Pediatric Fluids and Electrolytes

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Pediatric Fluids and Electrolytes

• Katinka Kersten

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Learning Objectives

• Recognize that fluid and electrolyte homeostasis
  is different in infants, children and adults
• Know contents of different fluid compartments in
  body
• Know how to estimate maintenance fluid and
  electrolyte needs
• Know fluid management for patients with
• Isonatremic dehydration
• Hyponatremic dehydration
• Hypernatremic dehydration
• Know contents of different intravenous and oral
  rehydration solutions

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ECF and ICF

• Body has two fluid compartments
• Extracellular fluid (ECF) space makes up 1/3 of
  our body fluids
• Intracellular fluid (ICF) space makes up 2/3 of
  our body fluids
• Extracellular space refers to fluids outside our
  cells which may be interstitial fluid or plasma
  or
• CSF
• Total body water 0.6 X weight (kg) for children
  and adults and 0.78 X weight (kg) for neonates
  and infants

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ECF and ICF Composition
ICF (mEq/L) ECF (mEq/L) Sodium 20
135-145 Potassium 150 3-5
Chloride --- 98-110 Bicarbonate 10 20-25 Pho
sphate 110-115 5 Protein 75 10
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Approach to Fluid Calculations

• 1. Maintenance Determined by a system
• a. Caloric expenditure method
• b. Holliday-Segar method c.
  Surface area method
• 2. Deficit Determined by acute weight
  change or clinical estimate
• 3. Ongoing losses Determined by measuring

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• MAINTENANCE FLUIDS

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Basal Metabolism

• Daily fluid and electrolyte need is related to
  daily average energy requirement.
• Daily energy requirement is determined by Resting
  Energy Expenditure (REE) plus correction factor
  for activity, fever, trauma, injury and growth.
• The two by-products of metabolism are heat and
  solute
• Heat is dissipated by evaporation of water from
  the skin surface and with exhalationINSENSIBLE
  LOSSES
• Solute, or soluble waste losses are excreted in
  the urine

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Resting Energy Expenditure

• Expressed in units of energy (kcal)
• Is not directly related to weight
• When compared to body weight the Resting Energy
  Expenditure (REE) is high in the newborn, and
  lower in adults and energy needs/kg are therefore
  highest in infants.
• Adolescents and adults have lower REE than
  generate less heat and solute from basal
  metabolism than do children or infants. So, they
  also need less fluid and electrolytes per unit of
  body weight.

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Maintenance Fluid Simplification

• Its difficult to remember Resting Energy
  Expenditure and average daily energy needs for
  different ages and sizes and most people rely on
  existing tables.
• Two systems have been proposed to relate
  maintenance fluid and electrolyte needs to the
  body weight.
• Surface area method
• Holliday-Segar method

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Holliday-Segar Method

• Most widely used method
• Landmark paper by Holliday and Segar in 1957
• Assumes that for each 100 calories metabolized,
  100 ml H2O will be required (50 ml/100 calories
  for insensible loss, 67 ml/100 calories for urine
  and 17 ml/100 calories gained from metabolism)
• Not suitable for newborns

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Holliday-Segar

• FLUID REQUIREMENTS
• For first 10 kg 100 ml/kg/day (4ml/kg/hr)
• For second 10 kg 50 ml/kg/day (2ml/kg/hr)
• Each additional kg 20 ml/kg/day (1ml/kg/hr)
• ElECTROLYTE REQUIREMENTS
• Na 3 mEq/100ml
• Cl- 4 mEq/100ml
• K 2 mEq/100ml
• This method recently being challenged by several
  papers it is felt that maintenance sodium needs
  are much higher in sick children because of
  increased ADH secretion with many common
  pediatric illnesses

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Modifications for Maintenance Fluids
Increase Decrease _____________________________
__________ Fever Renal failure High ambient
temperature Postoperative Diabetes
mellitus Heart failure Diabetes
insipidus Inappropriate secretion Vigorous
exercise of ADH High-humidity
respiratory therapy
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• REPLACEMENT OF DEFICIT

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ECF and ICF percentage of loss
If losses occur over very short period most of
the loss is from ECF If losses occur over long
period of time losses are about 50/50 ICF and
ECF
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Clinical signs of Dehydration
Type Percent Symptoms Very mild lt3 Thirst
may be present Mild 3-5 Dry mucous membranes
and conjunctiva Moderate 5-7 Sunken eyes,
decreased fontanelle Severe 7-12 Tenting
of skin Very severe gt12 Shock
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ECF and ICF Composition
ICF (mEq/L) ECF (mEq/L) Sodium 20
135-145 Potassium 150 3-5
Chloride --- 98-110 Bicarbonate 10 20-25 Pho
sphate 110-115 5 Protein 75 10
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Isotonic dehydration (Na 130-145 mEq/L)
A 2 year old has a 5-day history of
gastroenteritis, poor fluid intake and
infrequent urination. On exam you find dryness
of the mucous membranes, sunken eyes with mild
tenting of the skin. The serum sodium is 137
mEq/L. The weight is 10 kg. You determine the
child is suffering from about 10 dehydration. Wh
at are the fluid and electrolyte requirements?
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Isotonic Dehydration Example
H2O Na K (ml)
(mEq) (mEq) Maintenance Total deficit
1000 ml Extracellular fluid deficit (50 of
total) Intracellular fluid deficit (50 of
total) Total
1000 30 20
500 70
500 75
2000 100 95
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Hypertonic Dehydration (Na gt 145 mEq/L)

• Mortality can be high
• Often iatrogenic
• The intravascular volume(extracellular space) is
• preserved at the expense of the intracellular
  volume
• The patient looks better than you would expect
• based on fluid loss
• Always assume total fluid deficit of at least 10

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Free Water Deficit
Use 4 ml/kg of body weight for each mEq of
Na above 145 mEq/L as the Free Water
Deficit (Serum Na -145 mEq/) x weight x 4
total amount of free water needed to dilute the
serum to get a normal concentration Na Only
correct half of total Free Water Deficit in first
24 hours if Na lt 175 mEq/L For Na gt 175 mEq/L
you do not want to correct faster than 1 mEq/L/hr
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Hypertonic Dehydration Example
6-month-old suffering for 4 days from
severe diarrhea. Mucous membranes are dry, skin
feels doughy and the child is somnolent and
lethargic. The serum Na is 165 mEq/L. The child
weighs 5 kg and you assume the fluid deficit is
at least 10. What are the fluid and electrolyte
requirements?
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Hypertonic Dehydration Example
H2O Na K (ml) (mEq)
(mEq) Maintenance Total deficit 500 ml ½ of
Free Water Deficit (165-145)x5x4x½ Remainder
of deficit (500-200) 300 ml Extracellular
(60) Intracellular (40) Total
500 15 10
200
180 25
120 18
1000 40 28
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Hypotonic Dehydration (Na lt 135 mEq/L)

• Children with vomiting and diarrhea who have
  received
• hypotonic fluids as oral replacement
• Shock is an early symptom.
• Physical exam findings usually exaggerate
• amount of dehydration.

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Additional Na needed

• To calculate the Na Deficit, multiply 0.6 mEq/kg
  of body weight for each mEq of Na below 135
  mEq/L.

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Hypotonic Dehydration Example
A 3-year-old has had diarrhea and vomiting for 1
day. Examination shows sunken eyes and marked
tenting of the skin but the child is not in
shock. The serum Na is 120 mEq/L. The weight 14
kg. You estimate the deficit as 7. What are
the fluid and electrolyte requirements for this
patient?
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Hypotonic Dehydration Example
H2O Na K (ml) (mEq) (mEq) Maintena
nce Deficit (7 of 14 kg) Extracellular
fluid (80) Intracellular fluid
(20) Additional sodium (135-120) x 0.6 x
14 Total
1200 36 24
800 112
200 30
126
2200 274 54
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Electrolytes in Body Fluids (mEq/L)
Na K Cl HCO3 Gastric juice 140 15 155 0 Small
-intestinal juice 140 15 155 40 Diarrhea 40 40 4
0 40 Sweat 70 15 60 0
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Composition of Parenteral Fluids
Fluid cal/L Na K CL HCO3 D5W 170
0 0 D10W 340 0 0 NS 0
154 154 1/2 NS 0 77 77 D5 1/4 NS 170
34 34 LR 0 130 4 109 28 Alb.
25 1000 100-160 lt120
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Electrolytes in Popular Drinks
Na (mEq/L) K (mEq/L) Apple juice 0.4
26 Coke 4.3 0.1 Gatorade 21
2.5 Milk 22 36 OJ 0.2
49 Pedialyte 45 20 WHO ORS 90 20