Summary of guidelines for nutritional support in ICU

Among the college questions, there is an entire range which all vaguely follow the pattern of "how would you feed this patient?" For example, Question 9  from the second paper of 2001 has specifically asked for strategies to manage the inadequate delivery of nutritional support in a trauma patient (who for some unspecified reason is only receiving 25% of their goal calories). In the process of constructing this summary, my main sources were the Canadian Clinical Practice GuidelinesESPEN Guidelines (2009) and the ASPEN Guidelines (2015). These are large documents, and written in an almost intentionally inaccessible manner. The time-poor candidate may be better served by the more recent summary review articles, such as the 2015 paper by Ridley Gantner and Pellegrino.

In short, the guidelines for ICU nutrition can be summarised as strongly favouring enteral nutrition, with an emphasis on earlier delivery of more calories. Protein seems to be the most important macronutrient (1.2-2.0g/kg/day). Strategies to achieve nutritional goals include protocolised feeding,  minimisation of interruptions to feeding, use of prokinetics and upright posture, returning gastric residuals under 250ml, use of post-pyloric feeding, and the supplementation of inadequate or poorly tolerated enteric nutrition with some TPN.

The most important literature on this topic has been summarised by Chris Nickson from LITFL in this excellent CCC entry. Briefly, exam candidates need to be familiar with the following landmark papers.

  • REGANE (2010): 500ml residual volumes can be tolerated without increased risk
  • EDEN (2011): 6 days of "trophic" feeding is not dangerous (no worse than full feeds)
  • TICACOS (2011): indirect calorimetry use results in better nutrition, but poorly designed.
  • EPaNIC (2011): no change in mortality (early vs late PN), but poorly designed study.
  • SIGNET (2011): glutamine is pointless, selenium may be anti-infective.
  • EPN (2013): no survival benefit from early TPN when EN is not an option for 3 days
  • SPN (2013): better nutrition (and shorter ventilation) with PN-supplemented EN
  • ENTERIC (2013): nasojejunal feeding is no better than nasogastric
  • REDOXS (2013): glutamine and antioxidants are pointless or even harmful
  • METAPLUS (2014): glutamine and antioxidants are pointless but probably not harmful
  • CALORIES (2014): no difference in mortality between early EN and early TPN
  • INTACT (2015):  higher mortality in ALI with aggressive full EN (but small trial)

The best representative SAQ that asked for a broad approach to nutrition in the critically ill was Question 14 from the first paper of 2023.  The answer is reproduced here, with links to local resources as the headings as well as landmark papers.

How much to feed?

  • Set up nutrional goals
  • Use indirect calorimetry if available; or estimate using 25kcal/kg/day
  • No single predictive equation has much of an advantage over any others

Timing of initiation

  • Start enteral nutrition within 48 hours
  • A well-nourished patient can wait 7 days without EN or TPN (CALORIES2014EPaNIC 2011)
  • A malnourished patient can't wait (immedaitely begin TPN)

Route of  nutrition

  • EN is preferred to start with (safety, price, etc) unless contraindicated
  • No mortality benefit, whether you use EN or PN
  • No major advantage to using nasojejunal feeding (ENTERIC, 2012)

Estimation of caloric requirements

  • Predictive equations, empiric formulae or indirect calorimetry can be used to estimate goals - no strong evidence that any of these is superior to the others (TICACOS, 2011)
  • Start at 30ml/hr and escalate (no strong evidence for this incremental approach)
  • Minimal "gut-protective dose" is not well established
    • 10ml/hr is safe in well-nourished patients
    • To be sure, 50-65% of goal rate is probably required
  • No strong evidence that meeting 100% energy goals improves mortality (PermiT,  2015)
  • No evidence that increased (150%) feeds improves mortality ( TARGET2018)
  • Weak evidence that this may be actually harmful in well-nourished patients
  • More likely, 100% goal rate is more appropriate in the recovery stages of critical illness
  • Earlier in the acute illness 33-66% of goal rate may be appropriate for the premorbidly well-nourished patient

Requirements for macro and micronutrients

  • Total: about 25-35 kcal/kg/day, more in severely hypercatabolic states such as thyrotoxicosis, severe sepsis, burns, multitrauma
  • Carbohydrates: 70% of total energy supply
  • Fat: 30% of total energy supply
  • Protein: 1.2g/kg/day, potentially more in burns and trauma patients - may be beneficial in the late anabolic stages of critical illness, but not in acute kidney injury or acute severe critical illness (EFFORT Protein,  2023)
  • Micronutrients and trace elements are necessary to prevent deficiency, as NG feeds and TPN may not have sufficient content, but there is no specific evidence to support an increased rate of supplementation outside of clinically significant vitamin deficiency syndromes

Management of feed intolerance

  • Minimise interuptions to enteral nutrition, and use higher make-up rates
  • Return higher gastric aspirates than you'd normally be comfortable with
  • Sit the patient up to 45º
  • Start some pro-kinetic agents (metoclopramide and erythromycin)
  • Advance the NGT into the jejunum (may not help)
  • If goals remain unmet after ~48 hours, add PN as a supplement

When and how to start TPN?

  • Start at 80% rate
  • Start pre-operatively for the malnourished surgical candidates
  • Add PN to inadequate EN to make up the lost nutrition



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