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PA30304 > Parenteral nutrition > Flashcards

Parenteral nutrition Flashcards

1
Q

Who needs PN?

A

Pre-term infants: short term support until neonate can feed orally

GI failure - bowel obstruction, short bowel

GI support - crohns disease, multiple trauma, pseudo-obstructions, short term gut rest

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2
Q

What is the primary goal of PN?

A

Provide adequate calories and proteins whilst maintaining fluid balance

Prevent malnutrition and associated complications.

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3
Q

What is PN?

A

PN is an infusion of a stable mixture of nearly ALL nutrients in soluble form. Contains:

  • proteins as amino acids
  • carbohydrate as glucose
  • fat as oil in water emulsion
  • electrolytes
  • trace elements
  • vitamins A, B, C, D E
  • water
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4
Q

What is in a TPN bag?

A

Macronutrients - AA, carbohydrates, lipids, electrolytes

Micronutrients - trace elements, vitamins

Water

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5
Q

Macro and micro nutrients refer to what?

A

The volume which they come in

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6
Q

What is a triple chamber bag?

A

Separate glucose, amino acid and lipid

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7
Q

What is and 2 in 1 PN bag?

A

Aqueous ingredients only. Lipids are separate to aide stability.

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8
Q

What is a 3 in 1 PN bag?

A

All ingredients are in one bag

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9
Q

What is a 1 in 1 PN bag?

A

Amino acid and electrolyte replacement

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10
Q

How does sunlight affect stability of a PN bag?

A

Break down of vitamin A when exposed to sunlight

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11
Q

How can entrained air affect the stability of a PN bag?

A

Formation of lipid peroxidase when the lipid emulsion is exposed to oxygen and sunlight.
These breakdown products are chemically very reactive and could be harmful.

Oxidation of amino acids - tryptophan, tyrosine etc. Tryptophan degradation products might cause cholestasis and possibly neurotoxic

Break down of vitamin C

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12
Q

Oxidation of tryptophan can cause what?

A

Tryptophan degradation products might cause cholestasis and possibly neurotoxic

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13
Q

What is the result of vitamin C oxidation?

A

Copper catalyses the break down of vitamin C. Can lose up to 50% in a few days and breakdown product precipitates with Ca2+.

Oxidised to oxalic acid which can precipitate with calcium.

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14
Q

What are the issues associated with precipitation in PN bags?

A

Can block small capillaries e.g. in the lungs and other organs

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15
Q

When might ppt occur?

A

Can occur when adding strong injections of Ca/Mg/Phosphate to the PN without mixing between additions or without diluting the solutions before filling into the PN bag.

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16
Q

The solubility of Ca and Phosphate salts can be influenced by what?

A

Dibasic salts are less soluble than mono salts.
Concentration
pH
Other ingredients

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17
Q

How can the addition of other ingredients increase the solubility of Ca and Po?

A

Use of lower pH aa sources
increased aa conc
organic source of Ca or Po4

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18
Q

The final pH of PN mixtures should be maintained at pH what?

A

5.0 or above (and below 6 to reduce ppt)

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19
Q

How can the compounding process influence ppt?

A
  1. Storage temperature - ppt more likely as temperature rises. (but need to warm up slightly before admin)
  2. Time after manufacturer
  3. Use in-line filters
  4. Use organic divalent components e.g sodium glycerophosphate, calcium gluconate. AVOID INORGANIC
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20
Q

Why do we favour the use of organic Ca and PO4 salts?

A

Inorganic are less soluble and more likely to ppt.

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21
Q

Addiphos

A

Inorganic

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22
Q

Sodium glycerophosphate

A

Organic

23
Q

Calcium gluconate

A

Organic

24
Q

Calcium chloride

A

Inorganic

25
Q

Magnesium sulphate

A

Inorganic

26
Q

Outline how dilution and order of mixing should be carried out to avoid ppt in a PN bag?

A

Add macro-electrolytes (Na, K) to amino acids

Separate and dilute calcium and phosphate components before mixing - form chelates by PO4 to glucose and Ca to amino acids

Mix amino acids and glucose before adding lipid.

27
Q

PO4 should be chelated to what?

A

Glucose

28
Q

Ca should be chelated to what?

A

Amino acids

29
Q

What component should be added to a PN bag last?

A

Lipids

30
Q

Vitamins should be added to what?

A

Lipid

31
Q

Trace elements should be added to what?

A

Glucose or in late order (as want to keep copper separate from vitamins)

32
Q

What should trace elements be added to a PN bag as late as possible?

A

Want to avoid copper from catalysing the oxidation of vitamin C

33
Q

Why do we not want very high glucose concentrations?

A

High concentrations (40-50%) destabilise fat emulsions as lowers the pH - lipids favour high pH so destabilise.

Lower pH promotes monobasic calcium phosphate (more soluble)

Hyperglycemia risk

34
Q

What is the max conc. of glucose what is suitable for peripheral veins?

A

15%

avoids phlebitis and osmolarity

35
Q

What is the ideal concentration of glucose?

A

9-20% approx.

36
Q

How does the pH of glucose change over time?

A

pH drops as solutions age from pH 6 to 3.

37
Q

What are the stages of lipid instability?

A
  1. aggregation
  2. creaming- reversible on agitation. Pale white layer forms at the top of the bag
  3. cracking - irreversible and dangerous
38
Q

De-stabilised lipids have the potential for harm via what?

A

Hepatic uptake reticulo-endothelial system
Uptake into heart, lung and liver
Lipid micro-emboli in lung/capillary occlusion.

39
Q

What factors affect the stability of lipids?

A

Positive ions - +2 ions will have more affect than +1 ions. Electrostatic effect causes repulsion.
pH - ideal pH 8. Below pH 6 ppt.
Glucose conc - not over 20% as lowers the pH
Time - emulsions destabilise over time
Lipid emulsion dilution as conc. decreases stability

40
Q

What is the ideal pH of PN bag to ensure lipid stability?

A

pH 8 and (pH below 6 to avoid ppt)

41
Q

What is the impact of amino acids in TPN?

A

amino acids chelate with cations
amino acids buffer TPN - stabilise
Low pH can cause ppt.

42
Q

What types of PN containers are available?

A

PVC
EVA
Multilayer

43
Q

Outline the structure of multi-layer plastic

A 
Outer layer - EVA
Intermediate layer
Barrier layer 
Intermediate layer
Inner layer EVA
44
Q

Why is PVC not a suitable plastic bag container?

A

Causes leaching of plasticersers
Extraction of DEHP which can cause patient harm (associated with male fertility issues)
Poor barrier to oxygen and moisture loss (leads to solution becoming more concentrated)

45
Q

What are the advantages of EVA as a PN bag?

A

Compatible as no leaching of placticisers

46
Q

What are the disadvantages of EVA as a PN bag container?

A

Not ideal as poor oxygen barrier –> oxidation reactons

47
Q

Why are multi-layer bags the ideal choice?

A

100x better barrier to oxygen

Reduces oxidation reactions and loss of ingredients

48
Q

What is the problem with folic acid in a PN bag?

A

Can bind to plastics so will never reach the patient

49
Q

How can PN feeds be protected from light?

A

Use a light protective cover

Amber syringes and IV lines are available

50
Q

What considerations should be made regardign home parental patients (HPN) and vitamin C?

A

Add additional vitamin C to the PN feed, to allow for known losses in the first 24 hours

51
Q

What temperature should PN feeds be stored at?

A

in fridge at 2-8’c

52
Q

What should be done to the PN bag before administration?

A

Allow the PN feed to warm up to room temperature for one hour before use. Cold infusions can cause cardiac arrest.

53
Q

What is the EM2400 compounder?

A

Barcodes confirm ingredient iD. Fixed order of addition

Automated volume addition

54
Q

What QC testing should be carried out on PN bags?

A

Electrolyte - flame photometer, atomic absorption, ICP-OES chromatography as inductively coupled plasma optical emission spectrometry.
Refractive index - confirms the correct soureces of macroingredients particular glucose. Ingredients have different indicies.

PA30304 (11 decks)

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