Question 28

With regards to nutrition in the critically ill patient

a) list the methods available to estimate energy expenditure in the critically ill patient

b) list the metabolic and clinical problems associated with overfeeding

c) list the clinical and biochemical features of the  refeeding syndrome ?

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College Answer

a) list the methods available to estimate energy expenditure in the critically ill patient

Indirect calorimetry
Fick principle ( in patients with a PAFC)

Predictive equations

b) list the metabolic and clinical problems associated with overfeeding

Hepatic steatosis



Hyperosmolarity and hypertonic dehydration (in patients fed excess nitrogen who have impaired urine concentrating ability)
Azotemia (due to excess nitrogen intake)

c) list the clinical and biochemical features of the  refeeding syndrome ?

-seen when normal intake is resumed after a period of initial starvation
- Low PO4, Mg and K and thiamine deficiency
- Can presents with weakness, arrythmias and cardio-respiratory failure


The article linked below compares all three methods mentioned in the college answer. Specifically, for each mentioned topic the following rambling digressions are available:

In brief:

A Comparison of Methods
to Estimate Metabolic Energy Requirements
in Critical Illness
Method Physiology Advantages Limitations
Predictive  Equations
  • Calculation of metabolic requirements made on the basis of empirical experimental data
  • Typically, input information is gender, height, age and weight
  • Specific metabolic abnormalities (eg. burns or sepsis) can be factored in as multipliers
  • Range from complex equations to simple (25cal×kg per day) formulae
  • Cheap
  • Quick
  • Requires no expertise
  • Accurate for many circumstances, particularly straightfrward ICU patients
  • Predict requirements, i.e. useful goals of management
  • Tend to be inaccurate
  • The sicker the patient, the less accurate the predictions
Reverse Fick method
  • Determines oxygen consumption from pulmonary artery catheter:
  • Oxygen utilisation in metabolic processes is correlated to the metabolic rate.
  • Knowing the cardiac output, one can calculate the oxygen consumption of the organism from the arteriovenous oxygen content difference.
  • Accurate - more so than predictive equations
  • Reproduceable
  • Cheaper than the metabolic cart, and more widely available
  • Invasive
  • Does not incorprate the metabolic requirements of the lungs
  • Inaccurate in severe pulmonary pathology, eg. ARDS
Indirect calorimetry
  • Oxygen uptake and CO2 production are monitored by a specialized module attached to the ventilator
  • From the consumption of oxygen, one can estimate the metabolic rate (assuming all oxygen is used to oxidise substrate)
  • The most accurate method of determining energy use
  • Module can integrate with the ventilator

Indications may include:

  • Extremes of obesity
  • Extremes of core body temperature (eg. in hypothermia)
  • Extremes of age
  • Very expensive
  • It makes the assumpation that all oxygen use is for oxidation of substrate
  • It is a complex procedure and it requires special equipment
  • It is a measure of metabolic fuel consumption, not demand.
  • It is not associated with any clinical benefit.
  • Inaccurate at high PEEP
  • Inaccurate with high FiO2
  • Invalid in the presence of circuit leak
  • Difficult to interpret if the ventilator settings keep changing rapidly

The complications of overfeeding the critically ill patient are discussed elsewhere.

In brief, they are as follows:

  • Hyperglycaemia
    • Thus, risk of hyperosmolar non-ketotic hyperglycaemia
  • Uraemia
    • Thus, risk of urea-induced hypertonic dehydration
  • Hyperlipidaemia
  • Fatty liver disease
  • Hypercapnea

Refeeding syndrome is also discussed elsewhere, but - in brief point form - its features are as follows:

  • Hypokalemia
  • Hypophosphatemia
  • Hyponatremia
  • Hypomagnesemia
  • Onset following the reintroduction of food after a prolonged starvation
  • Clinical features are most closely related to the magnitude of the electrolyte derangement


Flancbaum, Louis, et al. "Comparison of indirect calorimetry, the Fick method, and prediction equations in estimating the energy requirements of critically ill patients." The American journal of clinical nutrition 69.3 (1999): 461-466.


Klein, Catherine J., Gena S. Stanek, and CHARLES E. WILES III. "Overfeeding macronutrients to critically ill adults: metabolic complications." Journal of the American Dietetic Association 98.7 (1998): 795-806.


Hearing, Stephen D. "Refeeding syndrome." BMJ 328.7445 (2004): 908-909.


Stanga, Z., et al. "Nutrition in clinical practice—the refeeding syndrome: illustrative cases and guidelines for prevention and treatment." European journal of clinical nutrition 62.6 (2008): 687-694.


Kraft, Michael D., Imad F. Btaiche, and Gordon S. Sacks. "Review of the refeeding syndrome." Nutrition in Clinical Practice 20.6 (2005): 625-633.


Khan, Laeeq UR, et al. "Refeeding syndrome: a literature review."Gastroenterology research and practice 2011 (2010).