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Article
fluid & electrolytes
Dehydration in Infancy and
Childhood
Laurence Finberg, MD*
Objectives
1.
2.
3.
4.
After completing this article, readers should be able to:
List the conditions under which dehydration can occur.
Describe the first step in therapy of dehydration.
Explain how to treat isonatremic and hypernatremic dehydration.
Delineate when oral hydration may be started and why.
Definition
The concept of dehydration did not enter clinical medicine until the 1830s and was not
scientifically defined for some years after that. Although the word dehydration in general
English usage means loss of water, in physiology and medicine, the unmodified word
means a loss of water and salt or extracellular fluid (ECF), the most common of the
clinically recognized types of dehydration. Depending on the type of pathophysiologic
process, water and salts (primarily sodium chloride) may be lost in physiologic proportion
or lost disparately, with each type producing a somewhat different clinical picture. We have
found it useful to designate these types as isonatremic (classical), hypernatremic (hypertonic), or hyponatremic (hypotonic). The differential losses produce different clinical
features because of the functional impermeability of the Na⫹ and Cl- ions of the ECF to
the adjacent intracellular fluid (ICF). We use sodium rather than chloride in the nomenclature because chloride ions are simultaneously involved in a reciprocal relationship with
bicarbonate ions. Such classification of the clinical entities has proved useful for understanding of the pathogenesis and especially for treatment.
Etiology and Epidemiology
Dehydration is a physiologic disturbance that occurs in a wide variety of circumstances
affecting water and salt losses. The most common associated disease group among infants
is the infectious diarrheas caused by viral and bacterial agents. The most frequent
pathogens in the United States are the several rotavirus species, which are most prevalent
in the winter months. Bacterial diarrhea, currently seen less commonly over the past 40
years, occurs more often in the summer months, as do some types of disease due to viral
causes other than rotavirus. When malnutrition is present, diarrhea resulting in dehydration is a leading cause of death in parts of the world where poverty and poor hygiene are
commonplace. These circumstances have become uncommon, although not unknown in
the United States. Other causes of dehydration include diabetic ketoacidosis (DKA),
diabetes insipidus, the stress of surgery, and simple water deprivation.
Pathophysiology and Pathogenesis
Understanding the disturbances of dehydration requires knowledge about body composition and the continuing requirements for water and electrolytes.
Composition
The lean body mass (LBM) of humans is 70% water, with 25% of the LBM in infants in the
ECF and 45% in the ICF (Figs 1 and 2). Within the ECF is the plasma (about 6% of the
LBM at all ages), which is contained within its compartment by the small osmotic (oncotic)
concentration (1 to 2 mOsm/kg) of protein molecules that limits their permeability
*Clinical Professor of Pediatrics, University of California at San Francisco and Stanford University School of Medicine, San
Francisco, CA.
Pediatrics in Review Vol.23 No.8 August 2002 277
fluid & electrolytes dehydration
Requirements
To maintain a constant body temperature,
humans produce heat and lose it at a controlled rate, in part by evaporation of water
from the skin (30 mL/100 kcal expended)
and from the lungs (15 mL/100 kcal expended), which is termed insensible water
loss. Both of these amounts increase during
hyperthermia, hyperventilation, and continuous muscle contractions. The losses may
increase threefold if all three conditions occur simultaneously. Hyperthermia alone will
double insensible losses, as will a very warm
environment.
When dehydration occurs because of diarrhea, homeostatic mechanisms usually adjust so that water and sodium chloride are
lost in physiologic proportion, thus maintaining the sodium concentration in serum
within the normal range. When vomiting
also occurs, water intake is curtailed, making
water loss proportionally greater than salt
losses and resulting in hypernatremia. When
massive stool loss of water and salt is ongoing
and the only intake is water, salt losses predominate, resulting in a hyponatremic state.
When dehydration occurs, several other
disturbances come into play. The process of
circulatory depletion from plasma loss and
concomitant starvation lead to excess hydrogen ion accumulation and reduced urine
output. Stool losses also contain intracellular
ions, particularly potassium, and uncomFigure 1. Composition of lean body mass (fat-free) of the infant. Reprinted monly, calcium homeostasis may be altered.
with permission from Finberg L, Kravath RE, Hellerstein S. Water and ElectroThese combined disturbances may be
lytes in Pediatrics. 2nd ed. Philadelphia, Pa: WB Saunders; 1993.
summed up in five categories: volume, osmolality (body space alterations), acid-base
markedly. The ECF and ICF compartments are mainor hydrogen ion, potassium losses, and calcium disturtained separately despite free permeability of water and
bance.
Na⫹ and Cl- ions via the energy-dependent extrusion of
sodium from cells and the obligate phosphate and negaClinical Aspects
tively charged protein within cells. From 12 to 18
The first objective sign of dehydration is an increase in
months to about 5 years of age, the proportions gradupulse rate as a response to reduced plasma volume;
ally evolve into 20% ECF and 50% ICF. Thus, the comsubjectively, there may be increased thirst. When a hypositional maturity for body water components is compernatremic state is produced, tachycardia is less proplete at approximately 5 years of age. For the first 6 to 12
nounced because ECF (hence plasma) is relatively promonths after birth and for all malnourished patients, the
tected, although fever may offset this difference. Thirst
LBM and weight may be considered identical, with water
may be intense. Changes in acute diarrhea usually are not
content comprising 70% of weight. In older and optinoted until approximately 5% of the body weight (7% of
mally nourished children, about 10% of body weight is
LBM) has been lost. If the process continues untreated,
fat, making body water content 60% of total weight.
circulatory insufficiency predominates clinically. The
278 Pediatrics in Review Vol.23 No.8 August 2002
fluid & electrolytes dehydration
Hypernatremic states are characterized
by attenuated signs of circulatory deficiency because plasma volume is better preserved per degree of dehydration, but neurologic abnormalities appear. There may be
a combination of lethargy, hyperresponsivness to stimuli, velvety feel to skin, a
“doughy” feel to the subcutaneous tissue,
increased deep tendon reflexes, and as the
condition worsens, coma and convulsions.
At the most extreme, plasma volume also
may be compromised, producing a nearmoribund state that requires immediate resuscitation by restoration of the plasma volume.
The hyponatremically dehydrated patient presents as an exaggeration of the
isonatremically dehydrated state.
Laboratory Analysis
Very mildly dehydrated patients may be
managed without laboratory determinations, but it is wise to confirm clinical impressions in moderate losses and always in
Figure 2. Ionic profiles of body fluids: approximate representation of cations and
severe illness. Sodium, chloride, bicarbonanions of the three principal body fluid compartments. All are electrically neutral
ate, and urea nitrogen determinations are
and all have the same osmolality despite differences in total charges. The shaded
the most essential. An arterial blood gas
areas represent large molecules or bound ions whose osmolal contribution
(mOsm/kg) is quantitatively much less than their electric charge (mEq/kg), but may be helpful and may be obtained
which are of great importance to the distribution of ions because of their quickly in more severely ill patients. Potasimpermeability. Reprinted with permission from Finberg L, Kravath RE, Hellerstein sium and calcium levels are occasionally
S. Water and Electrolytes in Pediatrics. 2nd ed. Philadelphia, Pa: WB Saunders; helpful. The urea nitrogen level gives a
1993.
rough estimate of renal compromise. It is
the reduced renal function that produces
most useful clinical sign is the capillary refill time (turthe acidemia rather than the loss of base in the stool for
gor): normal is less than 2 seconds, 2 to 2.9 seconds
which compensation readily occurs.
corresponds to 50 to 90 mL/kg loss, 3.0 to 3.5 seconds
corresponds to 90 to 110 mL/kg, 3.5 to 3.9 seconds
Management
corresponds to 110 to 120 mL/kg, and more than
Treatment is based on the severity of dehydration and the
4 seconds corresponds to 150 mL/kg. Although not
diagnosis of the differential losses of ECF and ICF (ie,
perfectly predictive, this is the only quantitatively useful
isonatremic, hypernatremic, or hyponatremic).
sign. Even if the patient is febrile, the estimates are
Severity and type of loss may be assessed best with a
reliable if room temperature is not excessively hot.
five-point diagnostic analysis:
Other clinical signs of dehydration include mottled
1. Volume: That which has been and that which will
cool extremities, sunken fontanelle in infants, dry mucontinue to be lost. The first assessment is the deficit,
cous membranes, receded eyeballs, hyperpnea, and loss
which may be determined roughly from the rate of
of skin elasticity in infants (the degree of loss does not
capillary refill corresponding to ECF loss, as noted precorrelate with degree of volume loss). The sensorium
viously. Estimating the volume begins by adding the
usually remains intact until dehydration becomes modobligatory daily replacement for each day of therapy. The
erate (⬎6% of weight). A weak cry and stupor suggest a
Table shows the basal calorie expenditure at various ages
shock state (capillary refill ⬎4 sec). Hypotension is a late
that determines the obligatory maintenance requiremanifestation of dehydration.
ment. The usual patient expends about l.5 times the basal
Pediatrics in Review Vol.23 No.8 August 2002 279
fluid & electrolytes dehydration
Basal Caloric Expenditure for
Infants and Children
Table.
Age
Weight
(kg)
Surface
Area (M2)
Caloric
Expenditure
(kcal/kg)
Newborn
1 wk to 6 mo
6 to 12 mo
1 to 2 y
2 to 5 y
5 to 10 y
10 to 16 y
Adult
2.5 to 4
3 to 8
8 to 12
10 to 15
15 to 20
20 to 35
35 to 60
70
0.2 to 0.23
0.2 to 0.35
0.35 to 0.45
0.45 to 0.55
0.6 to 0.7
0.7 to 1.1
1.5 to 1.7
1.75
50
65
50
45
45
40
25
15
to 70
to 60
to 50
to 45
to 40
to 20
Reprinted with permission from Finberg L, Kravath RE, Hellerstein S.
Water and Electrolytes in Pediatrics. 2nd ed. Philadelphia, Pa: 1993.
rate. High fever may increase this to twice the basal rate,
and high fever plus hyperventilation and excessive muscle
movement as in a convulsion may increase the requirement to three times the basal expenditure.
2. Osmolality: Circulatory deficits represent ECF,
including plasma loss. Neurologic signs and a history of
early abrupt cessation of water intake suggest hypernatremia within an estimated loss of 100 mL/kg. This can be
confirmed or refuted by analysis of the sodium concentration. In the presence of DKA, this is determined by
sodium plus glucose (mmol/L) or by osmolality
(mOsm/kg) of water. DKA is a hyperosmolal state and,
thus, physiologically similar to hypernatremic states.
3. Hydrogen ion (acid-base equilibrium): Failing
renal perfusion brings about acidosis or acidemia in
diarrheal disease. Ketosis creates acidemia in DKA. Alkalotic dehydration occurs when there is high obstructive
vomiting (eg, pyloric stenosis) or excessive bicarbonate
ingestion or infusion plus dehydration. It is appropriate,
therefore, to administer physiologic amounts of bicarbonate in the acidotic patient (ie, four chloride ions for
each bicarbonate) and to use only chloride in the uncommon alkalotic patient. If the bicarbonate is omitted, the
infant or child generally can compensate, but if there has
been renal or pulmonary damage, a balanced solution
may be important. Balanced (eg, sodium chloridebicarbonate) solution should be used routinely, except as
noted previously. Lactate or acetate may be used as a
substitute base for bicarbonate.
4. ICF ions: Potassium loss via the stool in diarrhea
and via the urine in DKA must be replaced. This step is
postponed until circulation is restored and urine production is determined.
280 Pediatrics in Review Vol.23 No.8 August 2002
5. Skeletal exchanges: Changes are uncommon.
Among young infants, calcium ion concentration may be
reduced because of phosphate retention. In hypernatremic states at any age, but especially in infants, ionized
calcium concentration may decrease, although usually
not to a clinically significant degree.
Implementation of Analysis
Serious Isonatremic or Hyponatremic
Dehydration
Treatment for losses of 100 mL/kg or greater consists of
three phases for the patient in or near shock and requires
an initial intravenous route of administration.
EMERGENCY. This phase involves the quick restoration of plasma volume. Several options are available.
1. 5% albumin (20 mL/kg), quickly followed by 10%
glucose in water (20 mL/kg) in 30 minutes.
2. Balanced isotonic sodium salt solution or 0.9%
sodium chloride (40 mL/kg) over 30 to 60 minutes.
3. Balanced isotonic sodium salt solution (20 mL/kg)
over 20 minutes, followed by 10% glucose solution
(20 mL/kg) over 20 minutes. This regimen restores
urine formation faster than does the previous one.
REPLETION. This phase works to restore the ECF following the administration of 20 to 40 mL/kg of fluid.
The aim is to restore the deficit in 24 hours while
meeting the usual obligatory losses and any ongoing
abnormal losses. For the infant whose estimated deficit is
100 mL/kg and maintenance requirement of 1.5⫻basal
is another 100 mL/kg, 160 mL/kg remains to be delivered. Because 50% of this is for deficit and 50% for maintenance, the sodium concentration in delivered fluid should
be 150/2⫽75 mEq/L (75 mmol/L) (range, 60 to
80 mEq/L [60 to 80 mmol/L]), chloride should be 50 to
55 mEq/L (50 to 55 mmol/L), and bicarbonate or lactate
should be 20 to 25 mEq/L (20 to 25 mmol/L) in a 5%
glucose solution to provide calories. The combined emergency and repletion phases should last about 8 hours,
during which 50% of the day’s calculated total should be
delivered. When urine production has been assured, potassium chloride or potassium acetate may be added to the
infusion at 20 mEq/L (20 mmol/L). If acetate is used, the
bicarbonate is reduced or eliminated.
EARLY RECOVERY. ICF restoration is the focus of this
phase. For the next 16 hours, the same solution may be
continued at a slower rate to infuse the full 200 mL/kg
(in this example). Any ongoing abnormal losses should
be replaced by additional fluid of similar composition.
fluid & electrolytes dehydration
Hypernatremic Dehydration
The principle in this condition is to extend the recovery
period over 48 hours so as not to cause cerebral swelling
with too rapid administration of the low-sodium concentration fluid.
VOLUME. Estimated deficit plus 2 days of usual requirements are administered. For an infant, this would be
300 mL/kg.
OSMOLALITY. The deficit of sodium may be replaced
by a 100-mL/kg solution containing 80 to 100 mEq/L
(80 to 100 mmol/L) of sodium. Maintenance for
48 hours would be 200 mL/kg for an infant, which
results in 25 to 33 mEq/L (25 to 33 mmol/L) sodium in
(preferably) 2% to 3% glucose. The lower concentration
of glucose is preferred although not essential because
hyperglycemia may appear in hypernatremic states.
HYDROGEN ION. The anions should be a mixture of
chloride and lactate. No bicarbonate is included if calcium is to be added, thereby avoiding precipitation.
ICF IONS. A maximum safe concentration of potassium is infused to replace cellular losses and to keep the
infused solution at an optimal concentration to avoid
brain swelling.
SKELETAL IONS. A 10-mL ampule of 10% calcium
gluconate per 500 mL of infusion is recommended to
combat occasional hypocalcemia.
Oral intake of a glucose-electrolyte mixture may be
initiated when tolerated and feeding resumed soon afterward.
Moderate Dehydration
For a 50- to 90-mL/kg deficit, there are two options:
1. Isotonic sodium solution administered intravenously in repeated 20-mL/kg increments until circula-
tion is restored is followed by an oral glucose-electrolyte
mixture for the remainder of the deficit and maintenance.
The oral solution should contain 45 to 60 mEq/L (45 to
60 mmol/L) of sodium and continued until a 24-hour
volume (150 to 200 mL/kg) has been attained. Normal
feeding then usually may be resumed. Use of this simple
method should not preclude careful assessment of the
nature and severity of the physiologic disturbance.
2. Complete oral rehydration with an initial solution
of sodium concentration of 75 to 90 mEq/L (75 to
90 mmol/L) (eg, the World Health Organization solution of 90 mEq/L [90 mmol/L] of sodium or a commercially available solution of 75 mEq/L [75 mmol/L]
of sodium) that provides 40 to 50 mL/kg over the first
1 to 4 hours. Even in the presence of vomiting, slow
administration with spoon or dropper (infants) allows
success in 90% to 95% of patients. This phase of therapy
should be under the direct supervision of a physician or
nurse. When circulation has returned, as indicated by a
normal pulse rate, the oral mixture is changed to a
maintenance one of 40 to 50 mEq/L (40 to
50 mmol/L) of sodium and 20 mEq/L (20 mmol/L) of
potassium. For either moderate or mild dehydration that
is hyponatremic, the proportion of isotonic sodium solution is increased, keeping the volume the same as
calculated for isonatremic states.
Mild Dehydration
The oral maintenance solution for a 50-mL/kg deficit or
less can be administered for approximately 12 hours at
the rate of 150 mL/kg per day. Usual feedings can be
restarted when appropriate.
Suggested Reading
Finberg L, Kravath RE, Hellerstein S. Water and Electrolytes in
Pediatrics. 2nd ed. Philadelphia, Pa: WB Saunders; 1993
Holliday M. The evolution of therapy for dehydration: should
deficit therapy still be taught? Pediatrics. 1996;98:171–177
Pediatrics in Review Vol.23 No.8 August 2002 281
fluid & electrolytes dehydration
PIR Quiz
Quiz also available online at www.pedsinreview.org.
6. A 6-week-old boy presents with vomiting for the past 2 weeks. Vomiting is described as forceful. It occurs
5 to 10 minutes after feeding and consists primarily of milk. Physical examination reveals: heart rate,
140 beats/min; respirations, 20 breaths/min; temperature, 98.2°F (36.8°C); and blood pressure, 90/50 mm
Hg. The anterior fontanelle is depressed. The infant is alert, responds appropriately to stimuli, and sucks
vigorously on a milk bottle. Skin turgor is diminished, with a capillary refill time of 2 to 3 seconds. The
abdomen is soft and nontender. Laboratory examination shows: serum sodium, 125 mEq/L (125 mmol/L);
potassium, 3.8 mEq/L (3.8 mmol/L); chloride, 85 mEq/L (85 mmol/L); and bicarbonate, 30 mEq/L (30 mmol/
L). Venous blood pH is 7.48 and PCO2 is 55 torr. Blood urea nitrogen (BUN) is 48 mg/dL (17.1 mmol/L).
Urine output is decreased. Which of the following is the most likely diagnosis?
A.
B.
C.
D.
E.
Congenital adrenal hyperplasia.
Hypertrophic pyloric stenosis.
Malrotation of intestine.
Milk allergy.
Obstructive uropathy.
7. A 3-month-old boy presents with vomiting and diarrhea for the past 3 days. He recently was switched
from human milk to powdered milk formula. Physical examination shows a markedly irritable infant who
has a heart rate of 170 beats/min, respirations of 50 breaths/min, temperature of 99.7°F (37.6°C), and
blood pressure of 60/30 mm Hg. The anterior fontanelle is markedly depressed, and mucous membranes are
dry. The skin has diminished turgor, with tenting and a doughy feel. The capillary refill time is 4 to
5 seconds. Bladder catheterization yields no urine output. Laboratory values are: serum sodium, 172 mEq/L
(172 mmol/L); potassium, 5.3 mEq/L (5.3 mmol/L); chloride, 148 mEq/L (148 mmol/L); and bicarbonate,
8 mEq/L (8 mmol/L). BUN is 72 mg/dL (25.7 mmol/L). Which of the following is the best management
strategy for this child?
A.
B.
C.
D.
E.
An intravenous bolus of 5% dextrose followed by rehydration over 48 hours.
An intravenous bolus of 5% dextrose followed by rehydration over 24 hours.
An intravenous bolus of 0.9% saline followed by rehydration over 48 hours.
An intravenous bolus of 0.9% saline followed by rehydration over 24 hours.
Rehydration over 48 hours without intravenous bolus.
8. Which of the following states is associated with greater fluid loss per kilogram of body weight for a given
severity of clinical manifestations of dehydration in children?
A.
B.
C.
D.
E.
Fever.
Hypernatremia.
Male gender.
Obesity.
Older age.
Please note that the deadline for submission of your answer sheets
for the quizzes in the 2002 issues has been extended to January 31,
2003!
282 Pediatrics in Review Vol.23 No.8 August 2002