Parenteral Nutrition

Question 1

What is the primary goal of PN?

Answer 1

• Provide adequate calories and proteins whilst maintaining fluid balance
• Prevent malnutrition and associated complications

Whilst remembering that:
- Many factors affect the amount of each component that the patient needs, each must be evaluated and assessed for its value; dose; compatibility and stability

Question 2

What is PN?

Answer 2

an infusion of a stable mixture of nearly ‘all’ nutrients

- it is a chemical soup

Question 3

What does a TPN infusion normally contain?

Answer 3

• Protein
• Carbohydrates
• Fat
• Electrolytes
• Trace elements
• Vitamins
• Water

50+ components mixed together in a single bag

Question 4

PN Presentations: What is a ‘Triple chamber bag’?

Answer 4

Separate glucose, amino acid & lipid

Question 5

PN Presentations: What is a ‘2 in 1’ bag?

Answer 5

Aqueous ingredients only (separate from lipid)

Question 6

PN Presentations: What is a ‘3 in 1’ bag?

Answer 6

All ingredients in one bag (aqueous & lipid)

Question 7

PN Presentations: What is a ‘Lipid’ bag?

Answer 7

Fat/lipid based ingredients (separate from aqueous)

Question 8

PN Presentations: What is a ‘1 in 1’ bag?

Answer 8

Amino acid and electrolyte replacement

Question 9

What is the role of the Pharmacist as part of the Nutritional Support Team?

Answer 9

• Assess patient & requirements
• Educational programs
• Co-ordination and arrangement of home therapy prescriptions
• Assess potential risks/problems, including stability and compatibility
• Formulate regimen
• Minimise hazardous reactions
• Provide, delivery safe & effective product

Question 10

What are the main factors influencing PN formulations?

Answer 10

Stability & compatibility are infuenced by several factors:

• Ingredients
• Preparation & Compounding
• Containers
• Storage

Question 11

How can sunlight affect the chemical stability of PN formulations?

Answer 11

Breakdown of Vitamin A when exposed to sunlight

Question 12

How can entrained air affect the chemical stability of PN formulations?

Answer 12

Formation of lipid peroxides
- When exposed to oxygen and sunlight
Oxidation of amino-acids
Breakdown of vitamins
- When exposed to oxygen and trace elements

Question 13

Describe the oxidation of Vitamin C

Answer 13

Ascorbic acid (Vitamin C)
- Oxidised in presence of O2 to...
Dehydro-ascorbic acid
- Converted in presence of H20 to
Diketogluconic acid
Oxalic acid
- Will ppt with Ca++ ions

Question 14

The oxidation of Ascorbic acid (Vitamin C) is catalysed by…

Answer 14

Copper ions and Light

Question 15

What can be the consequence of precipitation in PN bags?

Answer 15

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

Question 16

Calcium & Phosphate insoluble ppt:

Solubility is influenced by….

Answer 16

Salt
- Dibasic much less soluble than mono
Concentration
pH
- Salt form of calcium phosphate depends upon pH
Other ingredients
- Amino acid source & concentration, electrolyte conc (Mg), organic source of Ca or Po4

Question 17

How does the compounding process influence PN Precipitation?

Answer 17

Storage temperature (after mixing)
- ppt more likely as temp rises with the gluconate salt
Time after manufacture
Use of in-line filters
Use of organic compounds
- e.g. glycerophosphates

Question 18

What is the normal dilution and order of mixing?

Answer 18

See separate diagram on sheet

Question 19

How can the concentration of glucose affect PN bags?

Answer 19

High concs (40-50%) can:
- Destabilise fat emulsions
- Can cause hyperglycaemia
15% max concentration for peripheral veins
Viscosity enhances the stability of lipid emulsions
- Benefits seen if final conc. is in range 9-20%
pH drops as solutions age from pH 6 - pH 3

Question 20

What are the 3 main stages of lipid instability?

Answer 20

Aggregation
Creaming
- Reversible on agitation
Cracking
- Irreversible and dangerous!

Question 21

What are the main factors affecting repulsion in a lipid emulsion?

Answer 21

Positive ions
pH
- Ideal pH 8
- Below pH 6 = ppt (bad)
Time
Glucose conc

Question 22

How do Amino acids affect PN bags?

Answer 22

Chelate metal ions
Buffer TPN
- significant stabilising effect on other constituents (e.g. lipid emulsions)
Low pH may cause precipitation e.g. tyrosine
Commercial formulations vary in
- pH from 5 - 7.4
- Buffering capacity (arganine, histidine, lysine conc.)

Question 23

Container types: PVC

Answer 23

Not suitable as leaching of plasticisers
- Extraction of DEHP which can cause patient harm

Poor barrier to oxygen and moisture loss

Question 24

Container types: EVA

Answer 24

Not ideal as poor oxygen barrier

Compatible - No leaching of plasticisers

Question 25

Container types: Multilayer

Answer 25

Ideal choice

100x better barrier to oxygen

Reduces oxidation reactions and loss of ingredients
- e.g. ascorbic acid, amino acids

Question 26

Some ingredients bind to plastics e.g…..

Answer 26

Folic acid

Question 27

What are the main practice points associated with PN?

Answer 27

• Protect from light
• Remove as much air from the headspace as possible
• When lipid is infused separately
  
  • > add the vitamins to the fat emulsion bag
  • > trace elements to the amino acid/glucose bag (this keeps copper and vitamin c apart)
• Add additional Vitamin C to the PN feed (this allows for the known losses in the first 24 hours)

Question 28

Are drug additions to PN bags a good idea?

Answer 28

No

• Possible changes to the admixture
• e.g. Instability caused by heparin, lipid emulsion & calcium interacting

Question 29

What QC testing should be applied to PN bags?

Answer 29

Electrolytes - Na, K, Mg, Ca

• Flame photometer
• Atomic absorption
• Chromatography

Refractive Index
- Confirm correct sources of macro ingredients particularly glucos