What are the signs of dehydration in the elderly?

Signs of Dehydration in the Elderly

Serum osmolality is the gold standard for assessing dehydration in elderly patients, with a threshold of >300 mOsm/kg indicating dehydration, while traditional clinical signs like dry mouth and skin turgor are unreliable in this population. 1

Diagnostic Approach for Dehydration in Elderly

Gold Standard Assessment

• Directly measured serum or plasma osmolality >300 mOsm/kg is the most accurate indicator of low-intake dehydration in older adults 2
• When direct measurement is not available, calculated serum osmolarity using the equation: osmolarity = 1.86 × (Na+ + K+) + 1.15 × glucose + urea + 14 (all measured in mmol/L) with an action threshold of >295 mmol/L can be used as a screening tool 2, 1

Unreliable Clinical Signs

• Simple signs and tests commonly used to assess dehydration should NOT be used in older adults as they lack diagnostic accuracy: 2
  • Skin turgor 2, 1
  • Mouth dryness 2, 3
  • Weight change 2
  • Urine color or specific gravity 2, 3
• Bioelectrical impedance should NOT be used to assess hydration status in older adults 2

Volume Depletion Assessment (Different from Low-Intake Dehydration)

Volume depletion (extracellular dehydration) occurs following excessive losses of fluid and electrolytes and requires different assessment approaches:

Blood Loss Assessment

• Postural pulse change from lying to standing (≥30 beats per minute) is 97% sensitive and 98% specific when blood loss is at least 630 mL 2
• Severe postural dizziness resulting in inability to stand is another reliable indicator 2
• Note that beta-blockers may affect these measurements in older adults 2, 4

Fluid and Salt Loss Assessment (e.g., from vomiting or diarrhea)

• A person with at least four of the following seven signs likely has moderate to severe volume depletion: 2, 5
  • Confusion 2, 5
  • Non-fluent speech 2, 5
  • Extremity weakness 2, 5
  • Dry mucous membranes 2, 5
  • Dry tongue 2, 5
  • Furrowed tongue 2, 5
  • Sunken eyes 2, 5

Most Reliable Physical Signs

While most physical signs are unreliable in the elderly, some have better diagnostic value than others:

• Dry axilla has moderate sensitivity (44%) and excellent specificity (89%) for detecting dehydration 6
• Sunken eyes and delayed capillary refill time show relatively good specificity (83%) 6
• Low systolic blood pressure (<100 mmHg) may have utility for diagnosing water-and-solute-loss dehydration (diagnostic odds ratio = 14.7) 3

Laboratory Findings

• Elevated serum sodium concentration is significantly higher in dehydrated elderly patients compared to non-dehydrated patients 6
• Saliva osmolality has shown moderate diagnostic accuracy (area under ROC curve = 0.76) for distinguishing both dehydration types 3

Treatment Approach

For Low-Intake Dehydration

• For older adults with measured serum osmolality >300 mOsm/kg who appear unwell, subcutaneous or intravenous fluids should be offered in parallel with encouraging oral fluid intake 2, 1
• In mild dehydration, encourage fluid intake according to preference (tea, coffee, fruit juice, water, etc.) 2, 1
• Oral rehydration therapy and sports drinks are NOT indicated for low-intake dehydration 2, 1

For Volume Depletion

• Older adults with mild/moderate/severe volume depletion should receive isotonic fluids orally, nasogastrically, subcutaneously, or intravenously 2

Prevention Strategies

• All older persons should be considered at risk of low-intake dehydration 1
• Older persons and their informal carers may use appropriate tools to assess fluid intake, but should also request serum osmolality assessment periodically 2
• Ensure elderly people consume sufficient fluids (at least 1.7 liters every 24 hours) 7
• Encourage small amounts of fluids throughout the day rather than large amounts at once 7

Pitfalls and Caveats

• Assessment of fluid intake by care staff is often highly inaccurate, with studies showing poor correlation between staff-recorded and actual fluid intake (r = 0.122) 2, 1
• Staff assessments are often approximately 700 ml/day lower than actual intake 2
• In older adults, renal function is often poor, making renal parameters unreliable indicators of dehydration 2, 1
• Clinical judgment alone is highly fallible in assessing dehydration in older adults 2, 1
• Early diagnosis can be difficult because classical physical signs of dehydration may be absent or misleading in older patients 8