College Answer

Central venous access;

Mixture of Protein, Fat and Carbohydrate, low amounts and slowly building up as tolerated;

electrolytes supplementation (especially at the start to prevent refeeding syndrome);

supplemental vitamins, trace elements;

monitoring of clinical state, electrolytes, LFTs, BSL,

Discussion

Commencement of TPN, and the calculations of daily intake requrements relevant to this topic are discussed elsewhere. The specific chapters of greatest interest are:

• Daily nutritional requirements of the critically ill patient
• Enteral nutrition vs parenteral nutrition in the critically ill
• When and how to start parenteral nutrition
• Contents and properties of the parenteral nutrition mixture

This question closely resembles Question 7 from the first paper of 2015, where TPN prescription was re-explored. Like Question 7 , this question was not about the need or indication for TPN, nor was it asking the candidates to debate the relative merits of parenteral and enteral routes of nutrition. The decision was made for the candidates: TPN is required.

In short, the approach should resemble the following:

• Assess daily metabolic requirements
  • Use predictive equations to make educated estimates
  • Measure energy expenditure with indirect calorimetry or reverse Fick equation
  • Apply coefficients to the findings to establish daily energy requirments in the context of a specific disease state, weg. whether one would need to contribute extra protein for a hypercatatbolic trauma patient, or extra lipid for a hypecapneic patient with COPD.
• Establish the indications for TPN, and confirm that commencement of TPN is the ideal step to take (given that in many circumstances, it is actually better to wait for 7-10 days without nutrition)
• Establish central access
• Supply macronutrients by infusing a mixture of fat protein and carbohydrate, according to the proportions established by abovementioned methods.
  • Carbohydrate: fat ratio: 70:30.
  • Protein is also required: 1.5-2g/kg/day
    • Fat is supplied as 10% lipid emulsion, at  1.1 kcal/ml
    • Carbohydrate is supplied as 50% dextrose, at 1.7 kcal/ml
    • Protein is supplied as 10% amino acid solution, as 100g/L
• Ensure regular contibution of trace elements, vitamins and micronutrients
• Ensure regular monitoring of the following parameters:
  • BSL: to prevent hyperglycaemia
  • EUCs to watch for uraemia and hypokalemia
  • CMPs to watch for the hypophosphataemia of refeedig syndrome
  • LFTs to observe for steatohepatitis and acalculous cholecystitis
• Ensure good thromboprophylaxis in view of prothrombotic effects of lipid emulsion
• Ensure regular monitoring of the central venous access site, in view of the increased risk of CVC-associated infection associated with TPN.