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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Developmental Differences in Children

• Increased fluid intake and output relative to
  size. Total body fluid of infants is 20 more
  than adults
• Greater surface area relative to size and
  therefore more water loss through skin
• Increased metabolic rate
• Immature kidney function that requires more fluid
  to excrete waste

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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
• LOW AMOUNT OF ELECTROLYTES IN FLUID
• 2. Deficit Determined by acute weight
  change or clinical estimate
• HIGH AMOUNT OF ELECTROLYTES IN FLUID
• 3. Ongoing losses Determined by measuring

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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.
• When compared to body weight the Resting Energy
  Expenditure (REE) is high in the newborn, and
  lower in adults

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Maintenance Fluid Simplification

• Its impossible to know 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
• Studies done on healthy infants and children
• 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

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• REPLACEMENT OF DEFICIT

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ECF and ICF Contributions to 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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Oral Rehydration Therapy

• Safest way to rehydrate patient is by the enteral
  route
• Best to use ORS as this is least hyponatremic.
  However many patients dont take this because
  salty. Pedialyte decent as well and thirdly
  Gatorate
• Can not do this in patients with
• Severe altered mental status
• Persistent severe vomiting
• Intestinal obstruction

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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
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Isotonic dehydration (Na 130-145 mEq/L)
A 2 year old has a 6-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 (Holiday/Segar) Tot
al 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 3 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 (Holiday/Segar) 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 (Holliday/Segar) 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