Chapter 16: Disorders of Serum Sodium Concentration in the Elderly Patient

Disorders of serum sodium concentration are the most common electrolyte abnormalities seen in the geriatric population.1 Furthermore, the development of serum sodium abnormalities is associated with increased morbidity and mortality in affected patients.2 Often, however, the severity of the primary process contributing to the development of the abnormal serum sodium is responsible for the unsatisfactory outcome. The most common disorder of serum sodium concentration in the geriatric population is hyponatremia. Factors contributing to the development of hyponatremia in the elderly include age-associated decreases in GFR and free water clearance, as well as sodium losses from decreased activity of the renin-angiotensin-aldosterone system and increased activity of natriuretic hormones. The latter, however, may reflect the early development of fluid retention as may occur with excessive sodium intake from processed foods or subclinical cardiac disease. In addition, studies have suggested increased vasopressin activity in some elderly patients. Patients in outpatient settings exhibit hyponatremia in about 5% of those tested, with occurrence rates increasing to as high as 20% in hospitalized geriatric patients and 30% in patients seen in intensive care units.3 The most common cause of hyponatremia in this population involves abnormalities of secretion of the pituitary hormone arginine vasopressin (AVP), also called antidiuretic hormone (ADH).