Unit 3 - Parental Nutrition 3

Question 1

What factors affect calcium phosphate precipitation?

Answer 1

Amino acids
- buffer pH changes
- forms complexes with calcium
Magnesium
- forms complexes with phosphate

Question 2

How should TPN mixtures be prepared to prevent calcium phosphate precipitation?

Answer 2

Phosphate solutions should be added to glucose solutions
- in acidic environment
Calcium solutions should be added to amino acid solutions

If not possible, phosphate solutions should be added first and calcium solutions last

Question 3

What effect can calcium phosphate precipitates cause?

Answer 3

Catheter occlusion
- raised temperature = precipitation in lines
Pulmonary deposition of calcium phosphate crystals
- respiratory distress syndrome (RDS)
- multi-organ failure (MOF)

Question 4

Which organic phosphates are used in parenteral nutrition to reduce the likelihood of preciptates?

Answer 4

Sodium glycerophosphate
Calcium glycerophosphate
Glucose-1-phosphate

Question 5

What are plasma alkaline phosphatases responsible for?

Answer 5

Cleavage of the inorganic phosphate from the organic phosphate molecule

Question 6

What is the structure of the electric double layer?

Answer 6

Cations at interface
Cations and anions in diffuse layers
Zeta potential of Intralipid = -30mV
Mutual repulsion of globules provide stability

Question 7

What three non-lipid components affect stability?

Answer 7

Glucose
- degradation products
- variations in pH
- pH effects
Amino acids
- balance of acidic and basic forms
- pH
- charge effects
Electrolytes
- dependence on valency and charge effects

Question 8

What are the advantages of parenteral nutrition drug addition?

Answer 8

Increased microbiological safety
- if addition made in pharmacy
Reduction in fluid and electrolyte load for patient
Possible cost savings
- reduction in nursing workload
- reduced delivery equipment requirements

Question 9

Why is parenteral nutrition stability important?

Answer 9

Bioavailability of drug after administration
Problems with narrow therapeutic index drugs
- anaesthetic/sedation drugs
- antibiotics
Partitioning of drugs to lipid phase
Drug stability in nutrient solution
Possible degradation products
- breakdown of hydrocortisone sodium succinate, H2 antagonists and antibiotics

Question 10

How can drugs be added to parenteral nutrition?

Answer 10

Flush technique
Multiple lumen catheters
Piggy-backing the drug via a Y-site
Direct addition to PN container
- with and without storage