Fluid and Electrolyte Therapy in the Pediatric Patient

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Fluid and Electrolyte Therapy in the Pediatric
Patient

• Steve Piecuch MD, MPH
• Department of Pediatrics
• Lincoln Medical Center

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• Maintenance Requirements

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Introduction to the Principles of Fluid and
Electrolyte Therapy

• 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

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Crystalloid and Colloid

• 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

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Isotonic Saline Solution

• Isotonic saline solution Solution such as 0.9
  NaCl or Ringers 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

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Maintenance Fluid and Electrolyte Requirements

• 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 patients nutritional requirements
  with 5 (or 10) dextrose

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Maintenance Requirements are a Function of
Caloric Requirements

• 0-10 kg 100 kcal/kg
• 10-20 kg 50 kcal/kg
• gt 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

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Water and Electrolyte Requirements are Determined
by Caloric Requirements

• 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

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Standard Maintenance Solution

• 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
• 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

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Water and Electrolyte Requirements Based on Weight

• Water
• 0-10 kg 100 ml/kg
• 10-20 kg 1000 ml plus 50 ml/kg
• gt 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

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Routine Use of D5 0.45 NaCl as Maintenance
Solution in Older Patients

• 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
  patients 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

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Routine Use of D5 0.45 NaCl as Maintenance
Solution (Continued)

• 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

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• Dehydration

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Dehydration

• 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)

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Classify Dehydration as to Type

• Isonatremic dehydration Serum Na between 130
  meq/l and 150 meq/l
• Hyponatremic dehydration Serum Na lt 130 meq/l
• Hypernatremic dehydration Serum Na gt 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

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Ongoing Abnormal Losses

• 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

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Clinical Findings in Dehydration

• 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

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Classify Dehydration as to Severity

• 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., lt 2 years old) use
  5-10-15 dehydration
• In larger children (e.g., gt 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

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Severity (Continued)

• 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

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• Isonatremic Dehydration

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Traditional Management of Isonatremic Dehydration

• 24 hour repair Provide the deficit and one days
  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
  hours 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)

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Repair of Isonatremic Dehydration (Example)

• 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

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Repair Solution in Isonatremic Dehydration
Assumptions

• 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

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Repair Solution in Isonatremic Dehydration
(Continued)

• 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

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Repair Solution in Isonatremic Dehydration
(Continued)

• 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

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Actual Calculations Modified Finberg Technique

• 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 gt 10

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Modified Finberg Technique (Continued)

• 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

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Summarize 12 kg patient with 10 Isonatremic
Dehydration

• 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

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Alternative Approaches to the Repair of
Isonatremic Dehydration

• 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

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Alternative Approaches to the Repair of
Isonatremic Dehydration (Continued)

• 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

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Correction of Abnormal Osmolarity

• 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