Fluid and Electrolyte Therapy
in the Pediatric Patient
Steve Piecuch MD, MPH
Department of Pediatrics
Lincoln Medical Center
Maintenance Requirements
Introduction to the Principles of Fluid and
Electrolyte Therapy
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Important to understand the underlying physiologic
principles of a therapy commonly employed in pediatrics
Understanding basic principles essential for the
understanding of the management of more complex
disorders such as:
– Cholera
– Dengue
– Pyloric stenosis
– DKA
– Hyperosmotic non-ketotic coma
Crystalloid and Colloid
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Crystalloid: Water and electrolyte solution
» Does not remain within the intravascular space but rather
distributes to the entire extracellular space
» Only impacts on the intracellular space if it causes a change in
extracellular osmolarity
– E.g.: 0.9% NaCl, D5 0.3% NaCl
Colloid: Contains large particles which tend to remain within the blood
vessels
» Colloid preferentially expands the intravascular space because
the particles exert oncotic force which retains water within the
intravascular space
– E.g.: 5% albumin, blood, dextran solution
Isotonic Saline Solution
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Isotonic saline solution: Solution such as 0.9% NaCl or
Ringer’s lactate with a Na concentration similar to that of
plasma water
– Crystalloid distributes throughout the extracellular space
– Infusion of crystalloid will cause a fluid shift into or out
of the intracellular space only if it creates an osmotic
gradient between the extracellular and intracellular space
– Isotonic saline does not change the osmolarity of the
extracellular space
– Therefore: Isotonic saline solution remains within and
expands the extracellular space and has minimal effect on
the intracellular space
Maintenance Fluid and Electrolyte
Requirements
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Maintenance: The replacement of normal ongoing losses
– Normally serum Na concentration is approximately 140
meq/l and serum K concentration is approximately 4 meq/l
– Maintenance solution replaces normal losses
– Maintenance solution does not have an electrolyte
concentration equal to serum because the electrolyte
composition of urine and stool is not equal to that of serum
Maintenance fluids commonly provided as a 5% dextrose
solution
– Dextrose provides some energy and prevents hypoglycemia
» Spares protein
– Cannot meet patient’s nutritional requirements with 5% (or
10%) dextrose
Maintenance Requirements are a Function of
Caloric Requirements
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0-10 kg:
100 kcal/kg
10-20 kg: 50 kcal/kg
> 20kg:
20 kcal/kg
Examples:
– 8 kg: 8 kg X 100 kcal/kg = 800 kcal.
– 12 kg: 10 kg X 100 kcal/kg + 2 kg X 50 kcal/kg = 1000
kcal + 100 kcal = 1100 kcal
– 20 kg: 10 kg X 100 kcal/kg + 10 kg X 50 kcal/kg =
1000 kcal + 500 kcal = 1500 kcal
– 25 kg: 10 kg X 100 kcal/kg + 10 kg X 50 kcal/kg + 5
kg X 20 kcal/kg = 1000 kcal + 500 kcal + 100 kcal =
1600 kcal
Water and Electrolyte Requirements are
Determined by Caloric Requirements
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Requirements per 100 kcal:
– 100 ml water (provided as a 5% dextrose solution)
– 2-4 meq Na
– 2 meq K
– 2 meq Cl
Plasma: Anion is a balance of Cl and base (bicarbonate)
– Maintenance solution: Can provide some anion as Cl
and some as base (lactate, citrate, phosphate) or can
provide all of it as Cl
– But: Providing large volumes of fluid (e.g., in DKA or
hypovolemic shock) with all of the anion as Cl will
promote a hyperchloremic metabolic acidosis
Standard Maintenance Solution
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D5W with 20-40 meq/l Na Cl and 20 meq/l KCl (or
KAcetate or KPhosphate) will work well as a maintenance
solution in most pediatric patients
– Can use D5 0.2% (or D5 0.3%) NaCl with 20 meq/l KCl (or
KAcetate or KPhosphate) as maintenance solution
– Recent article advocated routine use of isotonic saline
solution for pediatric maintenance solution
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Some disease states: Another solution might be appropriate
– E.g.: Sickle cell anemia patients may have a relatively high
Na requirement due to high urinary Na losses
– 0.9% NaCl (without dextrose) in head trauma patients
– K should be used with caution or omitted in patients with
renal insufficiency
Water and Electrolyte Requirements Based on
Weight
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Water:
– 0-10 kg: 100 ml/kg
– 10-20 kg: 1000 ml plus 50 ml/kg
– > 20 kg: 1500 ml plus 20 ml/kg
Electrolytes:
– Na: 2-3 meq/kg
– K: 1-2 meq/kg
Water requirement is the same as with the caloric-based
system
Electrolyte requirement is greater than with caloric-based
system: Electrolyte requirement is a direct linear function
of weight
Routine Use of D5 0.45% NaCl as
Maintenance Solution in Older Patients
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Calculate water and electrolyte requirements on a per 100 kcal
basis: Relationship between water and electrolyte requirements
is fixed and does not change as weight increases
But: If the water requirement is calculated on a per 100 kcal
basis and the Na requirement is calculated on a per kg basis,
then as the patient’s weight increases the Na requirement will
increase at a greater rate than the water requirement
– Heavier children will require a maintenance solution with a
higher Na concentration
Why: Because the water requirement does not increase linearly
as weight increases: As weight increases the water requirement
as expressed on a per kg basis decreases
Routine Use of D5 0.45% NaCl as
Maintenance Solution (Continued)
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Consider Na concentration of maintenance solution if
estimate Na requirement to be 3 meq/kg (not 2-4 meq/100
kcal)
– 10 kg: 30 meq Na in 1000 ml: 30 meq /l:
– 20 kg: 60 meq Na in 1500 ml: 40 meq/l
– 40 kg: 120 meq Na in 1900 ml: 63 meq/l
– 70 kg: 210 meq Na in 2500 ml: 84 meq/l
This explains why commercially available maintenance
solutions exist which are designed for children below and
above a specific weight
– Remember discussion about providing some anion as
base: This explains why commercial solutions may
contain some anion in the form of lactate or citrate
Dehydration
Dehydration
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Good working definition in pediatrics: Loss of body fluid,
usually predominantly from the extracellular space, due to
decreased intake and/or increased losses
– Most common cause is probably acute gastroenteritis
– Failure to replace fluids lost from ostomies and drains
with an appropriate solution may cause significant
electrolyte imbalance and dehydration
Patients with apparently acceptable intake may develop
significant fluid and electrolyte imbalances
– E.g.: Infant with a ventricular drain will lose a
significant amount of Na in the ventricular fluid
» Such an infant may develop severe hyponatremia if
exclusively fed human milk (low Na)
Classify Dehydration as to Type
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Isonatremic dehydration: Serum Na between 130 meq/l
and 150 meq/l
Hyponatremic dehydration: Serum Na < 130 meq/l
Hypernatremic dehydration: Serum Na > 150 meq/l
Serum Na and osmolarity
– Hypernatremic patients are always hyperosmolar
– Isonatremic patients are not always isoosmolar
» E.g.: Serum Na 140 meq/l and glucose 600 mg/dl
– Hyponatremic patients are not always hypoosmolar
» E.g.: Serum Na 129 meq/l and glucose 800 mg/dl
– Note: Isonatremic or hypernatremic patient with normal
glucose may be hyperosmolar due to mannitol
Ongoing Abnormal Losses
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Maintenance solution is designed to replace ongoing
normal losses
Ongoing abnormal losses: Diarrhea, ostomy drainage,
chest tube drainage, ventricular fluid drainage
Possible to measure electrolytes in the fluid but is usually
unnecessary
– May be useful if there is a large volume of drainage
accompanied by significant electrolyte imbalance
Nasogasric drainage: 0.45% (or 0.9%) NaCl with 20-40
meq/l KCl
Ileostomy drainage: 0.9% NaCl with 10-20 meq/l KCl or
KAcetate
Clinical Findings in Dehydration
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History: Refusal to feed, vomiting, diarrhea, decreased
urine output
– Increased risk: Children with defective thirst
mechanism, DI, impaired access to water
Physical: Sunken fontanel, decreased tears, decreased
skin turgor, tachycardia, weak pulses, cool extremities
– Hypotension is a late finding which occurs only after
compensatory mechanisms have failed
Laboratory: Metabolic acidosis, increased BUN,
increased creatinine, increased urine specific gravity
Classify Dehydration as to Severity
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Mild: Earliest signs of dehydration
– 30-50 ml/kg deficit (3-5% dehydration)
Moderate: Signs of dehydration more pronounced
– 60-100 ml/kg deficit (6-10%)
Severe: Impending or actual circulatory failure
– 90-150 ml/kg deficit (9-15%)
Smaller children (e.g., < 2 years old) use 5%-10%-15%
dehydration
In larger children (e.g., > 2 years old) use 3%-6%-9% rather than
5%-10%-15% to avoid providing excessive volumes of fluid
Alternative approach: IV rate of one and a half maintenance for
mild to moderate dehydration and twice maintenance for moderate
to severe dehydration
Severity (Continued)
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Can use weight change to estimate the volume of the
deficit if the change is recent (i.e., over 24 hours) and you
are confident that the weights are reliable
– Recent weight loss implies predominantly a water loss
Degree of dehydration is an estimate, not precise
(analogous to a visual estimate of serum bilirubin)
Initially underestimating the degree of dehydration is not
harmful so long as any existing or impending circulatory
failure is recognized and treated appropriately
Initially overestimating the degree of dehydration is not
harmful so long as the overestimate is recognized and the
fluid regimen is appropriately adjusted
Isonatremic Dehydration
Traditional Management of Isonatremic
Dehydration
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24 hour repair: Provide the deficit and one day’s
maintenance over a 24 hour period
Give half the total in the first 8 hours
– Volume of fluid given during an emergency phase (i.e.,
bolus) is included as part of the first 8 hour’s fluids
The second half is given over the remaining 16 hours
Emergency phase: One or more 20 ml/kg boluses of 0.9%
NaCl in moderate to severe dehydration
Repair solution: Maintenance and deficit requirements
combined
– In isonatremic dehydration can use D5 0.45% (or 0.3%)
NaCl with 20 meq/l KCl (or KAcetate)
Repair of Isonatremic Dehydration (Example)
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21 kg patient with 10% dehydration
Total 24 hour requirement: 3620 ml
» Maintenance: 1520 ml
» Deficit: 2100 ml
– 1810 ml in first 8 hour and 1810 ml in next 16 hours
Emergency phase: 2 isotonic saline boluses for a total of
40 ml/kg (840 ml) over 1 hour
Repair solution: D5 0.45% NaCl with 20 meq/l KCl
– 1810 ml – 840 ml: 970 ml over next 7 hours: 139 ml/hr
– 1810 ml in next 16 hours: 113 ml/hr
Repair Solution in Isonatremic Dehydration:
Assumptions
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Deficit is primarily from the extracellular space
Serum Na concentration unchanged:
– Therefore the deficit must have Na concentration
approximately equal to that of plasma water: 150 meq/l
– Na concentration of plasma water is higher than that of
serum because serum contains solids such as albumin which
reduce the Na concentration
Ignore component of the deficit which consists of intracellular
fluid with a low Na and a high K concentration
Ignore maintenance electrolyte requirements because they are
relatively insignificant compared with the deficit electrolyte
requirements
– Some authorities include the maintenance electrolytes in
their calculations
Repair Solution in Isonatremic Dehydration
(Continued)
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10 kg patient with 5% dehydration:
» Maintenance: 1000 ml water
» Deficit: 500 ml water and 75 meq Na
– 1500 ml water and 75 meq Na: 0.3 % NaCl
10 kg patient with 10% dehydration:
» Maintenance: 1000 ml water
» Deficit: 1000 ml water and 150 meq Na
– 2000 ml water and 150 meq Na: 0.45% NaCl
Remember: Na deficit exists and must be replaced in
isonatremic dehydration even though serum Na is normal
– Na deficit: Na component of the isotonic volume loss
Repair Solution in Isonatremic Dehydration
(Continued)
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D5 0.45% (or D5 0.3%) NaCl with 20 meq/l KCl or
KAcetate works well as a repair solution
The Na requirement is determined by the deficit
The greater the deficit relative to the maintenance
requirements, the greater the Na concentration needs to be
– Moderate to severe dehydration: D5 0.45% NaCl
preferred over D5 0.3 % NaCl
Chronic dehydration associated with a significant
intracellular loss: Some patients may develop hypokalemia
and require 30-40 meq/l of K in the repair solution
Actual Calculations: Modified Finberg
Technique
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Example: 12 kg patient with 10% isonatremic dehydration
– Maintenance volume: 1100 ml
– Deficit volume: 1200 ml
– Deficit Na: 1.2 liters X 150 meq/l = 180 meq
Repair the dehydration: Give 2300 ml of water and 180
meq of Na over a 24 hour period
Technique: Give half over first 8 hours and the remainder
over the next 16 hours
– Give 20 ml/kg isotonic saline bolus if have deficit >
10%
Modified Finberg Technique (Continued)
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12 kg patient with 10% dehydration: Require 2300 ml of water and
180 meq of Na over a 24 hour period
Emergency phase: 20 ml/kg X 12 kg = 240 ml of 0.9% NaCl
» 240 ml of water
» 37 meq of Na
Repair solution
» Water: 2300 ml - 240 ml = 2060 ml
» Na: 180 meq - 37 meq = 143 meq
» 2060 ml of water with 143 meq of Na
» 5% dextrose solution with 69 meq/l of Na
Give 1150 ml over first 8 hours and 1150 ml over following 16 hours
– 1150 ml – 240 ml (bolus) = 910 ml
» 910 ml/8 hr = 113.8 ml/hr
– 1150 ml/16 hr = 71.8 ml/hr
Summarize: 12 kg patient with 10%
Isonatremic Dehydration
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Emergency phase: 20 ml/kg of isotonic saline
» 240 ml of 0.9% NaCl
» Dextrose free fluid bolus: Correct hypoglycemia
separately if necessary
Repair solution: 5% dextrose solution with 69 meq/l of Na
– D5 0.45% NaCl close enough (77 meq/l Na)
» Repair solution should include 20-40 meq/l of K to
meet K needs and to replace any intracellular deficit
– First 8 hours: 2300 ml/2 = 1150 ml - 240 ml = 910 ml/8
hr = 114 ml/hr
– Subsequent 18 hours: 1150 ml/16 hours = 72 ml/hr
Alternative Approaches to the Repair of
Isonatremic Dehydration
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Give maintenance evenly over 24 hours but give half the deficit
over the first 8 hours and the rest of the deficit over the next 16
hours
– Complicated: Either use different IV bags for the
maintenance and deficit fluids or change the electrolyte
composition of the repair solution after the first 8 hours
Estimating relative contributions of the extracellular and
intracellular fluid to the overall deficit
» Extracellular fluid: Na concentration of 150 meq/l
» Intracellular fluid: K concentration of 150 meq/l
– Unnecessary if K is provided in repair solution and is
increased if hypokalemia develops during the repair
Alternative Approaches to the Repair of
Isonatremic Dehydration (Continued)
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Give one or more 20 ml/kg boluses of isotonic saline as needed
and then run D5 0.45% (or 0.3%) NaCl at 1.5 or 2 times
maintenance
– Commonly done, not an unreasonable approach
– Remember: Na concentration of D5 0.45% and D5 0.3%
NaCl is significantly greater than maintenance requirements
– True maintenance solution contains inadequate Na to
effectively correct significant isonatremic dehydration
Rapid correction of the deficit over less than 24 hours
– E.g.: Give 100 ml/kg of isotonic saline solution over 3-6
hours to replace the deficit
» Provide maintenance separately or by the oral route
– May avoid hospitalization or shorten hospital stay
Correction of Abnormal Osmolarity
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So long as actual or impending circulatory failure is treated
appropriately with isotonic saline solution, the kidney will
usually compensate if the degree of the water or Na deficit
is underestimated or overestimated
– Excessive urine output: May be a protective measure in
a patient who is being rehydrated at an excessive rate
Rapid correction of abnormal osmolarity
– Potentially harmful
» Hyponatremia: Central pontine myelinolysis
» Hypernatremia: Seizures
» DKA: Cerebral edema
– Kidney will not protect against this