The age-related increases in asymptomatic bacteriuria and urinary tract infections are almost certainly due to increased residual bladder volume and loss of protective factors in the normal anatomic structures. As the prostate gland grows with advancing age, benign prostatic hypertrophy causes urinary retention in men. Urinary incontinence is more prevalent in women. The kidney is more susceptible to the effects of medications, particularly nonsteroidal anti-inflammatory drugs, which can result in sodium and fluid retention and subsequent hypertension. Dehydration or volume depletion, which is increasingly more prevalent with advancing age, often accompanies acute infections and increases the morbidity of pneumonia or urinary tract infections.

Dehydration is the most common fluid and electrolyte disorder in the frail elderly, owing to decreased fluid intake and increased fluid losses. Vomiting and diarrhea are the most common causes of isotonic dehydration. Fever associated with delirium is the leading cause of hypertonic dehydration. Hypotonic dehydration is seen most commonly with overuse of diuretics. Signs and symptoms of dehydration are notoriously vague or absent. Serial weights are helpful to quantify fluid therapy. Orthostatic tachycardia and hypotension are important clinical findings. Perhaps the most useful clinical parameter is a history of having missed one or more meals. Laboratory tests should measure the electrolytes, osmolality, creatinine, and blood urea nitrogen levels; a blood urea nitrogen-to-creatinine ratio greater than or equal to 25 is suggestive of dehydration.

Anticipation and prevention are crucial. Adequate food intake should be maintained, with 30 mL of daily fluid intake per kg of body weight recommended. For an acute event, it is important to review any long-term medications, particularly diuretics, that may have contributed to dehydration and to define the ethically appropriate approach to future episodes. In terminally ill patients, death from dehydration becomes a natural event in which symptom-focused care relieves discomfort from dry mucous membranes.