Dehydration Risk in Older Adults

Physiological Changes Contributing to Dehydration Risk

Aging blunts two key protective physiological responses to inadequate fluid intake: thirst sensation and primary urine concentration by the kidney 1
Older adults have reduced total body water, providing a smaller fluid reserve compared to younger adults 1
Many older adults use medications such as diuretics and laxatives which increase fluid losses 1
Renal function is often poor in older adults, so renal parameters no longer accurately signal low-intake dehydration 3

Memory problems may cause older adults to forget to drink and forget that they haven't drunk (not being prompted by thirst) 1
Many older adults voluntarily reduce fluid intake due to continence concerns and fear of incontinence 1
Issues about getting to the toilet in time can also lead to reduced fluid intake 2
Loss of social drinking routines as social isolation increases can contribute to dehydration risk 1
Physical access to drinks can be challenging for older adults 1
Swallowing problems and dysphagia can limit fluid intake 1

Low-intake dehydration is common in older adults, especially those who are frail and vulnerable 4
High-quality cohort studies consistently show that older adults with raised serum osmolality (>300 mOsm/kg) have increased risk of mortality 5
Older adults with raised serum osmolality (>300 mOsm/kg) also have a doubled risk of 4-year disability 5

Directly measured serum or plasma osmolality is the primary indicator of hydration status 3
An action threshold of >300 mOsm/kg should be used to identify low-intake dehydration 5
When direct measurement is unavailable, calculated osmolarity can be used with the formula: osmolarity = 1.86 × (Na+ + K+) + 1.15 × glucose + urea + 14 (all in mmol/L) 6
Action threshold for calculated osmolarity is >295 mmol/L 3
Simple clinical signs (skin turgor, mouth dryness, urine color) should NOT be used to assess hydration status in older adults 6
Bioelectrical impedance should NOT be used to assess hydration status 6

All older persons should be considered at risk of low-intake dehydration and encouraged to consume adequate amounts of fluids 2
Regular screening for dehydration is recommended when older adults contact the healthcare system, experience unexpected clinical changes, or are malnourished or at risk of malnutrition 3

Relying solely on clinical signs without laboratory confirmation can lead to misdiagnosis 7
Failing to recognize dehydration due to the absence of typical signs in older adults 7
Assuming older adults will drink when thirsty, when their thirst sensation is actually impaired 1