CI: Best Method to Estimate RMR (2010)

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To compare measured REE using indirect calorimetry with the thermodilution technique for measuring cardiac output and calculating REE using the Fick equation in a critically ill population. 

Inclusion Criteria:

Consecutive patients with an indwelling Swan-Ganz catheter in the surgical ICU. Hemodynamically stable and mechanically ventilated.

Exclusion Criteria:

No significant tracheostomy leaks and FiO2<60%.

Description of Study Protocol:


Consecutive patients


Cross-Sectional Study

Blinding used

Not applicable


REE measured using indirect calorimetry and the thermodilution method

Statistical Analysis

Limits of agreement analysis as described by Bland was used to assess the agreement between the indirect calorimetry and thermodilution method. For comparison with other studies, Pearson's correlation coefficient was calculated. Probability values<0.05 were considered statistically significant. An error of 5% (approximately ±100kcal per day) between the two methods was deemed acceptable for clinical use.

Data Collection Summary:

Timing of Measurements

REE determined by both techniques within a two-hour period

Dependent Variable

Estimated energy expenditure

Independent Variables

  • REE measured by indirect calorimetry using Delta Trac 100 metabolic monitor, performed by CNSD, calibrated before each study, contained at least 20 minutes of steady-state data and were subjected to specific quality control measures to evaluate accuracy (ensuring that the SD of the REE, oxygen consumption or minute ventilation did not exceed 10% of the mean value, RQ values in physiologic range of 0.67 to 1.3)
  • REE measured by the thermodilution method, performed by ICU registered nurse, measured with Vigilant continuous cardiac output monitor.


Description of Actual Data Sample:
  • Initial N: 40 patients
    •  14 women
    • 26 men
  • Attrition (final N): 40 patients 
    • Seven had received solid organ transplants
    • Six were victims of traumatic injury
    • The remaining subjects had received general, vascular or cardiothoracic surgery 
    • Five had septic complications
  • Age: Range 16-87 years
  • Ethnicity: Not mentioned
  • Other relevant demographics:
  • Anthropometrics:
  • Location: Texas.


Summary of Results:

Other Findings

  • Mean values for REE were 1,928±558 vs. 1,898±518kcal per day for the indirect calorimetry and thermodilution methods, respectively and were not significantly different
  • There was a significant correlation between the REE (r=0.56, R2=0.31, P<0.001)
  • To show agreement between the two methods, all data points must fall between solid lines at ±100kcal, and since many data points lie outside the limits, poor agreement is shown between the two methods (P<0.0005)
  • However, there was great variation between the two techniques for the majority of patients such that REE determinations did not agree (t=6.8, P<0.005)
  • In 70% of the patients, REE determinations differed by>20% and in 10% of the patients by 50%
  • Additionally, the greater the difference between the two methods, the more the thermodilution method tended to overestimate REE.  
Author Conclusion:

In conclusion, we emphasize that two methods of measuring REE, indirect calorimetry and thermodilution method, cannot be said to agree or disagree on the basis of correlation or similar means. Our data show that, when appropriately analyzed, thermodilution method does not agree with indirect calorimetry for measuring REE in critically ill patients, and therefore, we conclude that the clinical utility of the thermodilution method for estimating REE is poor. Because indirect calorimetry generally is accepted to be the gold standard for bedside determination of REE, we recommend that it should be used for estimation of energy requirements in critically ill patients whenever possible. 

Funding Source:
Government: Lackland AFB
Reviewer Comments:
  • Large sample size
  • Valid IC protocol 
  • Well done statistical analysis.
Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
3. Were study groups comparable? N/A
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? N/A
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) N/A
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? N/A
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? Yes
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? N/A
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) N/A
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  6.6. Were extra or unplanned treatments described? Yes
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? N/A
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes