Dehydration: Total Body Water Deficit – Mechanisms and Vulnerable Groups

Dehydration is a net negative fluid balance—loss exceeds intake—depleting both intracellular (ICF) and extracellular (ECF) compartments.

Physiologic Impact

• Impaired thermoregulation
• Reduced cardiac output/perfusion
• Electrolyte derangements (hypernatremia/hyponatremia)
• Renal hypoperfusion → AKI
• Cognitive/physical performance decline

High-Risk Groups

• Infants/children (high BSA:weight, limited reserves)
• Elderly (blunted thirst, polypharmacy, comorbidities)
• Chronic illness (DM, CKD, HF)
• Athletes/occupational heat exposure

Treatment

Oral rehydration (ORS) for mild/moderate; IV isotonic crystalloid for severe/shock. Replace deficits over 24h (acute) or 48h (chronic) to avoid cerebral edema.