• Clinical science

Dehydration (Exsiccosis)


Dehydration (exsiccosis) is a state of decreased total body water. This decrease in total body water occurs in excess of sodium (also called “free water loss”), resulting in a hypertonic and hypernatremic state. The terms “hypotonic” and “isotonic” are sometimes incorrectly used to describe dehydration, but these terms are only associated with hypovolemia and hypovolemic shock. Dehydration most often affects children and the elderly. Treatment of dehydration involves correcting the free water deficit.



Clinical features

Clinical feature Mild dehydration Moderate dehydration Severe dehydration
Decrease in body weight < 3% 3–9%

> 9%

Symptoms Mental status Alert Restless, irritable Lethargic, confused
Thirst Slightly increased Thirsty; drinks eagerly Refuses to drink
Urine output Normal ↓ (dark concentrated urine) ↓↓
Signs specific to dehydration Eyes Normal Slightly sunken Significantly sunken
Tears (especially children) Normal Decreased Absent
Tongue Moist Dry Parched
Skin turgor Instant recoil Recoil within 2 seconds Recoil after 2 seconds; significant skin tenting
In infants: anterior fontanelle Normal Slightly sunken Significantly sunken
Signs of hypovolemia and hypovolemic shock Pulse rate Normal Mildly tachycardic Initially tachycardia → later bradycardia
Blood pressure Normal Normal; postural hypotension may be present Hypotension
Capillary refill time Normal (< 2 seconds) 2–3 seconds > 3 seconds
Extremities Warm Cool Mottled
Breathing Normal Tachypnea Tachypnea with deep breathing (Kussmaul breathing)



  • Serum sodium:
    • Hypernatremia
    • Serum sodium levels can be used to determine the amount of free fluid needed to correct dehydration (see treatment of hypernatremia).
  • Hematocrit
  • ↓ Serum bicarbonate levels
  • BUN to serum creatinine ratio > 20:1 → renal hypoperfusion due to hypovolemia
  • Urine osmolality: See sodium imbalance for more information.
    • < 800 mOmol/L → renal free water loss
    • > 800 mOmol/L → extrarenal free water loss
  • Blood glucose levels
    • Hypoglycemia → decreased fluid intake as a possible cause of dehydration
    • Hyperglycemiaosmotic diuresis as a possible cause of dehydration



Patient who are hypovolemic as a result of severe dehydration require immediate fluid resuscitation with crystalloid solutions.

  1. Fluid resuscitation
    • Severe hypovolemia
      • Children: rapid infusion of 20 mL/kg of isotonic saline → reassess → repeat as needed
      • Adults: rapid infusion of isotonic crystalloid → reassess → repeat as needed
    • Moderate hypovolemia
      • Children: consider oral hydration therapy or 10 mL/kg of isotonic saline → reassess → repeat as needed
  2. Correction of electrolyte abnormalities




We list the most important complications. The selection is not exhaustive.