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CI: Best Method to Estimate RMR (2010)

Citation:

Flancbaum L, Choban PS, Sambucco S, Verducci J, Burge JC.  Comparison of indirect calorimetry, the Fick method, and prediction equations in estimating the energy requirements of critically ill patients.  Am J Clin Nutr 1999; 69(3):461-6. 

PubMed ID: 10075331
 
Study Design:
Cross-Sectional Study
Class:
D - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To compare REE measured by indirect calorimetry with REE calculated by using the Fick method and prediction equations by Harris-Benedict, Ireton-Jones, Fusco and Frankenfield.
Inclusion Criteria:
All patients were mechanically ventilated, were receiving TPN, and already had an oximetric pulmonary artery catheter in place for the purpose of enhancing clinical care at the time of the evaluation.
Exclusion Criteria:
None specifically mentioned.
Description of Study Protocol:

Recruitment

Patients admitted to the surgical ICU of The Ohio State University Hospital.

Design

Cross-Sectional Study.

Blinding used (if applicable)

Not applicable.

Intervention (if applicable)

RMR measured by indirect calorimetry and estimated using equations.

Statistical Analysis

Data were first analyzed by repeated measures ANOVA based on the null hypothesis.  Differences between measures were evaluated by determining 95% CIs for the difference in means between the methods and the standard (indirect calorimetry) using standard paired t tests and the Bonferroni inequality.  The relative ordering of the methods was determined by calculating correlation coefficients and the mean absolute differences were determined.

Data Collection Summary:

Timing of Measurements

Prospective trial of indirect calorimetry and information for equations.

Dependent Variables

  • RMR measured using indirect calorimetry using a MedGraphics Critical Care Monitor for > 15 minutes, test discontinued if patient did not reach steady state by 5 minutes into the test, device calibrated before each use, no patients had an inspired oxygen concentration > 0.5 
  • RMR calculated using Harris-Benedict equation, no adjustments 
  • RMR calculated using Ireton-Jones equation
  • RMR calculated using Fusco equation
  • RMR calculated using Frankenfield equation for 19 subjects
  • RMR calculated using the Fick method, using a venous oxygen saturation cardiac output computer, calculated from a mean of 2 sets of hemodynamic measurements taken during the metabolic testing period with an oximetric pulmonary artery catheter 

Independent Variables

  •  Mechanically ventilated, all receiving TPN

Control Variables

 

Description of Actual Data Sample:

Initial N: 36 patients, 12 men, 24 women

Attrition (final N):  36 patients

Age:  mean age 59 +/- 22 years

Ethnicity:  not mentioned

Other relevant demographics: mean APACHE II score 22 +/- 8

Anthropometrics:

Location:  Ohio

 

Summary of Results:

 

  Energy Expenditure (kJ/day) Energy Expenditure (kcal/day) Correlation Mean Absolute Difference Underestimation
Indirect Calorimetry 8381 +/- 1940 2005 +/- 464      
Fick 6253 +/- 2466 1496 +/- 590 0.31 680 83%

Harris-Benedict

6429 +/- 1329

1538 +/- 318 0.24

528

89%

Ireton-Jones 9012 +/- 1388 2156 +/- 332 0.26 386 89%
Fusco 7465 +/- 1363 1786 +/- 326 0.26 406 89%

Frankenfield

9815 +/- 2621

2348 +/- 627 0.39

528

37%

Other Findings

Mean differences in REE calculated by using 3 methods significantly underestimated the average REE by indirect calorimetry, ranging from 915 kJ/day (219 kcal/day) for the Fusco method to 2128 kJ/day (509 kcal/day) by the Fick method.

Estimates using the Ireton-Jones and Frankenfield formulas were not significantly different from the mean REE by indirect calorimetry.

Mean REE by indirect calorimetry was 8381 +/- 1940 kJ/day and correlated poorly with the other methods tested (r2 = 0.057 - 0.154).  None of the formulas account for > 15% of the variability of indirect calorimetry among the patients.

This correlation did not improve after adjusting for changes in RQ (r2 = 0.28). 

The magnitude of typical differences based on the formulas was in the range of 1672 - 2926 kJ/day (400 -700 kcal/day), with >80% of the differences being underestimates of the REE using each of the formulas except Frankenfield.

Author Conclusion:
In this study, none of the methods evaluated correlated with indirect calorimetry in estimating daily energy requirements for nutritional support.  Although predicted energy expenditure using the Ireton-Jones and Frankenfield equations did not differ significantly from MREE, the correlation coefficients were low, r =0.26 and r = 0.39, respectively, indicating that in individual patients each was a poor predictor.  These data do not support previous findings showing a strong correlation between REE determined by the Fick method and other prediction equations and indirect calorimetry.  In critically ill patients receiving TPN, indirect calorimetry, if available, remains the most appropriate clinical tool for accurate measurement of REE.
Funding Source:
University/Hospital: Ohio State University
Reviewer Comments:
Valid IC protocol.  All patients on TPN.
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? N/A
  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? N/A
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? N/A
  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? N/A
  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)? Yes
  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