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Nutrition in ICU

8. Parenteral nutrition (PN)

 

pnbag

Intravenous nutrition is required in patients who have a non-functional, inaccessible or perforated gastrointestinal tract, or who have fistulae.

Giving PN to a patient with a functioning gut confers no advantage: enteral feed should be given and prokinetics or post-pyloric feeding should be used to optimise enteral feeding as soon as possible after ICU admission. However if it becomes clear that ADEQUATE enteral feeding will not be possible or practical in such patients, guidelines now suggest that supplemental PN is started within three days of admission, particularly in malnourished patients, to avoid a large calorific deficit developing.

Access for PN may be central or peripheral: a dedicated catheter lumen is required. If a previously used lumen is used, a careful watch must be made for the development of line infection. If a patient requires a line for PN only, a single lumen line is preferred as this carries a lower infection risk.

Peripheral PN has a lower osmolality and different composition than central PN. It is given via the basilic or cephalic veins via a Peripherally Inserted Catheter (PIC) whose tip lies in the subclavian vein, or a Peripherally Inserted Central Catheter (PICC) which reaches to the SVC.

Different formulations: Electrolyte-free PN is available to give options for patients with complex needs. Different lipid emulsions available which may reduce deleterious effects on liver function in certain patients. Different calorific and protein contents are available to suit individual needs. PN with glutamine and other immunonutrients is available. Bags are usually presented in a three-chambered form to maintain stability of the ingredients. The seals between the chambers are broken before administration to the patient.

Provision of Parenteral Nutrition

Process for PN prescription:

1. Doctors decide patient needs PN
2. Dietitian calculates calorific requirements
3. Pharmacist checks the daily blood results
4. PN bag is made up aseptically in Pharmacy using a base bag with additions of electrolytes, vitamins and trace elements.
5. Composition of the bag is altered daily depending on blood results and fluid requirements

Out of hours: A protocol should be available along with some form of nutritional assessment prior to commencing feed to avoid harmful rates of feeding in patients at refeeding risk. Unaltered base bags may be used but, for reasons of stability, do not contain adequate vitamins and trace elements: additional B and C vitamins should be given in the form of Pabrinex until pharmacy reopens.

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