The document discusses several methods to estimate total energy expenditure in critically ill patients, including empiric/simplistic methods based on weight or surface area, predictive equations, indirect calorimetry, and the Fick method. It notes the advantages and limitations of each method. It then provides recommendations for nutritional goals for critically ill patients, including prescribed total parenteral nutrition for a sample patient with multiple bowel perforations and a small bowel resection.

1. Nutritional requirement in
Critically ill
Dr SANTOSH KUMAR BHASKAR

2. QUESTION
• A 26-year-old female is admitted to the ICU post
operatively with faecal peritonitis as a result of
multiple bowel perforations secondary to Crohn’s
disease. She has had the majority of her small
bowel resected and is to be prescribed total
parenteral nutrition (TPN).
• Describe the available methods to estimate total
energy expenditure in critically ill patients and
outline their advantages and limitations.?

3. Empiric/Simplistic:
• This may be based just upon weight or surface
area – Most critically ill patients will have
requirements of approx. 25 kCal/kg/day.
• Advantages – quick, simple and cheap.
Universally available
• Disadvantages – may be inaccurate

4. • Predictive equations:
• Many versions such as Harris-Benedict,
PennState, Faisy etc., based upon various
direct measurements.
• Advantages – quick, simple and cheap.
Universally available
• Disadvantages – Inaccuracy, usually
underestimate requirements. Need
for multiple correction factors.

5. • Indirect Calorimetry:
• Measures oxygen uptake and carbon dioxide
production using the assumption that all of the oxygen
uptake is used for oxidation of substrates.
• Advantages: Most accurate method. Bedside monitor
than can be integrated with ventilator.
• Disadvantages: Expensive; requires technical expertise,
limited availability. Inaccurate in the setting of high
FiO2 or PEEP, leaks in circuit, recent ventilator changes,
changes in oxygen concentration, hemodynamic
instability, temperature changes or haemodialysis.

6. • Fick method
• Determines oxygen consumption from indwelling
pulmonary artery catheter, then uses caloric value
for oxygen to calculate energy expenditure.
• Advantages: More accurate than predictive
equations, cheaper and more available than indirect
calorimtery.
• Disadvantages: Highly invasive. Does not account for
pulmonary oxygen consumption.

7. • Describe how you would prescribe her TPN ?

8. • Standard TPN delivery 2 litre bags
• If the total non-protein kCal required is 2000/day, ratio for CHO to fat is 70:30
Dextrose:
1400Kcal
824mls (412g dextrose at 50% solution at 3.4Kcal/gram and requiring 1400KCal)
Lipid:
600Kcal
Using 10% lipid (1.1kcal/ml), will need 545mls 10% lipid
Adjust if using propofol as sedation (approx. 1kcal/ml as fat)
Protein:
1.5-2g/kg/day
2 x 50 = 100 grams/day of amino acids
Using 10% solution amino acid solution (100g/L) 1 Litre of 10% amino acid solution
• Electrolyte, vitamins and trace elements are added to the solution in a standard
fashion, but may be individually tailored to the patient’s requirements.

9. Nutritional goals for the critically ill
patient

10. Nutritional goals for the critically ill
patient

11. • Whichever way one estimates the nutritional
goal, one should aim to provide at least 50-
65% of that goal dose to achieve the benefits
of enteral nutrition. This is the dose required
to get the various protective benefits, such as
the decreased risk of infection and improved
return of cognitive function in head injury.

12. Safe minimum
• LITFL reports that the daily requirement of
glucose is approximately 4-5g/kg/day in
severely catabolic patients, but the main
reference for this is Thomas Ziegler's 2008
NEJM article, which makes no specific dose
recommendation (only that 60-70% of the
total caloric goals should be met by dextrose).

13. Safe minimum
• The 2003 ESPEN guidelines recommend
2g/kg/day of glucose as the minimum amount
of carbohydrate requred. Their
recommendation is based on Bier et al (1999)
- the Report of the IDECG Working Group on
lower and upper limits of carbohydrate and fat
intake.

14. Safe minimum
• According to this report, about 50g/day of
glucose is enough to prevent ketosis in the
adult. Approximately 100g/day is oxidised
irreversibly by the brain, and therefore that
(with a 50% bonus for safety) should be the
minimal daily recommended intake. That
comes to just over 2g/kg for the average 70kg
adult.

15. Safe maximum
• It has been documented that the maximum
oxidation rate of glucose in the stressed
patient is 4–7 mg kg−1 min−1 (or 400–700 g
day−1 for a 70 kg patient). Therefore, in order
to decrease the risk of metabolic alterations,
the maximum rate of glucose infusion should
probably not exceed 5 mg kg−1 min−1. For a 70
kg patient, this would be ∼2000 kcal glucose
and this is not generally exceeded in standard
PN regimes.

16. Lipids
• Apart from glucose, fatty acids offer a source
of metabolic energy substrate, and they are
essential for the maintenance of cellular
function. Particularly, the fatty acids linoleic
acid (omega-6) and α-linoleic acid (omega-3)
cannot be synthesized in the body and are
therefore essential.

17. Lipids
• ESPEN suggest that the typical ICU patient
requires 9–12 g/day of linoleic acid and 1–3
g/day of α-linoleic acid. Other desirable fatty
acids include eicosopentanoic acid and
docosahexaenoic acid, which are available in
fish oil, and oleic acid, which is available in
olive oil.

18. Safe minimum and maximum
• Bier et al (1999) in the already quoted IDECG report have
recommended that a daily fat intake should be greater than 10% (as
this does not meet the daily requirement of essential fatty acids)
and less than 65-70% (as this would prevent the theoretical
minimum daily carbohydrate intake).
• Therefore, a middle-ground 30% was recommended as the ideal
proportion of daily fat. The mass of the daily lipid requirement is
therefore about 1g/kg/day, or 70g for a normal-sized person; a sane
range is 0.7-1.5g/kg/day.
• In the distant past, it was thought that more energy (up to 50% of
daily energy requirements) should be provided by lipids; however
these days this has been reduced to about 30%, which
should maintain a respiratory quotient in the range of 0.85-0.90.

19. Proteins
• Daily protein requirements range from 1.5-
2.0g/kg/day.
• Why not more?
• Well; the addition of extra protein beyond this
dose does not result in an increase of protein
uptake by the tissues of burns patients, and
they are generally held to be the most
protein-hungry of all ICU demographic groups

20. What is the upper limit of protein
supplementation?
• The IDECG Report mentions studies administering
4g/kg/day to experimental subjects (but no
reference is given).
• Moreover, athletes and weightlifters in training
routinely take up to 8g/kg/day with no apparent
ill effects, and one may again recall the
indigenous populations of carb-poor areas who
subsist on high-protein diets for the duration of
their lives.

21. The ideal carbohydrate:fat ratio
• Certain basic facts must be remembered about the
daily human physiological requirements.
• Carbohydrate is the preferred energy substrate of most
tissues
• Lipid is the preferred energy substrate of some (few)
tissues
• Amino acids should not be used for fuel under
conventional circumstances, but the breakdown and
synethesis of protein contributes to the overall energy
requirement. The critically ill patient is in a stressed
state and will have altered (increased) amino acid
requirements.

22. The ideal carbohydrate:fat ratio
• A carbohydrate:fat ratio of 70:30.
This is again based in the nutritional
recommendations made by IDECG. Those are
generic, and apply equally well (or badly) to
the healthy as well as the sick.

23. But
• How do you know your patient is benefiting
maximally from this ratio?
• Is there any method to determine the ideal
ratio for any given patient, and individualise
their nutrition?

24. • One such method may be indirect calorimetry. As
it offers a measurement of the respiratory
quotient, it could be the ideal means of
calculating the carbohydrate:fat ratio.
• The theoretical range for the RQ is from 0.67 to
1.30; RQ for fat is 0.70, for protein is 0.80 and for
carbohydrate is 1.00.
These values were obtained by Graham Lusk in 1924, in a famous and often-quoted paper.

26. References
• Fink's Textbook of Critical Care: Chapter 94: Critical Care
Nutrition by JUAN B. OCHOA, DAREN K. HEYLAND,
STEPHEN A. McCLAVE.
• Doig, Gordon Stuart. "Parenteral versus enteral nutrition in
the critically ill patient: additional sensitivity analysis
supports benefit of early parenteral compared to delayed
enteral nutrition." Intensive care medicine 39.5 (2013): 981-
982.
• Doig, Gordon S., et al. "Early parenteral nutrition in
critically ill patients with short-term relative
contraindications to early enteral nutrition: a randomized
controlled trial." JAmA 309.20 (2013): 2130-2138.

27. •Thanks for
patients
listening