Dehydration 

  • Author: Lennox H Huang, MD, FAAP; Chief Editor: Timothy E Corden, MD   more...
 
Updated: Mar 12, 2012
 

Background

Dehydration describes a state of negative fluid balance that may be caused by numerous disease entities. Diarrheal illnesses are the most common etiologies. Worldwide, dehydration secondary to diarrheal illness is the leading cause of infant and child mortality.

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Pathophysiology

The negative fluid balance that causes dehydration results from decreased intake, increased output (renal, GI, or insensible losses), or fluid shift (ascites, effusions, and capillary leak states such as burns and sepsis). The decrease in total body water causes reductions in both the intracellular and extracellular fluid volumes. Clinical manifestations of dehydration are most closely related to intravascular volume depletion. As dehydration progresses, hypovolemic shock ultimately ensues, resulting in end organ failure and death.

Young children are more susceptible to dehydration due to larger body water content, renal immaturity, and inability to meet their own needs independently. Older children show signs of dehydration sooner than infants due to lower levels of extracellular fluid (ECF).

Dehydration can be categorized according to osmolarity and severity. Serum sodium is a good surrogate marker of osmolarity assuming the patient has a normal serum glucose. Dehydration may be isonatremic (130-150 mEq/L), hyponatremic (< 130 mEq/L), or hypernatremic (>150 mEq/L). Isonatremic dehydration is the most common (80%). Hypernatremic and hyponatremic dehydration each comprise 5-10% of cases. Variations in serum sodium reflect the composition of the fluids lost and have different pathophysiologic effects.

  • Isonatremic (isotonic) dehydration occurs when the lost fluid is similar in sodium concentration to the blood. Sodium and water losses are of the same relative magnitude in both the intravascular and extravascular fluid compartments.
  • Hyponatremic (hypotonic) dehydration occurs when the lost fluid contains more sodium than the blood (loss of hypertonic fluid). Relatively more sodium than water is lost. Because the serum sodium is low, intravascular water shifts to the extravascular space, exaggerating intravascular volume depletion for a given amount of total body water loss.[1, 2]
  • Hypernatremic (hypertonic) dehydration occurs when the lost fluid contains less sodium than the blood (loss of hypotonic fluid). Relatively less sodium than water is lost. Because the serum sodium is high, extravascular water shifts to the intravascular space, minimizing intravascular volume depletion for a given amount of total body water loss.[3, 4, 2]

Neurologic complications can occur in hyponatremic and hypernatremic states. Severe hyponatremia may lead to intractable seizures, whereas rapid correction of chronic hyponatremia (>2 mEq/L/h) has been associated with central pontine myelinolysis. During hypernatremic dehydration, water is osmotically pulled from cells into the extracellular space. To compensate, cells can generate osmotically active particles (idiogenic osmoles) that pull water back into the cell and maintain cellular fluid volume. During rapid rehydration of hypernatremia, the increased osmotic activity of these cells can result in a large influx of water, causing cellular swelling and rupture; cerebral edema is the most devastating consequence. Slow rehydration over 48 hours generally minimizes this risk.

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Epidemiology

Frequency

United States

Diarrheal illnesses in children causes 3 million physician visits, 220,000 hospitalizations (10% of all children who require hospitalization), and 400 deaths per year. On average, North American children younger than 5 years have 2 episodes of gastroenteritis per year.

International

Diarrheal illnesses with subsequent dehydration account for nearly 4 million deaths per year in infants and children. The overwhelming majority of these deaths occur in developing nations.

Mortality/Morbidity

Mortality and morbidity generally depend on the severity of dehydration and the promptness of oral or intravenous rehydration. If treatment is rapidly and appropriately obtained, morbidity and mortality are low.

Routine use of hypotonic parenteral fluids in hospitalized children has been associated with hyponatremia and subsequent neurologic complications and death. Monitoring the efficacy and complications of parenteral rehydration with accurate fluid balances and serum electrolytes is crucial.

Age

Children younger than 5 years are at the highest risk.

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Contributor Information and Disclosures
Author

Lennox H Huang, MD, FAAP  Associate Professor and Chair, Department of Pediatrics, McMaster University School of Medicine; Chief of Pediatrics, McMaster Children's Hospital

Lennox H Huang, MD, FAAP is a member of the following medical societies: American Academy of Pediatrics, American College of Physician Executives, Canadian Medical Association, Ontario Medical Association, and Society of Critical Care Medicine

Disclosure: Nothing to disclose.

Coauthor(s)

Krishnapriya R Anchala, MD, MS, FAAP  Assistant Professor, Department of Pediatrics, Division of Pediatric Emergency Medicine, McMaster University

Krishnapriya R Anchala, MD, MS, FAAP is a member of the following medical societies: American Academy of Pediatrics, Canadian Medical Association, and Ontario Medical Association

Disclosure: Nothing to disclose.

Dan L Ellsbury, MD  Consulting Staff, Pediatrix Medical Group of Iowa; Consulting Staff, Department of Pediatrics, Neonatology Intensive Care Unit, Mercy Medical Center of Des Moines

Dan L Ellsbury, MD is a member of the following medical societies: American Academy of Pediatrics

Disclosure: Nothing to disclose.

Caroline S George, MD  Associate Professor, Consulting Staff, Department of Pediatrics, Division of Critical Care Medicine, University of Minnesota Medical School

Caroline S George, MD is a member of the following medical societies: American Academy of Pediatrics and Society of Critical Care Medicine

Disclosure: Nothing to disclose.

Specialty Editor Board

G Patricia Cantwell, MD, FCCM  Professor of Clinical Pediatrics, Chief, Division of Pediatric Critical Care Medicine, University of Miami, Leonard M Miller School of Medicine; Medical Director, Palliative Care Team, Director, Pediatric Critical Care Transport, Holtz Children's Hospital, Jackson Memorial Medical Center; Medical Manager, FEMA, Urban Search and Rescue, South Florida, Task Force 2; Pediatric Medical Director, Tilli Kids – Pediatric Initiative, Division of Hospice Care Southeast Florida, Inc

G Patricia Cantwell, MD, FCCM is a member of the following medical societies: American Academy of Hospice and Palliative Medicine, American Academy of Pediatrics, American Heart Association, American Trauma Society, National Association of EMS Physicians, Society of Critical Care Medicine, and Wilderness Medical Society

Disclosure: Nothing to disclose.

Mary L Windle, PharmD  Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Nothing to disclose.

Barry J Evans, MD  Assistant Professor of Pediatrics, Temple University Medical School; Director of Pediatric Critical Care and Pulmonology, Associate Chair for Pediatric Education, Temple University Children's Medical Center

Barry J Evans, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Chest Physicians, American Thoracic Society, and Society of Critical Care Medicine

Disclosure: Nothing to disclose.

Mary E Cataletto, MD  Director of Children's Sleep Services, Winthrop Sleep Disorders Center, Mineola, NY; Professor of Clinical Pediatrics, State University of New York at Stony Brook, Stony Brook, NY

Mary E Cataletto, MD is a member of the following medical societies: American Academy of Pediatrics and American College of Chest Physicians

Disclosure: Shering Plough Pharmaceuticals Honoraria Consulting

Chief Editor

Timothy E Corden, MD  Associate Professor of Pediatrics, Co-Director, Policy Core, Injury Research Center, Medical College of Wisconsin; Associate Director, PICU, Children's Hospital of Wisconsin

Timothy E Corden, MD is a member of the following medical societies: American Academy of Pediatrics, Phi Beta Kappa, Society of Critical Care Medicine, and Wisconsin Medical Society

Disclosure: Nothing to disclose.

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Table 1. Clinical Findings of Dehydration
Symptom/SignMild DehydrationModerate DehydrationSevere Dehydration
level of consciousnessAlertLethargicObtunded
Capillary refill*2 s2-4 s>4 s, cool limbs
Mucous membranesNormalDryParched, cracked
TearsNormalDecreasedAbsent
Heart rateSlightly increasedIncreasedVery increased
Respiratory rate/pattern*NormalIncreasedIncreased and hyperpnea
Blood pressureNormalNormal, but orthostasisDecreased
PulseNormalThreadyFaint or impalpable
Skin turgor*NormalSlowTenting
FontanelNormalDepressedSunken
EyesNormalSunkenVery sunken
Urine outputDecreasedOliguriaOliguria/anuria
* Best indicators of hydration status[6]
Table 2. Estimated Fluid Deficit
SeverityInfants (weight < 10 kg)Children (weight >10 kg)
Mild dehydration5% or 50 mL/kg3% or 30 mL/kg
Moderate dehydration10% or 100 mL/kg6% or 60 mL/kg
Severe dehydration15% or 150 mL/kg9% or 90 mL/kg
Table 3. Composition of Appropriate Oral Rehydration Solutions
SolutionCarbohydrate (g/dL)Sodium (mEq/L)Potassium (mEq/L)Base (mEq/L)Osmolality
Pedialyte2.5452030250
Infalyte3502530200
Rehydralyte2.5752030310
WHO/UNICEF*2902030310
* World Health Organization/United Nations Children's Fund
Table 4. Composition of Inappropriate Oral Rehydration Solutions
SolutionCarbohydrate (g/dL)Sodium (mEq/L)Potassium (mEq/L)Base (mEq/L)Osmolality
Apple juice120.4260700
Ginger ale93.50.13.6565
Milk4.9223630260
Chicken broth0233330
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