Potential Renal Solute Load

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Potential Renal Solute Load
2
Potential Renal Solute Load

• Solutes of dietary origin that would need to be
  excreted in the urine if none were diverted into
  synthesis of new tissue and none were lost
  through non-renal routes

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Normal, Healthy Infants

• Renal solute load is not a problem
• During illness, water losses are increased due to
  fever, diarrhea, vomiting GREATER WATER LOSS
• And intake of fluids is often less a sick baby
  doesnt want to consume breastmilk or formula
  LESS WATER INTAKE

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What is a risky PRSL?

• During illness PRSL of 39 mosmol/100 kcal or 260
  mosm/L increases risk of hypertonic dehydration
• Upper limit of PRSL 33 mosmol/100 kcal or 220
  mosmol/L
• Lower is safer with respect to water balance

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PRSL Determination

• PRSL N/28 Na Cl K Pa
• N units in mg other Units are in mmol (or mosmol)
  mmol meq/valence or meq valence x mmol
• N/28 represents excretion of N substances (with
  the assumption that the number of N atoms per
  molecule is 2)
• Pa is available phosphorus. Phytate P is not
  available for absorption. In soy-based formulas,
  30 of P is phytate bound and does not contribute
  to P in circulation and filtered by the kidney.
  Other non-soy formulas all P is available

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Milligrams to mEq

• Milligrams/ atomic wt x valence meq
• Example Phosphorus 280 mg / 31 mg/mmol x 2 18
  meq
• Example Na 162 mg/23 x 1 7 meq

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Examples

• Similac cows milk based formula
• 680 Kcal/Liter
• N Protein 14 g/6.25 g Pro per gr N 2.24 g N
  2240 mg N/2880
• 162 mg/23 mg/meq 7.0 meq Na 7 mmol
• mg Cl Not given but can be estimated 7
  meq7mmol

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Calculations (cont)

• K 710 mg/39 mg/meq 18 meq K 18 mmol
• 280 mg/ 31mg/meq 9 meq P X 2 18 mmol (P has
  valence of 2) In Cows milk formula all P is
  available

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Na to NaCl to Cl

• Na has atomic wt of 23
• Cl has atomic wt of 35.4
• If you have wt of 162 mg Na that would mean that
  an equivalent amount of Cl was also added or
  about 162/23 x/35.4 249 mg Cl 7 meq Cl

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Calculations

• PRSL N/28 Na Cl K P
• 80 7 7 18 18 130 mmols per Liter
• There are 680 Kcal / liter
• 130 / 6.8 19 mosmol/100 Kcal
• Which is under the 33 mosmol/100 kcal limit

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Situation Infant needs more kcals

• Powdered Formula how much can you mix and not
  cause problems with osmolality fluid shifts
  renal solute load in ill infant?
• Example Similac has PRSL of 19 mosmol/100
  kcal. If want to increase to upper limit of
  acceptable 33
• 33/19 1.7 times concentration so you can add
  about 1.7x the amount called in recipe

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Powdered formula

• Directions for mixing
• 4 oz of formula 4 fl oz of water 2 unpacked
  level scoops
• Upper limit of acceptable PRSL?
• 4 oz of formula 4 fl oz 4 scoops of unpacked
  level scoops
• Results in 34 mosmols/ 100 kcal
• Increase gradually!! And check for tolerance!!

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Foman S.J. Potential Renal Solute Load
Considerations Relating to Complementary Feedings
of Breastfed Infants. Pediatrics 106(5) Nov 2000
p 1284

• Intro When an infant is well and consuming a
  predominantly liquid diet, the renal
  concentrating ability in nearly all infants is
  sufficient to maintain water balance even with
  PRSL of cows milk.
• PRSL is important to consider when
• 1. Acute illness 2. When energy dense diet is fed
  3. When kidney isnt working well

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PRSL of Infant Foods

• PRSL
• Mosmol/L mosm/100 kcal
• Human Milk 93 14
• Formula 135-260 20-39
• Cow milk 308 46
• Beikosta 153 23
• a any non-milk food

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Hot Environments

• Nearly all breastfed infants maintain water
  balance in hot environments.

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Water Balance in illness

• Replacing human milk with beikost has a slightly
  negative affect on water balance in 6 month old.
• Slightly increasing Human milk or beikost in
  illness has a slightly positive effect on water
  balance.
• Therefore in illness of infant, important to
  increase total volume of intake(fluid beikost)