Total Parenteral Nutrition

Question 1

What is an emulsion?

Answer 1

a multi phase system where the disperse phase is distributed as discrete entities throughout another phase called the continuous phase

disperse phase = internal phase
continuous phase = external phase

Question 2

What are the main components of a typical emulsion?

Answer 2

disperse phase = internal phase

continuous phase = external phase (dispersion medium)

emulsifier - necessary for emulsion stability as it reduces the interfacial tension between phases

Question 3

What is a surfactant? What is its function?

Answer 3

surface active agents
- are amphiphillic molecules with a polar head and non-polar tail

adsorb at the interface between oil and water, thereby decreasing the surface tension
- increases stability of emulsions (keeps it as suspensions)

Question 4

What are the different types of emulsifiers?

Answer 4

anionic - in aqueous solution, they dissociate to form negatively charged anions of long-chain fatty acids

cationic - in aqueous solution, they dissociate to form positively charged anions of long-chain fatty acids

amphoteric - possesses both positively and negatively charged group depending on the pH of the system.

non-ionic - have a bulky hydrophilic head that is non-ionisable

Question 5

What are the indications for TPN?

Answer 5

patients whose GIT is not functional

undernourished patients who cannot ingest large volumes of oral feedings and are being prepared for
- surgery, radiotherapy or chemotherapy

disorders requiring complete bowel rest
- Crohn’s disease, ulcerative colitis, severe pancreatitis

paediatric GI disorders
- congenital abnormalities or prolonged diarrhoea

Question 6

What are TPN solutions composed of?

Answer 6

carbohydrates - dextrose and glucose (primary source of energy)

amino acids - essential, semi-essential and non-essential amino acids (highest source of energy)

lipids - essential fatty acids (concentrated source of calories)

Question 7

What are the characteristics of a TPN solution?

Answer 7

oil in water emulsion
- narrow pH with low osmolarity
- sterile
- non-pyrogenic
- stable
- isotonic

Question 8

What are the types of of TPN solutions?

Answer 8

solutions without lipids
- 2 in 1, aqueous solution
= contain amino acids, carbohydrates, electrolytes +/- water soluble vitamins and trace elements

solutions with lipids
- 3 in 1, all in one solution
= contain lipids, amino acids, carbohydrates, electrolytes +/- water soluble vitamins, fat soluble vitamins and trace elements

Question 9

What are the advantages and disadvantages of 2 in 1 solutions?

Answer 9

2 in 1 (aqueous solution)
- frequently used for neonates and paediatrics
- longer stability than 3 in 1 due to absence of lipids = 21 days

• risk of sepsis is higher than 3 in 1 due to extra line needed for lipids

Question 10

What are the advantages and disadvantages of 3 in 1 solutions?

Answer 10

3 in 1 (all in one solution)
- less administration time = one line to inject
- potentially reduced risk of sepsis = one line to inject

• precipitants cannot be seen due to emulsion formed by lipid inclusion = milky colour
• short expiration date = lipid layer will separate (7 days)
• phase separate

Question 11

What are the challenges associated with TPN composition?

Answer 11

precipitation
chemical reaction component (will react with each other)
degradation of nutrient
emulsion stability

Question 12

How does precipitation occur in TPN solutions? What is an example and how can it be prevented?
- challenge

Answer 12

the addition of additives such as electrolytes, trace elements and vitamins to TPN solutions can lead to precipitation
- result of physical incompatibilities leading to formation of new salts of low aqueous solubility

excessive concentrations of calcium phosphate
- overcome by using organic salts such as gluconate and glycerophosphate which do not dissociate in aqueous solutions

Question 13

How does chemical reaction between components occur in TPN solutions?
- challenge

Answer 13

amino acids and glucose can interact forming Maillard reaction products
- produce brown coloured compounds

reaction rate is temperature dependent

causes sub-optimal doses

Question 14

How does nutrient degradation occur in TPN solutions? How can it be avoided?
- challenge

Answer 14

periodisation could be responsible for development of complications
- free radical oxygen species attack lipids
= cause bronchopulmonary dysplasia, retinopathy

can be avoided by administering vitamins C and E which have anti oxidative activity

Question 15

What causes emulsion/drug instability in TPN solutions?
- challenge

Answer 15

patients are likely to be given other drugs alongside TPN therapy
- some drugs are compatible but some are not

pharmaceutical interactions can include precipitation, colour change and phase separation

Question 16

Why is coalescence of lipid in TPN solutions dangerous?

Answer 16

coalescence - lipid droplets grow into large fat globules and is an irreversible process

can cause IV blockage or embolism

Question 17

How can amino acids help stabilise TPN solutions? How can they cause problems?

Answer 17

amino acids can act as a buffering agent and reduce calcium phosphate precipitation

acidic amino acids can interfere with lipid emulsion
- they lower pH values causing creaming and cracking

amino acids are susceptible to deterioration in an acidic environment

Question 18

How can carbohydrates/glucose affect TPN soltuions?

Answer 18

the higher the concentration of glucose present, the more acidic the solution is

lower glucose levels may increase the risk of calcium phosphate precipitation due to lower pH (basic) promoting their formation

Question 19

What are the four classes of emulsion instabilities?

Answer 19

flocculation and creaming (are reversible)
- flocculation is formation of loose aggregates
- creaming is upwards (lipid) or downward (aqueous) movement of dispersed phase due to density differences

coalescence and breaking (are irreversible)
- coalescence is the formation of larger droplets due to surfactant layer breakdown

miscellaneous and physical and chemical changes
phase inversion

Question 20

How can coalescence be prevented?

Answer 20

surfactant use
- reduces interfacial tension

hydrocolloid use
- is a mechanical barrier

use droplets with high charge density
- repulsion occurs

Question 21

What are the contraindications for TPN?

Answer 21

egg allergy - lecithin emulsifier has egg parts

hyperlipidaemia

coagulopathy

thrombocytopenia

Question 22

What are complications caused by TPN?

Answer 22

central venous catheter - pneumothorax, infection, arterial puncture

glucose abnormalities
- hyperglycaemia = monitor blood glucose, adjust insulin dose in TPN and give subcutaneous insulin
- hypoglycaemia - caused by suddenly discontinuing constant concentrated dextrose infusion

hepatic complications
- liver dysfunction, painful hepatomegaly