• Dehydration is a negative balance of body fluid, usually expressed as a percentage of body weight. Mild, moderate, and severe dehydration correspond to deficits of <5%, 5% to 10%, and >10%, respectively.
• Dehydration is classified into three types based on the serum sodium concentration: isotonic (Na <130–150 mmol/L), hypotonic (Na <130 mmol/L), and hypertonic (Na >150 mmol/L).

• Gastrointestinal losses—vomiting, diarrhea (most common cause of dehydration in pediatric patients);
• Renal losses—diabetes mellitus, diabetes insipidus, diuretic agents;
• Insensible losses—sweating, fever, tachypnea, increased ambient temperature, large burns;
• Poor oral intake—stomatitis, pharyngitis, anorexia, oral trauma, altered mental status.

• Severe dehydration may lead to hypovolemic shock and acute renal failure.
• Hyponatremia is associated with hypotonia, hypothermia, and seizures.
• Overly rapid correction of hypernatremia can produce cerebral edema.

Question: Frequency and duration of emesis and/or diarrhea?
Significance: This will give a rough estimate of risk of dehydration.

Question: Amount and type of liquids taken?
Significance: If there were large quantities of water, be alert for hyptonic dehydration. If excessive electrolyte solution used for hydration, may have hypertonic dehydration.

Question: Frequency and quantity of urination (may be difficult to estimate in infants with diarrhea)?
Significance: Decreased urination indicates possibility of dehydration.

Question: Fever?
Significance: Fever increases insensible water loss.

Question: Exertion or heat exposure?
Significance: Increases insensible water loss.

Finding: General appearance
Significance: Lethargy, irritability, thirst

Finding: Vital signs
Significance: Tachycardia; orthostatic increase in heart rate or hypotension; hyperpnea

Finding: Skin
Significance: Prolonged capillary refill at fingertip (<2 seconds is normal in warm environment); mottling; poor turgor

Finding: Eyes
Significance: Decreased or absent tears; sunken eyes

Finding: Mucous membranes
Significance: Dry or parched

Finding: Anterior fontanelle
Significance: Sunken

• Physical signs generally appear when the deficit is at least 2% to 3%.
• No single finding is pathognomonic of dehydration. A reasonable guideline is that the presence of three or more findings indicates at least mild dehydration. The number and severity of physical signs increase with the degree of dehydration.
• Urine output decreases early in the course of dehydration, and a history of decreased urination is a non-specific finding.
• Capillary refill time is a specific indicator, but may be falsely prolonged by cool ambient temperature (<20°C or <68°F). It is not affected by fever.
• Children with a deficit greater than 15% will show signs of cardiovascular instability such as severe tachycardia and hypotension.
• Physical findings are more significant for a given degree of dehydration in children with hyponatremia, leading to overestimation of the deficit. Conversely, the clinical picture is somewhat moderated in hypernatremia.

Test: Serum sodium
Significance: Classifies type of dehydration. Hyponatremia and hypernatremia are uncommon (<5% of cases). Measure sodium levels in cases of clinically severe disease, or if risk factors are present (e.g., young infant, history of excessive free water intake).

Test: Rapid glucose test or serum glucose
Significance: To detect hypoglycemia due to prolonged fasting

Test: Urine specific gravity
Significance: This is elevated early in dehydration, but may not become elevated at all in young infants or children with sickle cell disease.

Test: Serum bicarbonate
Significance: This is frequently low with diarrheal illness, even in the absence of dehydration. Useful to detect significant acidosis when dehydration is clinically severe.

Test: Blood urea nitrogen (BUN)
Significance: Rises only late in dehydration in children.

• Use rehydration solution containing 2% to 2.5% glucose and 75 to 90 mmol/L Na (e.g., WHO solution), or 45 to 50 mmol/L Na (e.g., Pedialyte [Ross Laboratories, Columbus OH], Infalyte, [Mead Johnson, Evansville, IN]).
• Replace entire deficit in 4 to 6 hours—for mild dehydration, 50 mL/kg; for moderate to severe dehydration, 80 to 100 mL/kg. Include ongoing losses, approximately 5 mL/kg for each diarrheal stool.
• Begin with slow administration, with strict limits when vomiting is present—5 mL every 1 to 2 minutes. For infants, use a syringe or spoon rather than a bottle. After 1 hour, if the oral liquids have been tolerated, increase the volume and rate.
• Have the child’s caregiver participate in giving the fluids, and provide education regarding fluid replacement and signs of dehydration.
• Monitor weight, intake and output, and clinical signs. Failure of ORT includes intractable vomiting, clinical deterioration, or lack of improvement after 4 hours.

• Administer intravenous bolus of normal saline or Ringer lactate, 20 mL/kg, over 10 to 30 minutes. Repeat as needed to restore cardiovascular stability. Avoid dextrose-containing solutions for boluses except to correct documented hypoglycemia.
• Calculate maintenance fluid requirements: 100 mL/kg for the first 10 kg, plus 50 mL/kg for the next 10 kg, plus 20 mL/kg over 20 kg.
• Calculate fluid deficit based on clinical estimate or known weight loss. For isotonic or hypotonic dehydration, give one-third to one-half normal saline with 5% dextrose, at a rate to provide maintenance and replace deficit over 24 hours. For hypertonic dehydration, replace deficit over 48 hours, using one-fifth to one-fourth normal saline with 5% dextrose.
• Monitor weight, intake and output, and clinical signs. With hypernatremia, measure serum sodium every 4 to 6 hours; do not exceed rate of fall of 1 mmol/L/h.

After rehydration, children with ongoing losses, as in gastroenteritis, should receive a maintenance solution in addition to regular feedings to maintain a positive fluid balance. Recommend 5 to 10 mL/kg for each diarrheal stool. Avoid clear liquids with excessive glucose, such as fruit juices, punches, and soft drinks, as these can promote osmotic fluid losses in the stool. In infants less than 6 months old, do not give large amounts of plain water, which can lead to hyponatremia.

Q: How can an oral rehydration solution be prepared at home?
A: An acceptable rehydration solution (2.2% glucose, 70 mmol Na/L) can be prepared with the following: ½ teaspoon of table salt, ½ teaspoon of baking soda, and 1 cup of orange juice, added to 3 cups of water. For maintenance solution, decrease the table salt to ¼ teaspoon.

Q: Can commercially available maintenance solutions be used for rehydration as well as maintenance?
A: Data suggest that reduced-osmolarity maintenance solutions, with a sodium concentration of 45 to 50 mmol/L, are equally effective for rehydration as solutions with a higher sodium content.

Q: How can oral rehydration solution be made more palatable?
A: Rehydration solutions may be more palatable if iced, or flavored with apple or orange juice (1 part juice to 4 parts rehydration solution) or unsweetened Kool-Aid powder (2.5 mL powder per 240 mL of solution).

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