Dehydration is a clinical state of water imbalance in which water is used up or lost from the body at a rate that is faster than it is replaced.1,2 Water can be lost from the body in a number of ways. Mild fluid loss (1 – 2% of body weight) is a common occurrence and is easily corrected by drinking water in response to thirst.3 Profuse sweating can occur during exercise or in hot conditions resulting in evaporation of the body’s water from the skin’s surface in an effort to regulate body temperature. If fluid lost through sweating is not replaced, it can lead to hypovolemia and more serious dehydration.1,4 Diarrhea and vomiting cause rapid fluid loss from the gastrointestinal tract and also leads to dehydration.1
Symptoms of hypovolemia include thirst, weakness, and postural dizziness and hypotension.1,3 When the volume of water within the blood vessels decreases, the blood pressure drops. The change in blood pressure is most pronounced with changes in position. This condition, called orthostatic hypotension, is defined as a drop in systolic blood pressure of 20 mm Hg or in diastolic blood pressure of 10 mm Hg upon standing.1
Elderly people are more prone to dehydration, in part because their perception of thirst and the need for fluid replacement is diminished.5–7 Fortes et al performed hydration assessments of 130 elderly patients admitted to an acute care setting or emergency room to identify clinical markers for dehydration.8 Forty percent of the patients were clinically dehydrated (plasma osmolality >295 mOsm/kg or blood urea nitrogen to creatinine ratio >20). Systolic blood pressure 100 mm Hg or lower was the only physical sign that accurately predicted clinical dehydration in these patients.
References
- Mount DB. Fluid and Electrolyte Disturbances. In: Jameson JL, Fauci AS, Kasper DL, Hauser SL, Longo DL, Loscalzo J, eds. Harrison’s Principles of Internal Medicine, 20e. New York, NY: McGraw-Hill Education; 2018.
- Akerman AP, Tipton M, Minson CT, Cotter JD. Heat stress and dehydration in adapting for performance: good, bad, both, or neither? Temperature 2016; 3 (3): 412-436.
- Armstrong LE, Kavouras SA, Walsh NP, Roberts WO. Diagnosing dehydration: blend evidence with clinical observations. Curr Opin Clin Nutr Metab Care 2016; 19 (6): 434-438.
- Manz F, Wentz A, Armstrong L. The importance of good hydration for the prevention of chronic diseases. Nutr Rev 2005; 63 (6 II): 3-6.
- Weinberg A, MD M. Dehydration: evaluation and management in older adults. JAMA 1995; 28 (2): 1552-1556.
- Rolls BJ, Wood RJ, Rolls ET, Lind H, Lind W, Ledingham JG. Thirst following water deprivation in humans. AJP Regul Integr Comp Physiol 1980; 239 (5): R476-82.
- Phillips PA, Rolls BJ, Ledingham JG, et al. Reduced thirst after water deprivation in healthy elderly men. N Engl J Med 1984; 311 (12): 753-759.
- Fortes MB, Owen JA, Raymond-Barker P, et al. Is this elderly patient dehydrated? Diagnostic accuracy of hydration assessment using physical signs, Urine, and saliva markers. J Am Med Dir Assoc 2015; 16 (3): 221-228.
