Fluid and electrolyte homeostasis in the elderly: physiological changes of ageing and clinical consequences.

Characteristic of the normal ageing process are changes in the renal, hormonal and thirst regulatory systems involved in the control of sodium and water balance. In the presence of disease or drug use, the ageing changes put the elderly person at increased risk of either sodium retention or loss and of water retention or loss. Clinically, these alterations in water and sodium balance are commonly expressed as either hyponatraemia or hypernatraemia with central nervous system dysfunction as the symptomatic expression. Thus, the impaired homeostasis of the many systems affecting fluid balance in the elderly is readily influenced by many of the disease states and medications which are often present in the elderly with resultant adverse clinical consequences. Awareness of these age-associated circumstances can allow the physician to anticipate the impact of illnesses and drugs and to implement a rational approach to therapeutic intervention and management.