Pvii / 21A04: Outline the dose (10% marks), composition (60% marks) and side effects (30% marks) of total parenteral nutrition (TPN)

21A04: Exam Report

Outline the dose (10% marks), composition (60% marks) and side effects (30% marks) of total parenteral nutrition (TPN)

59% of candidates passed this question.

The pharmacology of enteral and parenteral nutrition is a level 1 topic in the first part syllabus.

The TPN dose in terms of daily calorie and other nutritional requirements were key expectations in first part of the question. A detailed list of all macro and micronutrients was required under TPN composition. Expected information about macronutrients were their forms in the TPN solution (e.g., carbohydrate in the form of glucose, protein in the form amino acids), their relative calorie contributions and their essential components (e.g., the names of the essential amino acids).

Identification of potential variability in composition and dose based on specific patient factors scored extra marks. Side effects included metabolic derangements (refeeding syndrome, over or under-feeding, hyperglycaemia, hyperlipemia), biochemical disturbances (fluid and electrolyte imbalances), organ injury (liver, pancreas) and vascular access related complications.

Limited breadth and depth of information as well as incorrect facts were prevalent in the answers that scored lower marks.

Pvii / 21A04: Outline the dose (10% marks), composition (60% marks) and side effects (30% marks) of total parenteral nutrition (TPN)

Definitions

Total parental nutrition is the complete provision of nutrition intravenously, bypassing the GI tract. Only used if unable to utilise enteral route.

Dose

  • Empiric = 25 kcal/kg/day of ideal body weight
    • protein: 1.5g/kg/day
    • carbohydrate: 4g/kg/day
    • lipids: 1g/kg/day
    • H2O: 30mL/kg/day + other losses
  • Predictive equation e.g. Harris-Benedict
    • multiply this by a stress factor to allow for effects of disease
      • g. burns / trauma patient increased requirement
  • Indirect calorimetry

Composition

  • Variable formulations available depending on specific circumstance, e .g. in obesity: high protein, hypocaloric nutrition preferred in (esp BMI >40)
  • For standard 3 in 1 PN:-
    • 2-2.5L bag, foil packaged to protect from UV
    • Energy 900 – 1200kcal/L
      • 30%-50%

Macro

  • Glucose 100 – 175g/L
    • as 18-50% dextrose
  • Protein 35 – 50g/L
    • as 6-14% amino acid solution
    • Must contain all 9 essential amino acids (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine)
  • Lipid 25 – 50g/L
    • as 10-30% intralipid emulsion from soybean oil / olive oil

Electrolytes

  • Na+ 30 – 40 mmol/L
  • K+ 25 – 35 mmol/L
  • Mg 2.5 – 5 mmol/L
  • PO4- 7.5 – 20 mmol/L

Trace elements

Vitamins and trace elements should be added in usual daily requirements unless specific deficiencies are known

Minerals

  • Required
    • Chromium (10-20mg/day)
    • Copper (0.3-1.5mg/day)
    • Iodine (0-1μmol/day)
    • Manganese (60- 100μg/day)
    • Selenium (20-80 μg/day)
    • Zinc (2.5 – 6.4mg/day)
  • Only if deficient
    • Iron ((1mg/day)
    • Molybdenum (20-200mg/d if suspected deficiency)

Vitamins

  • Fat soluble
    • A 1000mmols
    • D 5mmols
    • E 10mg
    • K 0-1mg
  • Water soluble
    • C 100mg
    • Thiamine 3mg
    • Riboflavin 3.6mg
    • Pyridoxine 4mg
    • Niacin 40mg
    • B12 5mg
    • Pantothenic acid 15mg
    • Biotin 60mg
    • Folic acid 400mg

Side effects

GI

    • Abnormal LFTs
    • Trace elemental deficiency
      • Copper: anaemia, neutropenia
      • Iodine: hypothyroidism
      • Chromium: glucose intolerance
      • Zinc: mental apathy, diarrhoea, rash
      • Selenium: cardiomyopathy

Metabolic

  • Hyperglycaemia
  • Hypercholesterolaemia
  • Refeeding syndrome (Po43-, K+, Mg2+)

Sepsis

  • Catheter related sepsis

Other

  • Catheter occlusion
  • Requires dedicated lumen; most PN requires CVC (associated side effects)

References

Author: Freddie Hopkinson