How do you diagnose and manage dehydration in adults, particularly in distinguishing between mild, moderate, and severe cases?

Diagnosing Dehydration Severity in Acute Gastroenteritis

For adults with AGE, diagnose dehydration severity by distinguishing between two fundamentally different types: volume depletion (from fluid/electrolyte losses) versus low-intake dehydration (from inadequate oral intake), as they require different diagnostic approaches and have distinct biochemical signatures. 1, 2

Understanding the Two Types of Dehydration

Volume Depletion (Most Common in AGE)

• Occurs with vomiting and diarrhea, presenting with normal or LOW serum osmolality 1, 2
• Results from loss of both water and electrolytes (sodium, potassium) 1
• This is what you're typically seeing in AGE patients 1

Low-Intake Dehydration

• Presents with ELEVATED serum osmolality (>300 mOsm/kg) 1, 2
• Results from inadequate fluid intake without proportional electrolyte loss 1
• Less common in AGE unless patient has been unable to drink for extended periods 1

Diagnostic Algorithm for Volume Depletion in AGE

Mild Volume Depletion

• Clinical signs are subtle and unreliable in mild cases 3
• Patient can maintain oral intake 1
• Minimal clinical findings 1

Moderate to Severe Volume Depletion

Use the validated 7-sign assessment tool: A patient with ≥4 of the following signs has moderate to severe volume depletion: 1

1. Confusion
2. Non-fluent speech
3. Extremity weakness
4. Dry mucous membranes
5. Dry tongue
6. Furrowed tongue
7. Sunken eyes

This combination has been specifically validated for volume depletion from vomiting/diarrhea and is far more reliable than individual clinical signs. 1

Severe Volume Depletion (Requires Immediate Resuscitation)

• Postural pulse change ≥30 beats/minute from lying to standing 1
• Severe postural dizziness preventing ability to stand 1
• Shock, altered mental status, or inability to tolerate oral intake 1

Critical Pitfall to Avoid

Do NOT rely on serum osmolality to diagnose volume depletion from AGE. 2 The European Society for Clinical Nutrition warns that volume depletion from diarrhea and vomiting is associated with normal or LOW plasma osmolality, not elevated osmolality. 1, 2 Elevated osmolality (>300 mOsm/kg) indicates low-intake dehydration, which is a physiologically distinct condition requiring different treatment. 1, 2

Do NOT confuse IVC collapsibility with dehydration assessment. 2 Simple clinical signs and ultrasound measures including IVC collapsibility have not been validated as reliable indicators and primarily reflect volume status rather than true dehydration. 2

Treatment Based on Severity

Mild to Moderate Volume Depletion

• First-line: Reduced osmolarity oral rehydration solution (ORS) 1
• Administer 100 mL/kg over 2-4 hours, then reassess 2, 4
• Nasogastric ORS may be used if patient refuses to drink or cannot tolerate oral intake 1

Severe Volume Depletion

• Immediate IV isotonic fluids (lactated Ringer's or normal saline) 1
• Continue until pulse, perfusion, and mental status normalize 1
• Switch to ORS once patient can tolerate oral intake 1

All Severity Levels

• Replace ongoing losses with ORS throughout illness 1
• Resume age-appropriate diet immediately after rehydration 1, 4
• Isotonic fluids (oral, NG, subcutaneous, or IV) are appropriate for all severity levels 1

When to Check Serum Osmolality

Only check serum osmolality if you suspect low-intake dehydration (patient unable to drink for extended period without proportional GI losses). 1, 2 In this scenario, osmolality >300 mOsm/kg confirms dehydration and indicates need for hypotonic fluid replacement if unable to drink. 1, 2

Practical Clinical Approach

1. Assess volume status using the 7-sign tool (≥4 signs = moderate-severe) 1
2. Check orthostatic vitals (≥30 bpm increase = severe) 1
3. Determine treatment route: oral ORS for mild-moderate, IV for severe 1
4. Do NOT wait for labs - clinical assessment drives initial management 1
5. Avoid antimotility agents in suspected inflammatory diarrhea or fever 1