Parenteral Nutrition Flashcards
What is the primary goal of PN?
- 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
What is PN?
an infusion of a stable mixture of nearly ‘all’ nutrients
- it is a chemical soup
What does a TPN infusion normally contain?
- Protein
- Carbohydrates
- Fat
- Electrolytes
- Trace elements
- Vitamins
- Water
50+ components mixed together in a single bag
PN Presentations: What is a ‘Triple chamber bag’?
Separate glucose, amino acid & lipid
PN Presentations: What is a ‘2 in 1’ bag?
Aqueous ingredients only (separate from lipid)
PN Presentations: What is a ‘3 in 1’ bag?
All ingredients in one bag (aqueous & lipid)
PN Presentations: What is a ‘Lipid’ bag?
Fat/lipid based ingredients (separate from aqueous)
PN Presentations: What is a ‘1 in 1’ bag?
Amino acid and electrolyte replacement
What is the role of the Pharmacist as part of the Nutritional Support Team?
- 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
What are the main factors influencing PN formulations?
Stability & compatibility are infuenced by several factors:
- Ingredients
- Preparation & Compounding
- Containers
- Storage
How can sunlight affect the chemical stability of PN formulations?
Breakdown of Vitamin A when exposed to sunlight
How can entrained air affect the chemical stability of PN formulations?
Formation of lipid peroxides - When exposed to oxygen and sunlight Oxidation of amino-acids Breakdown of vitamins - When exposed to oxygen and trace elements
Describe the oxidation of Vitamin C
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
The oxidation of Ascorbic acid (Vitamin C) is catalysed by…
Copper ions and Light
What can be the consequence of precipitation in PN bags?
Can block small capillaries e.g. in the lungs and other organs resulting in pulmonary emboli
Calcium & Phosphate insoluble ppt:
Solubility is influenced by….
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
How does the compounding process influence PN Precipitation?
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
What is the normal dilution and order of mixing?
See separate diagram on sheet
How can the concentration of glucose affect PN bags?
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
What are the 3 main stages of lipid instability?
Aggregation Creaming - Reversible on agitation Cracking - Irreversible and dangerous!
What are the main factors affecting repulsion in a lipid emulsion?
Positive ions pH - Ideal pH 8 - Below pH 6 = ppt (bad) Time Glucose conc
How do Amino acids affect PN bags?
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.)
Container types: PVC
Not suitable as leaching of plasticisers
- Extraction of DEHP which can cause patient harm
Poor barrier to oxygen and moisture loss
Container types: EVA
Not ideal as poor oxygen barrier
Compatible - No leaching of plasticisers
