eMedicine Specialties > Pediatrics: Cardiac Disease and Critical Care Medicine > Critical Care
Dehydration
Updated: Jul 21, 2008
Introduction
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.
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.
- 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.
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.
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.
Clinical
History
- Intake of fluids, including the volume, type (hypertonic or hypotonic), and frequency
- Urine output, including the frequency of voiding (last wet diaper), presence of concentrated or dilute urine, hematuria
- Stool output, frequency of stools, stool consistency, presence of blood or mucus in stools
- Emesis, including frequency and volume and whether bilious or nonbilious, hematemesis
- Contact with ill people, especially others with gastroenteritis, use of daycare
- Underlying illnesses, especially cystic fibrosis, diabetes mellitus, hyperthyroidism, renal disease
- Fever
- Appetite patterns
- Weight loss
- Travel
- Recent antibiotic use
- Possible ingestions
Physical
A complete physical examination may assist in determining the underlying cause of the patient's dehydration and in defining the severity of dehydration. The clinical assessment of severity of dehydration determines the approach to management. In general, physical signs of dehydration have poor precision and accuracy. Rather than attempting to assign an exact percentage of dehydration, one should attempt to place the child in one of 3 broad categories.
Determination dehydration severity should be based on the overall constellation of symptoms. Patients in a given category need not exhibit all the signs and symptoms listed below. Literature reviews have suggested that delayed capillary refill, delayed skin turgor, and abnormal respiratory pattern are the most reliable clinical signs of dehydration in children.
Table 1. Clinical Findings of Dehydration
Open table in new window
Table
| Symptom/Sign | Mild Dehydration | Moderate Dehydration | Severe Dehydration |
|---|---|---|---|
| Level of consciousness | Alert | Lethargic | Obtunded |
| Capillary refill* | 2 Seconds | 2-4 Seconds | Greater than 4 seconds, 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 |
| Symptom/Sign | Mild Dehydration | Moderate Dehydration | Severe Dehydration |
|---|---|---|---|
| Level of consciousness | Alert | Lethargic | Obtunded |
| Capillary refill* | 2 Seconds | 2-4 Seconds | Greater than 4 seconds, 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 status1
Table 2. Estimated Fluid DeficitOpen table in new window
Table
| 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 |
| 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 |
Causes
Determination of the cause of dehydration is essential. Poor fluid intake, excessive fluid output, increased insensible fluid losses, or a combination of the above may cause intravascular volume depletion. Successful treatment requires identification of the underlying disease state.
- Common causes
- Gastroenteritis: This is the most common cause of dehydration. If both vomiting and diarrhea are present, dehydration may rapidly progress.
- Stomatitis: Pain may severely limit oral intake.
- Diabetic ketoacidosis (DKA): Dehydration is caused by osmotic diuresis. Weight loss is caused by both excessive fluid losses and tissue catabolism. Rapid rehydration, especially rapid initial volume resuscitation, may be associated with a poor neurologic outcome. DKA requires very specific and controlled treatment (see Diabetic Ketoacidosis).
- Febrile illness: Fever causes increased insensible fluid losses and may affect appetite.
- Pharyngitis: This may decrease oral intake.
- Life-threatening causes
- Gastroenteritis
- DKA
- Burns: Fluid losses may be extreme. Very aggressive fluid management is required (see Burns, Thermal).
- Congenital adrenal hyperplasia: This may have associated hypoglycemia, hypotension, hyperkalemia, and hyponatremia.
- GI obstruction: This is often associated with poor intake and emesis. Bowel ischemia can result in extensive capillary leak and shock.
- Heat stroke: Hyperpyrexia, dry skin, and mental status changes may occur.
- Cystic fibrosis: This results in excessive sodium and chloride losses in sweat, placing patients at risk for severe hyponatremic hypochloremic dehydration.
- Diabetes insipidus: Excessive output of very dilute urine can result in large free water losses and severe hypernatremic dehydration.
- Thyrotoxicosis: Weight loss is observed, despite increased appetite. Diarrhea occurs.
More on Dehydration |
 Overview: Dehydration |
| Differential Diagnoses & Workup: Dehydration |
| Treatment & Medication: Dehydration |
| Follow-up: Dehydration |
| References |
| Next Page » |
References
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Further Reading
Keywords
dehydration, negative fluid balance, diarrheal illness, diarrhea, isonatremic dehydration, hypernatremic dehydration, hyponatremic dehydration, end organ failure, cerebral edema, gastroenteritis, cystic fibrosis, diabetes mellitus, hyperthyroidism, gastroenteritis, stomatitis, diabetic ketoacidosis, DKA, pharyngitis, burns, congenital adrenal hyperplasia, hypotension, hyperkalemia, GI obstruction, hyperkalemia, hypoglycemia, hypotension, bowel ischemia, diabetes insipidus, pyloric stenosis, alkalosis
