• Dehydration is a pathologic state of negative fluid balance in the body. Severity is generally expressed as a percentage of body weight. Mild, moderate, and severe dehydration correspond to volume loss of <5%, 5–10%, and >10%, respectively.
  • Dehydration can also be classified as isotonic (Sodium [Na] 130 to 150 mmol/L), hypotonic (Na <130 mmol/L), or hypertonic (Na >150 mmol/L).
  • Dehydration can be the result of a wide range of illnesses.
  • Accurate clinical recognition and classification of dehydration determines rehydration treatment options.


  • Globally, dehydration from diarrheal illness is one of the leading causes of mortality in children <5 years old.
  • Incidence of moderate to severe dehydration in the United States has declined since the introduction of routine rotavirus immunization.
  • Despite a reduction in morbidity attributed to routine rotavirus vaccination, >100,000 children per year are hospitalized in the United States for dehydration from diarrheal illness.


Dehydration is caused by either excessive fluid and salt losses or inadequate intake of fluids.


  • Common sources of fluid loss include
    • GI losses: vomiting, diarrhea (most common cause of dehydration in pediatric patients)
    • Renal losses: diabetes mellitus, diabetes insipidus, diuretics
    • Insensible losses: sweating, fever, tachypnea, increased ambient temperature, large burns
  • Common causes of inadequate fluid intake include
    • Pain from stomatitis, pharyngitis, herpangina, oral trauma
    • Anorexia or malaise
    • Altered mental status
    • Inadequate access to fluids or neglect

There's more to see -- the rest of this topic is available only to subscribers.