in such patients -fluid restriction is usually adequate [53].…”