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CI: Best Method to Estimate RMR (2010)


Alexander E, Susla GM, Burstein AH, Brown DT, Ognibene FP. Retrospective evaluation of commonly used equations to predict energy expenditure in mechanically ventilated, critically ill patients. Pharmacotherapy. 2004; 24(12): 1,659-1,667.

PubMed ID: 15585435
Study Design:
Cross-Sectional Study
D - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To determine which of four commonly used equations to estimate energy expenditure is precise and unbiased compared with energy expenditure as measured by indirect calorimetry.
Inclusion Criteria:
Critically ill adult patients, mechanically ventilated.
Exclusion Criteria:
  • Age under 18
  • Fraction of inspired oxygen concentration greater than 60%
  • Presence of any conditions that may affect the indirect calorimetry results, such as the presence of an endotracheal tube cuff leak or bronchopleural fistula.
Description of Study Protocol:


Evaluated all adult patients undergoing an indirect calorimetry measurement in a medical ICU in a research hospital of the National Institutes of Health Clinical Center, between March 1994 and June 2000.


Cross-sectional study.


RMR measured with indirect calorimetry and estimated using equations.

Statistical Analysis

Bias and precision of REE estimated by equations were computed using mean prediction error and root mean squared prediction error. Equations were considered precise if the 95% CI for root mean squared prediction error was within 15% of the MREE determined by IC. Equations were considered unbiased if the 95% CI interval for mean prediction error included zero. Paired T-tests were used to compared estimated REE values for each predictive equation with MEE values determined by indirect calorimetry. Data were stratified into regions of bias using classification and regression tree analysis, as well as visual inspection of estimated REE vs. MREE curves for each equation. Paired T-tests were used to compare estimated REE values with MREE values. Stepwise regression was used to evaluate the significant patient variables that might have influenced the MEE values determined by indirect calorimetry.

Data Collection Summary:

Timing of Measurements

Retrospective review of indirect calorimetry measurements and information for equations.

Dependent Variables

  • RMR measured by indirect calorimetry using the NIH Critical Care Medicine Department's Metabolic Cart Consult Service with a Delta-Trac II indirect calorimeter, by specially trained critical care respiratory therapists, in supine position, for at least 15 minutes, consisting of five one-minute samplings where oxygen consumption (maximum standard deviation of 10%), carbon dioxide production (maximum standard deviation of 6%) and RQ (maximum standard deviation of 5%) were reviewed in assessing quality, pressure and gas calibrated before each use and alcohol burn calibration every six months
  • RMR estimated using Harris-Benedict equation
  • RMR estimated using Harris-Benedict equation with activity factor of 1.2
  • RMR estimated using Ireton-Jones equation
  • RMR estimated using American College of Chest Physicians recommendation of 25kcal per kg per day based on actual body weight.

Independent Variables

  • Maintained in thermoneutral environment
  • Rested in bed or on recliner for at least 30 minutes
  • Without nursing procedures or mechanical ventilation changes for at least one hour prior to measurement
  • Age, sex, weight, height
  • Primary diagnosis, ICU diagnosis
  • APACHE III score
  • ICU day on which patients were studied with indirect calorimetry
  • Fraction of inspired oxygen
  • Presence of pneumonia
  • Concomitant drugs (sedatives, analgesics, vasoactive agents, neuromuscular blocking agents)
  • Patients evaluated in a fasting state as well as during continuous parenteral and enteral nutrition alone and in combination (transitional nutrition support).
Description of Actual Data Sample:
  • Initial N: 89 patients underwent IC and met criteria for study entry (46 males, 43 females)
  • Attrition (final N): 76 adults had evaluable sample data (42 males, 34 females). Thirteen were excluded for incomplete demographic or other data.
  • Age: Mean age 43±12 years
  • Other relevant demographics: Mean APACHE III score was 59±20 on day of measurement
  • Anthropometrics: Not obese; mean BMI 26±6
  • Location: Maryland.


Summary of Results:
  REE (kcal per Day) Percent MREE ME (Bias) MSE (Precision)
H-B without activity 1,572±318, P<0.001 79±2 -393 (-484 to -302) 18.8% (16% to 1.6%)
H-B x 1.2 1,889±381, P=0.08 95±2 -78 (-170 to 14) 16.1% (13.7% to 18.5%)
Ireton-Jones 1,811±200, P=0.003 91±1 -145 (-245 to -45) 17.1% (14.1% to 20.1%)
25kcal per kg per day 1,848±513, P=0.155 93±3 -123 (-229 to -17) 19.1% (16.2% to 22%)
Indirect calorimetry 1,982±545      


Other Findings

  • Average duration of IC measurement was 44±58 minutes
  • The Harris-Benedict equation multiplied by an activity factor of 1.2 was unbiased and precise, although it over-predicted at greater than 2,650 total kcal per day (P<0.001)
  • The Ireton-Jones equation was precise but biased, and it over-predicted at less than 1,750 total kcal per day (P=0.02) and under-predicted at greater than 1,750kcal per day (P<0.001)
  • The American College of Chest Physicians' consensus recommendation was biased and imprecise, over-predicted at REE greater than 2,050 total kcal per day (P<0.001)
  • The Harris-Benedict equation without an activity factor also demonstrated bias and imprecision. 
Author Conclusion:
Our results suggest that the Harris-Benedict equation, multiplied by an activity factor of 1.2, is suitable for predicting REE in patients with REE values less than 2,650 total kcal per day. This equation may be used in the absence of indirect calorimetry.
Funding Source:
Government: Dept. of Veterans
University/Hospital: Mont. Sinai Hospital
Reviewer Comments:
  • Valid IC protocol
  • Large sample size.
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? N/A
  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)? 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