What are the clinical signs and management of dehydration?

Clinical Signs of Dehydration

Dehydration assessment requires distinguishing between two distinct types: water-loss (hypertonic) dehydration and volume depletion (isotonic) from fluid and electrolyte losses, each with different clinical presentations and diagnostic approaches. 1, 2

Key Diagnostic Principle

Serum or plasma osmolality >300 mOsm/kg is the gold standard for diagnosing water-loss dehydration in adults, particularly older adults. 1, 2 Calculated osmolarity >295 mmol/L can be used as a screening threshold when direct measurement is unavailable. 1

Clinical Signs by Type of Dehydration

Volume Depletion (Following Blood Loss, Vomiting, or Diarrhea)

For volume depletion after excessive blood loss: 1, 3

• Postural pulse change ≥30 beats per minute from lying to standing (97% sensitive, 98% specific when blood loss ≥630 mL) 1, 3
• Severe postural dizziness resulting in inability to stand 1, 3
• Note: Postural hypotension adds little additional predictive value beyond pulse changes 1
• Beta-blockers may reduce sensitivity and specificity in older adults 1, 3

For volume depletion after vomiting or diarrhea, a person with at least 4 of these 7 signs likely has moderate to severe dehydration: 1, 2, 3

• Confusion 1, 3
• Non-fluent speech 1, 3
• Extremity weakness 1, 3
• Dry mucous membranes 1, 2, 3
• Dry tongue 1, 2, 3
• Furrowed tongue 1, 2, 3
• Sunken eyes 1, 2, 3

Additional Signs in Infectious Diarrhea

For patients with dehydrating diarrhea, assess these volume depletion indicators: 1, 2

• Thirst (early warning sign) 1, 2
• Tachycardia 1
• Orthostatic vital sign changes 1
• Decreased urination 1
• Lethargy 1
• Decreased skin turgor 1
• Altered sensorium 1

Critical Pitfall: What NOT to Use

Simple clinical signs such as skin turgor, mouth dryness, weight change, urine color, or specific gravity should NOT be used to assess hydration status in older adults—they have been shown to lack diagnostic utility. 1 A Cochrane systematic review found none of these signs consistently useful for indicating hydration status in older adults. 1

Bioelectrical impedance should NOT be used to assess hydration status in older adults as it has not been shown to be usefully diagnostic. 1

Severity Classification

Categorize dehydration severity by fluid deficit percentage: 3

• Mild: 3-5% fluid deficit (increased thirst, slightly dry mucous membranes) 3
• Moderate: 6-9% fluid deficit (loss of skin turgor, dry mucous membranes) 3
• Severe: ≥10% fluid deficit (severe lethargy/altered consciousness, prolonged skin tenting) 3

Management Approach

Adults with mild, moderate, or severe volume depletion should receive isotonic fluids orally, nasogastrically, subcutaneously, or intravenously. 1, 3

For water-loss dehydration (osmolality >300 mOsm/kg): 1

• Mild cases: Encourage oral intake of preferred beverages (tea, coffee, juice, water—NOT oral rehydration solution or sports drinks) 1
• Moderate to severe or appearing unwell: Offer subcutaneous or intravenous hypotonic fluids in parallel with encouraging oral intake 1

For volume depletion from diarrhea: 4

• Reduced osmolarity oral rehydration solution (<250 mmol/L) is first-line therapy 4
• Dosing: 50-100 mL/kg over 2-4 hours for mild to moderate dehydration 4
• Severe dehydration: Immediate IV rehydration with Ringer's lactate or normal saline boluses 3

Special Considerations for Older Adults

All older adults should be considered at risk of water-loss dehydration due to low intake. 2 The standard clinical signs have different and generally poor sensitivity and specificity in this population. 1, 3 Older adults and caregivers should request periodic serum osmolality assessment from healthcare providers rather than relying on fluid intake estimation alone. 1