Question 14

Discuss the approach to nutrition of the critically ill patient under the following headings: timing of initiation, route of nutrition, estimation of calorie requirements, and the requirements for macro and micronutrients.
(100% marks)

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College answer

Aim: To allow the candidate to demonstrate knowledge of the provision of nutrition in the ICU.
Key sources include: This is a topic whose elements are repeated many times in case history format (2001.2 Q9, Discussions on timing (2022.2 Q9, 2019.2 Q9) estimation of caloric requirements (2015.1 Q7, 2007.2 Q28). CanMEDS Medical Expert.
Discussion: Given the frequency of this subject in the examination and in clinical practice a detailed and specific answer was required. These candidates who provided this did well. The most common reason for failure of this question were generic superficial statements and answers betraying a lack of knowledge or potentially poor time management.
The better answers included:

  • Statements around timing including supportive evidence and patient prior nutritional status or caloric requirements (for example burns, trauma or already malnourished, relevant surgical issues).
  • Routes of initiation included a discussion around appropriateness and patient selection of TPN vs enteral.
  • An estimation of caloric requirements included a mention of equations (for example Harris Benedict amongst others). Expert answers included mention of hypocaloric feeding and energy dense vs routine feeds.
  • Macro and micronutrients, a list of common deficient states to replace/maintain and rationale for same.


There are numerous nutrition questions in the CICM exams and the college question references only a few. To reproduce them all here would be a wasteful exercise (the interested reader is invited to just look at the list of them here). This one, however, seems to be the best so far, as it brings together all the main points into a broad "how would you feed your patients" sort of question.

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


The reader invited to look at this list of trials and guidelines from the trials and guidelines page, as this was felt to be more useful than scrolling through a towering pillar of references.

Nutrition guidelines

ASPEN guidelines 

ESPEN guidelines

Candian Critical Care Society guidelines

A comparison of them all, from 2019 (thanks, Kopp Luigi et al)

Nutrition trials

ANZICS - 2008 - lol, all these guidelines, how much difference does it make if we follow them? n=1118, Australia and NZ. No difference in anything, even though nutrition goals were reached earlier if the guidelines were followed.

TICACOS - 2011 - Indirect calorimetry instead of giving everyone 25kcal/day? n=112, in Israel. Mortality improved (32.3% vs 47.7%) but LOS increased (17.2 vs 11.7 days). 

EPaNIC - 2011 - early (d2) vs late (d8) TPN. n=4640, in Europe. No difference in mortality; but late TPN had less TPN-related complications (obvs). However: complete mess (39% of patients had an ICU LOS of less than 3 days, so, seriously...)

EDEN - 2012 - what if trophic feeding, but in ARDS? n=1000, in the US. No difference of any sort (mortality and ventilator free days were the same). 

ENTERIC - 2012 - but what if nasojejunal feeding? n=181, Australia and NZ. No difference in basically any of the outcomes, including nutrient delivery. 

EPN - 2013 - what if TPN right away, and then stop it when EN is established? n=1372, Australia and NZ. No difference in mortality, trivial difference in duration of ventilation (7.7 vs 7.2 days, literally 12 hours)

SPN - 2013 - what if both PN and EN to achieve goals? n=305 in Switzerland. Fewer infections (27% vs 38%) in the group that reached goals earlier.

CALORIES - 2014 - PN vs EN - mortality difference? n=2400, in UK. No, there was no mortality difference, or any other difference for that matter.

PermiT - 2015  - maybe only 40-50% of goal is enough? n=894, in Saudi and Canada. No difference in any outcomes. Notably: protein dose was 100%.

EAT-ICU - 2017 - what if goals achieved on Day 1 with PN+EN? n=203, doesn't matter where, no difference of any sort.

TARGET - 2018 - moar calories? 1.5cal vs 1.0cal? n=3914; Australia and NZ. No difference in any primary or secondary outcomes. 

EFFORT Protein - 2023 - moar protein? 1.2 vs 2.2g/kg, n=1329 all over the world. No benefit and perhaps evidence of harm in AKI and more severe illness.