Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
  1. Identify the factors that affect the measurement of resting energy expenditure and respiratory quotient from indirect calorimetry
  2. Identify the potential sources of error that may occur when performing indirect calorimetry
  3. Describe the conditions necessary to obtain optimal results when performing metabolic tests
  4. Describe the clinical effect indirect calorimetry has had in the nutritional management of critically ill patients.

Population addressed

Inclusion criteria for articles

  1. None discussed

Terminology Defined

  • “Indirect calorimetry” = Weir equation
  • Energy expenditure = (3.94 x VO2) + (1.11 x VCO2) such that 80% O2 consumption accounts for energy expenditure & 20% due to CO2 production

Weir JB, 1949

  • Steady state or metabolic equilibrium: a 5-min interval during which VO2 and VCO2 change by less than 10% or the Coefficient of variation for these two values is <5%

Feurer ID, Crosby LO, Mullen JL, 1984; Feurer ID, Mullen JL,, 1986

  • Respiratory Quotient: Ratio of VCO2/VO2; An associated physiologic range is from 0.67 – 1.3; Hence, values outside this range are generated though error and beneficially used to validate IC measurement accuracy

Branson RD, 1990

Indirect Calorimetry Assumptions

  1. IC correlates best to REE (10% + Basal energy expenditure)
  2. IC is 0-3% below total energy expenditure (TEE)
  3. REE=70-90% TEE; remainder r/t diet-induced thermogenesis, physical activity
  4. Variation in REE from day-to-day
Owen, 1988; Elwyn DH, Kinney JM, Askanazi J, 1981
Inclusion Criteria:
Criteria for article inclusion
Exclusion Criteria:
Criteria for article exclusion
Description of Study Protocol:

No search procedures and sorting criteria mentioned.

Data Collection Summary:

Outcome(s) and other measures

  • Why type of information was abstracted from articles? 
  • How was it combined?
  • What analytic methods were used, if any?
Description of Actual Data Sample:

83 included in publication

  • The number of articles identified in searching process not stated.
  • 5/83 (6%) citations by primary author
  • 9 Narrative reviews; 6 textbook citations; 3 abstracts;
  • Sample size of studies ranged from n=3 healthy adults (Damask MC, Askanazi J et al, 1983 to n=164 mechanically ventilated pt on ventilator support (Swinamer DL, Grace MG, Hamilton SM 1990).
  • Characteristics of the study participants included critically-ill, clinically stable, organ failure, spinal cord injury, pts with burns, inflammatory bowel disease and obese patients.
Summary of Results:

What are the main results of the review?


  1. The REE accounts for 75% to 90% of the total energy expenditure, the remainder of which is accounted for by thermogenesis resulting from nutrient intake (diet-induced thermogenesis), environment (shivering/non-shivering thermogenesis), and physical activity

(Foster, 1987 in 100 critically ill pts; Feurer & Mullen, 1986 narrative review; Elwyn DH et al, 1981)

  1. Exposure to a cool environment and hypothermia cause increase in energy expenditure through shivering and non-shivering thermogenesis.
  2. Shivering thermogenesis is the immediate response to cold exposure and involves increased muscle work mediated by hypothalamic control.  Although the heat produced is close to the body surface, is associated with a rapid rate of heat loss, and thus, is very inefficient.

(Elwyn DH, KinneyJM, Askanazi J, 1981; Feurer & Mullen, 1986 Narrative review)

  1. Postoperative patients, hypothermic from long surgical procedures in cool operating room suites demonstrated changes in non-shivering and shivering thermogenesis.  In shivering thermogenesis, oxygen consumption increased 90%; in non-shivering thermogenesis, REE increase was avoided.

(Rodriguez, 1983)

[All other un-related topics to this particular evidence analysis question in the narrative review were not completed]

Abstract results including quantitative data and statistics, especially effect sizes, are not reported.

Author Conclusion:

“Indirect calorimetry has proved to be a valuable research tool over the past two decades and has shaped a number of the clinical physiologic principles involved in nutrient substrate assimilation and the stress-induced metabolic response.

Unfortunately the impact of indirect calorimetry in patient care is limited by the fluctuations in the clinical condition of critically ill patients and the difficulties in the delivery of prescribed nutritional regimens.  The potential for improving th usage of indirect calorimetry at a particular institution lies in developing strict protocols for performing metabolic testing, paying meticulous attention to accuracy and avoiding error, and forming a multidisciplinary team to interpret and implement test results.”
Funding Source:
University/Hospital: University of Louisville School of Medicine, Veterans Affairs Medical Center
Reviewer Comments:


  • Comprehensive review of literature citations.


  • Most recent study cited was in 1991; therefore, missing 12 years of more recent literature
Quality Criteria Checklist: Review Articles
Relevance Questions
  1. Will the answer if true, have a direct bearing on the health of patients? Yes
  2. Is the outcome or topic something that patients/clients/population groups would care about? Yes
  3. Is the problem addressed in the review one that is relevant to dietetics practice? Yes
  4. Will the information, if true, require a change in practice? Yes
Validity Questions
  1. Was the question for the review clearly focused and appropriate? Yes
  2. Was the search strategy used to locate relevant studies comprehensive? Were the databases searched and the search termsused described? No
  3. Were explicit methods used to select studies to include in the review? Were inclusion/exclusion criteria specified andappropriate? Wereselectionmethods unbiased? No
  4. Was there an appraisal of the quality and validity of studies included in the review? Were appraisal methodsspecified,appropriate, andreproducible? No
  5. Were specific treatments/interventions/exposures described? Were treatments similar enough to be combined? Yes
  6. Was the outcome of interest clearly indicated? Were other potential harms and benefits considered? Yes
  7. Were processes for data abstraction, synthesis, and analysis described? Were they applied consistently acrossstudies and groups? Was thereappropriate use of qualitative and/or quantitative synthesis? Was variation in findings among studies analyzed? Were heterogeneity issued considered? If data from studies were aggregated for meta-analysis, was the procedure described? No
  8. Are the results clearly presented in narrative and/or quantitative terms? If summary statistics are used, are levels ofsignificance and/or confidence intervals included? Yes
  9. Are conclusions supported by results with biases and limitations taken into consideration? Are limitations ofthe review identified anddiscussed? No
  10. Was bias due to the review's funding or sponsorship unlikely? Yes