Dehydration

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.

• Insufficient water intake, particularly in elderly individuals and the critically ill
• Increased free water loss
  • Renal loss: diuretics, hyperglycemia, polyuric phase of renal failure, diabetes insipidus
  • Extrarenal loss: diarrhea , vomiting, burns, increased sweating, fever, inflammation, ascites
• See also hypovolemic hypernatremia and euvolemic hypernatremia.

References:^{[1][2][3][4][5]}

• Thirst
• Dry skin and mucous membranes
• Headache, dizziness, disorientation
• Weakness, fatigue, hemodynamic instability
• Dark circles around the eyes and frequent blinking (reduced tear fluid quantity)
• Children: no tears when crying
• Infants: sunken fontanelle, restlessness/lethargy

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)

References:^[3][4][6][7]

• Hypovolemic shock → prerenal renal failure
• Increased risk of infection, particularly of the urinary tract
• Thrombosis
• Osmotic demyelination syndrome
• Patients with diabetes mellitus: Dehydration can trigger diabetic ketoacidosis.

References:^{[16][17][18][19]}

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