Chapter outlines

PHYSIOLOGICAL BASIS

• Decrease in total body water by about 10–15% due to reduced lean body mass.
• A reduction in thirst perception due to central nervous system dysfunction controlling thirst.
• Progressive reduction in renal blood flow, glomerular filtration rate and loss of renal mass.
• Impaired renal ability to concentrate urine and conserve water makes older adults prone to dehydration.
• Significant increase in atrial natriuretic peptide (ANP) activity and reduction in renin and aldosterone serum concentrations. These hormonal changes lead to an impaired ability to retain sodium, causing a greater risk of developing hyponatremia and hypovolemia.

Why understanding dehydration in the elderly is important?

• Hypovolemia is a common fluid and electrolyte disorder in the elderly [6, 7], which affects about 20% to 30% of older adults [8].
• Dehydration is the most common cause requiring hospitalization in the elderly [9, 10].
• Dehydration in the elderly is associated with a longer stay in the hospital, increased health care costs, morbidity and mortality [11–13].
• Dehydration in the elderly can cause problems like acute confusion, constipation, urinary tract infections, kidney stones, exhaustion, and pressure ulcers [14–16]. Elderly patients with dehydration can have orthostatic hypotension leading to impaired brain perfusion and dizziness, causing an increased risk of falls and bone fractures [17].
• Timely aggressive fluid administration can improve clinical outcomes in dehydration [18].

Why are elderly patients being more prone to develop dehydration?

• Reduced total body water (TBW) as a portion of body weight, so the risk of dehydration even with a loss of less volume of fluids.
• Inability to access water due to physical limitations and lack of help.
• Inadequate water intake due to decreased thirst sensation and altered awareness or mental status [5].
• With aging, renal function and ability to concentrate urine and retain fluid decline [16].
• Among older people, the habit is drinking less water than younger people [19], and the daily fluid intake of older people is below the recommended daily requirement [16].
• Common medications for the elderly such as diuretics for hypertension, increase the risk of dehydration.

DIAGNOSIS OF DEHYDRATION

NORMAL FLUID REQUIREMENT

PREVENTION OF DEHYDRATION

MANAGEMENT

• To provide the maintenance need for fluids and to correct volume depletion, elderly patients should be given fluids, preferably orally or nasogastrically.
• Euvolemic patients who may be nothing by mouth (NPO) may need intravenous maintenance fluids. The maintenance intravenous fluid requirement is lesser in the elderly. Maintenance of intravenous fluids recommended by NICE guidelines is about 20–25 mL/kg/day in the elderly, while intravenous (IV) fluid requirement in an adult person is approximately 25–30 mL/kg/day [27].
• Elderly patients have low body weight and lesser total body water (about 45–50% of body weight in the elderly compared to 50–60% of body weight in adults), so prescribe the total volume of fluids carefully.
• Cardiac or renal impairment is common in these patients, so avoid prescribing large volumes without assessing the patient’s fluid status.

• Ringer’s lactate and normal saline are the most widely used IV fluids for resuscitation in hypovolemia and hypotension.
• Hypovolemia with hypernatremia due to water losses or poor intake needs supplementation of hypotonic fluid.
• In patients with diarrhea or metabolic acidosis, preferred IV fluids are balanced crystalloids like Ringer’s lactate.
• Normal saline is preferred in patients with vomiting, hypovolemic hyponatremia, and metabolic alkalosis.

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