Skip to content

Dehydration

Basics

  • Deficiency in total body water.
  • Two types:
  • Water loss
  • Salt and water loss (combination of dehydration and hypovolemia).

Epidemiology

  • Responsible for ~10% of pediatric hospitalizations in the U.S.
  • Stable admission rate ~130 per 100,000 general population in U.S.
  • 37–46% of patients >65 years present with dehydration in European hospitals.
  • 2–3.5% prevalence of dehydration after hospital admission.

Etiology and Pathophysiology

  • Body water lost via skin, lungs, kidneys, GI tract.
  • Negative fluid balance occurs when losses > intake.
  • Types of losses:
  • Insensible: sweat, respiration
  • Obligatory: urine, stool
  • Abdominal: diarrhea, vomiting, osmotic diuresis in diabetic ketoacidosis
  • Hypovolemia can lead to end-organ damage from poor perfusion.
  • Third spacing occurs in effusions, ascites, burns, sepsis.

Geriatric considerations

  • Aging decreases kidney function, urine concentration, thirst, aldosterone, vasopressin, renin.

Risk Factors

  • Children <5 years (highest risk)
  • Elderly
  • Acute/chronic illness
  • Decreased cognition or mental status
  • Lack of access to water
  • High exertion in heat
  • Diuretic use

Clinical Findings

Severity Children (% body weight loss) Adults (% body weight loss) General Condition Radial Pulse Quality Respiration BP Skin Turgor Eyes Tears Mucous Membranes Urine Output Anterior Fontanelle (infants)
Mild 5-10% 3-5% Thirsty, alert, restless Normal Normal Normal Normal Normal Present Moist Normal Normal
Moderate 10-15% 5-10% Lethargic/drowsy Thready/weak Deep Normal to low Reduced, cool Sunken Absent Dry Reduced Sunken
Severe >15% >10% Limp, cold, cyanotic limbs, may be comatose Feeble or impalpable Deep and rapid/tachypnea Low (shock) Skin tenting, cool, mottled, acrocyanotic Very sunken Absent Very dry None passed many hours Markedly sunken

Associated Conditions

  • Hyponatremia
  • Hypernatremia
  • Hypokalemia
  • Hyperglycemia
  • Hypovolemic shock
  • Renal failure
  • Rhabdomyolysis
  • Heat illness

Diagnosis

History

  • Fever
  • Fluid intake (amount, type)
  • Diarrhea (duration, frequency, consistency, mucus/blood)
  • Vomiting (duration, frequency, bilious/nonbilious)
  • Urination pattern
  • Recent illness or contacts
  • Medication history (diuretics, laxatives, steroids)
  • Heat exposure

Physical Exam

  • Vital signs: pulse, BP, temperature
  • Orthostatic vital signs
  • Weight loss percentage
  • Mental status for lethargy
  • Eyes: sunken appearance, tear production
  • Mucous membranes: tacky, dry, parched
  • Capillary refill time (>3 sec)
  • Urine output

Pediatric Considerations

  • Red flags: prolonged capillary refill, abnormal skin turgor, abnormal respiratory pattern.
  • Sunken anterior fontanelle in infants.
  • Monitor number and weight of wet diapers.

Differential Diagnosis

  • Decreased intake: ineffective breastfeeding, anorexia, malabsorption, metabolic disorders, obtunded state
  • Excessive loss: gastroenteritis, febrile illness, diabetic ketoacidosis, hyperglycemia, diabetes insipidus, intestinal obstruction, sepsis

Diagnostic Tests

Initial Tests

  • Mild dehydration: labs often unnecessary.
  • Moderate to severe:
  • Plasma osmolality (gold standard)
  • Urinalysis (specific gravity, hematuria, glucosuria)
  • Serum creatinine, BUN, BUN/creatinine ratio
  • Imaging rarely needed; bedside ultrasound to assess inferior vena cava collapsibility in some adults.

Follow-up Tests

  • Urinalysis less reliable in infants and elderly due to impaired urine concentration.

Treatment

General Measures

  • Oral rehydration therapy (ORT) preferred first-line in mild to moderate dehydration.
  • IV, nasogastric, or intraosseous hydration for moderate to severe cases or if oral intake inadequate.

Medication

  • ORT: small frequent sips (~100 mL every 5 minutes) until symptom stabilization.
  • If ORS unavailable: water, broth, or sports drinks (caution with sports drinks in infectious diarrhea).
  • IV fluids for moderate/severe:
  • Adults: 20 mL/kg/hr crystalloid bolus until stable; then replace deficit and maintenance fluids.
  • Children: 10-20 mL/kg bolus; repeat up to 60 mL/kg; then deficit replacement over 24-48 hrs.
  • Maintenance fluids using 4-2-1 rule for adults and children.
  • Fluid choice:
  • Isotonic saline (0.9% NaCl)
  • Lactated Ringer’s
  • D5 ½ NS + potassium chloride
  • Caution with rapid sodium correction (risk of central pontine myelinolysis).
  • Use smaller boluses and frequent reassessment in elderly, heart failure, kidney disease.
  • NG fluid administration for young children if unable to take orally.

Antiemetics

  • Ondansetron (4-8 mg PO/SL/IV q4-8h) may improve oral hydration success; risk of QT prolongation.
  • Promethazine contraindicated <2 years; risk of respiratory depression; used cautiously.
  • Loperamide may reduce diarrhea duration in children >3 years (not recommended <3 years).

Referral

  • Severe dehydration requiring ICU care.
  • Surgical consult for underlying abdominal issues.

Admission

  • Intractable vomiting/diarrhea
  • Electrolyte abnormalities
  • Hemodynamic instability
  • Inability to tolerate oral rehydration

Inpatient Care

  • Stabilize airway, breathing, circulation.
  • Monitor strict input/output.
  • Use Holliday-Segar method for maintenance fluids in children.

Discharge Criteria

  • Euvolemia restored
  • Oral intake tolerated
  • Underlying cause improving

Ongoing Care

Diet

  • Bland BRAT diet (bananas, rice, applesauce, toast).
  • Small frequent sips of room temperature liquids.
  • Continue breastfeeding; lactose-free feeds if diarrhea present.

Patient Education

  • Seek care if dizziness, lethargy, rapid HR, inability to keep fluids, persistent vomiting or diarrhea, or unusual irritability in infants.

Prognosis

  • Usually self-limited with early treatment.
  • Potentially fatal if untreated.

Complications

  • Seizures
  • Renal failure
  • Cardiovascular arrest

ICD10: - E86.0 Dehydration - E87.1 Hypo-osmolality and hyponatremia - E86.1 Hypovolemia

Clinical Pearls: - Dehydration results from total body water deficit causing negative fluid balance. - Leading cause of hospitalization in adults, children, elderly. - Assess severity, cause, and replacement needs promptly. - Oral rehydration preferred; IV fluids if oral intake inadequate or severe.