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Indications for parenteral nutrition (PN)

Discuss the indications of PN?

  • Inadequate or unsafe oral and/or enteral nutritional intake
  • A non-functional, inaccessible or perforated (leaking) gastrointestinal tract.

So enteral feeding is contraindicated in diffuse peritonitis, intestinal obstruction, intractable vomiting, paralytic ileus, intractable diarrhoea and gastrointestinal ischaemia.

How many days would you wait before initiating PN?

In many studies of the use of PN, the majority of patients are able to eat orally within 6-8 days; it is unlikely that these patients benefit from such short-duration PN. This is likely to be true even in malnourished patients. So based on these data, PN is often recommended if enteral intake has been, or is anticipated to be inadequate for 7-10 days.

NICE 2006 – There is no minimum length of time for the duration of parenteral nutrition.

How would you deliver PN?

  • Continuous administration of parenteral nutrition should be offered as the preferred method of infusion in severely ill people who require parenteral nutrition.
  • A gradual change from continuous to cyclical delivery (12-14 hrs) should be considered in patients requiring parenteral nutrition for more than 2 weeks.  Cyclic infusion is used with a tapering-up period at the beginning and a tapering-down period at the end to avoid hyper-/hypoglycemia.

Discuss the protocol for laboratory monitoring of nutrition support?
NICE 2006
Monitoring of patients’ tolerance to parenteral nutrition includes careful measurements of fluid intake and output, and selected laboratory studies.

  • Baseline- FBC, U&ES, LFTs including albumin and INR, CRP, Glucose, B12, Folate, ferritin, Mg, PO4, Ca, Zn, copper, selenium.
  • Frequency of monitoring
    • Daily until stable- U&ES (then 1-2 weekly), Glucose (twice daily, till stable then weekly) Mg, Po4 (daily if risk of refeeding, 3/weekly otherwise till stable, then weekly)
    • Weekly- LFTs (twice weekly till stable), Ca, albumin, CRP (2-3/week till stable), FBC
    • 2-4 weekly depending on results- Zn, Cu, folate, B12,
    • 3-6 monthly- Ferritin, Manganese (if on home TPN)
    • 6 monthly- 25 OH Vit D if on long term support.

What is the composition of PN solution?
The initial composition of the parenteral nutrition solution should be determined by a patient’s tolerance to:

  • Parenteral glucose (patients with diabetes or critical illness are susceptible to hyperglycemia)
  • Amino acids (renal or hepatic disease may cause intolerance to protein loads)
  • Fats (eg, critical illness or sepsis may result in hypertriglyceridemia)

Initial infusion rates of these macronutrients generally begin at 2 to 4 mg/kg/min of CHO in adults, 0.5-1.0 g of protein/kg/day, and 1.0 g of lipid/kg/day.
Electrolytes, minerals, trace elements and a multivitamin preparation are generally added to the parenteral solution.
For details see the chapter on Calorie requirements.

What are the routes of administration of PN?

  • Peripheral PN- PN may be safely used by a peripheral access (short cannula or midline catheter), using a solution with low osmolarity, when a significant portion of the non-protein calories are given as lipids. Midline catheters are a preferable option when peripheral i.v. therapy is expected for more than 6 days.
  • Central PN- Central venous accesses (i.e. venous devices whose tip is centrally placed) can be classified as short term and long term accesses. Long term (> 3 months) home parenteral nutrition (HPN) requires a long term venous access device, such as a tunneled central catheter (Hickman, Broviac, Groshong, etc.) or a totally implanted port. PICC or a centrally inserted CVC can be used for short or medium term use. PICCs catheters can be used for prolonged PN (up to 3-6 months) both in hospitalized patients and for home TPN.
  • PICC is a central line placed via peripheral vasculature. Midline is a shorter version of the PICC. It is inserted in the same fashion, but it terminates in the axillary veins rather than in the central circulation. Midline catheters can b used for  up to 2 weeks.

Which is the most appropriate position of the tip of a central venous access for parenteral nutrition?

Central PN (i.e. high osmolarity PN) should be delivered through a catheter whose tip is positioned in the lower third of the superior vena cava, or at the atrio-caval junction, or in the upper portion of the right atrium. This is associated with the least incidence of mechanical and thrombotic complications.

Ref

  1. NICE guidance: Nutrition support in adults

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