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Dehydration Workup

  • Author: Lennox H Huang, MD, FAAP; Chief Editor: Timothy E Corden, MD  more...
 
Updated: Dec 31, 2015
 

Laboratory Studies

No definitive laboratory test for dehydration is available. Laboratory data are generally not required if the etiology is apparent and mild-to-moderate dehydration is present.

With severe dehydration, the following laboratory studies are suggested:

  • Serum sodium should be determined because hyponatremia (< 130 mEq/L) and hypernatremia (>150 mEq/L) require specific treatment regimens.
  • Potassium may be elevated (eg, congenital adrenal hyperplasia, renal failure) or low (eg, pyloric stenosis, alkalosis).
  • Chloride may be low in pyloric stenosis (eg, hypochloremic, hypokalemic, or metabolic alkalosis).
  • Poor tissue perfusion in dehydration results in production of lactic acid. Bicarbonate is consumed as lactic acid levels increase. In diabetic ketoacidosis (DKA), ketoacids also consume bicarbonate. Bicarbonate levels can also be reduced because of loss of bicarbonate in diarrheal stools. Low bicarbonate levels have been correlated with increased severity of dehydration in some studies.
  • Glucose may be dangerously low because of poor intake or extremely elevated in DKA.
  • BUN and creatinine levels may be elevated because of renal hypoperfusion.
  • Urine specific gravity may be elevated in patients with dehydration but should not be relied on because it is not an accurate diagnostic test for dehydration. [11] Further caution should be used in the setting of diabetes insipidus, in which the urine is dilute with low specific gravity, even in patients who are dehydrated.
  • Urinalysis may show findings of DKA (eg, ketones, glucose).
  • Electrolyte analysis of any fluid that is lost (eg, urine, stool, gastric fluid) can be performed to further refine the composition of replacement fluids after providing acute fluid resuscitation.
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Procedures

Intravenous line

If severe dehydration is present, peripheral intravenous line insertion may be difficult. The preferred sites for initial insertion attempts include the basilic and cephalic veins in the antecubital fossa and the saphenous veins near the ankle. Transillumination of the insertion site with a fiberoptic light source may be used to facilitate locating the desired vein.

If peripheral intravenous access cannot be rapidly achieved (< 90 s) in a child with severe dehydration and shock, intraosseous cannulation should be attempted. If the child is not in extremis, more time may be taken to establish central venous access percutaneously (eg, femoral, subclavian, internal, external jugular).

Intraosseous line

Intraosseous cannulation can be easily and rapidly achieved in children younger than 6 years. Specially designed intraosseous infusion needles or Jamshidi-type bone marrow aspiration needles may be used. Short large-bore spinal needles may also be used but often bend during placement. The ideal site of insertion is the anteromedial surface of the tibia, 1-3 cm below the anterior tibial tuberosity. Care must be taken to avoid injury to the physeal growth plate.

Orogastric/nasogastric tube

An orogastric/nasogastric tube may be inserted to facilitate enteral rehydration in children with mild-to-moderate dehydration. These tubes should be considered to assist in the nutritional recovery of children who are critically ill or severely dehydrated.

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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 Association for Physician Leadership, Canadian Medical Association, Ontario Medical Association, Society of Critical Care Medicine

Disclosure: Nothing to disclose.

Coauthor(s)

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, Society of Critical Care Medicine

Disclosure: Nothing to disclose.

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, Ontario Medical Association

Disclosure: Nothing to disclose.

Specialty Editor Board

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, Society of Critical Care Medicine

Disclosure: Nothing to disclose.

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, Wisconsin Medical Society

Disclosure: Nothing to disclose.

Additional Contributors

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/ Holtz Children's Hospital, Jackson Memorial Medical Center; Medical Director, Palliative Care Team, Holtz Children's Hospital; Medical Manager, FEMA, South Florida Urban Search and Rescue, Task Force 2

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, Wilderness Medical Society

Disclosure: Nothing to disclose.

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Table 1. Clinical Findings of Dehydration
Symptom/Sign Mild Dehydration Moderate Dehydration Severe Dehydration
level of consciousness Alert Lethargic Obtunded
Capillary refill* 2 s 2-4 s >4 s, cool limbs
Mucous membranes Normal Dry Parched, cracked
Tears Normal Decreased Absent
Heart rate Slightly increased Increased Very increased
Respiratory rate/pattern* Normal Increased Increased and hyperpnea
Blood pressure Normal Normal, but orthostasis Decreased
Pulse Normal Thready Faint or impalpable
Skin turgor* Normal Slow Tenting
Fontanel Normal Depressed Sunken
Eyes Normal Sunken Very sunken
Urine output Decreased Oliguria Oliguria/anuria
* Best indicators of hydration status[10]
Table 2. Estimated Fluid Deficit
Severity Infants (weight < 10 kg) Children (weight >10 kg)
Mild dehydration 5% or 50 mL/kg 3% or 30 mL/kg
Moderate dehydration 10% or 100 mL/kg 6% or 60 mL/kg
Severe dehydration 15% or 150 mL/kg 9% or 90 mL/kg
Table 3. Composition of Appropriate Oral Rehydration Solutions
Solution Carbohydrate (g/dL) Sodium (mEq/L) Potassium (mEq/L) Base (mEq/L) Osmolality
Pedialyte 2.5 45 20 30 250
Infalyte 3 50 25 30 200
Rehydralyte 2.5 75 20 30 310
WHO/UNICEF* 2 90 20 30 310
* World Health Organization/United Nations Children's Fund
Table 4. Composition of Inappropriate Oral Rehydration Solutions
Solution Carbohydrate (g/dL) Sodium (mEq/L) Potassium (mEq/L) Base (mEq/L) Osmolality
Apple juice 12 0.4 26 0 700
Ginger ale 9 3.5 0.1 3.6 565
Milk 4.9 22 36 30 260
Chicken broth 0 2 3 3 330
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