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

Hyperglycemia

Hyperlipidemia

Hypercarbia
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

Discussion

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

References

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).

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