CI: Best Method to Estimate RMR (2010)

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To determine which commonly used prediction equations for patients of normal weight were the best estimates of energy expenditure when compared with measured resting energy expenditure in a heterogeneous group of critically ill, underweight male patients.
Inclusion Criteria:
Underweight, critically ill male patients.  Only men were included in this analysis due to limited data for women (n=3).
Exclusion Criteria:
Patients with body weight >90% IBW based on Hamwi.  Only results with an FiO2 of <70% were included in the analysis.
Description of Study Protocol:


Critically ill patients admitted to a tertiary-care hospital in the Pacific Northwest from 1992 - 2003.


Cross-Sectional Study, Retrospective Analysis.

Blinding used (if applicable)

Not applicable.

Intervention (if applicable)

A comparison of 4 energy-prediction equations against MREE determined via indirect calorimetry. 

Statistical Analysis

Differences between MREE and the prediction equations were tested by repeated-measures ANOVA with post hoc pairwise comparisons using Bonferroni adjustment.  Data are presented as mean +/- SD.  Regression analysis was conducted between the predicted and MREE values.  The mean prediction error (MREE - predicted energy needs) was calculated to evaluate the tendency to over- or underestimate energy needs.  Level of significance set at p < 0.05.

Data Collection Summary:

Timing of Measurements

Retrospective analysis of indirect calorimetry measurements compared with equations.

Dependent Variables

  • RMR measured with indirect calorimetry using DeltaTrac, 3-4 carts used over study period, calibrated according to manufacturer's instructions, performed by trained respiratory therapists, all patients in steady state for >10 minutes, and had stable R value of <1.0
  • RMR estimated with Harris-Benedict equation using both current weight and IBW for patients <90% IBW, and adjusted body weight ([current body weight + IBW]/2) for patients <85% IBW
  • RMR estimated with Ireton-Jones equation for all mechanically ventilated patients (n=37) 

Independent Variables

  • All patients received nutrition support while indirect calorimetry performed

Control Variables


Description of Actual Data Sample:

Initial N: 42 critically ill male patients, 37 mechanically ventilated

Attrition (final N):  42 males

Age:  59.5 +/- 17.3 years

Ethnicity:  Not mentioned

Other relevant demographics:  Severely underweight, mean weight 57.97 +/- 8.31 kg, 77.1 +/- 9.7% IBW as determined by Hamwi, mean BMI 18.4 +/- 2.5 


Location:  Montana


Summary of Results:


  MREE (kcals) I-J (kcals) HB(CBW) HB (IBW) HB (ABW)
Sample Size  n = 42  n = 37  n=42  n = 42  n = 31



 1900.2  1349.4





 207.1  183.9



Minimum  1203  1658  1053  1228  1160
Maximum  2899  2612  1801  2001  1787

Other Findings

The Harris-Benedict formula using IBW, current weight and adjusted body weight was significantly different (p < 0.05) than MREE.

The Ireton-Jones equation was not significantly different (p > 0.05) from MREE but tended to overestimate energy needs (109.3% +/- 16.8% MREE).

Conversely, using the current weight or the IBW in the Harris-Benedict equation underestimated the patient's energy needs (77.0% +/- 11.6% MREE and 90.9% +/- 16.1% MREE, respectively).

For patients <85% IBW, use of the adjusted body weight in the Harris-Benedict equation represented 84.2% +/- 13.9% MREE.

The average caloric need was 31.2 +/- 6.0 kcal/kg current body weight.

The mean prediction error for all subjects was 110.1 for the Ireton-Jones equation, -440.7 for Harris-Benedict with current body weight, and -204.7 kcals/day for Harris-Benedict with IBW.

All equations were significantly correlated (p < 0.05) with MREE (r = 0.61 for Ireton-Jones, r = 0.67 for Harris-Benedict with current body weight, and r = 0.53 for Harris-Benedict with IBW).

For patients <85% IBW, the mean prediction error was -314.8 kcal/day for the Harris-Benedict equation with adjusted body weight, which was significantly correlated with MREE (r = 0.57, p < 0.05).


Author Conclusion:
No one prediction equation can be universally applied to all underweight patients without over- or underestimating energy needs for some or all of the patients.  A combination of prediction equations tempered with clinical judgment and the judicious use of indirect calorimetry, when feasible, remains the best method of predicting energy needs at this time.  Although these results were derived from a heterogeneous group of patients, the findings support the need to conduct a tightly controlled prospective study to develop an appropriate prediction equation for critically ill, underweight patients.  All patients should be continuously monitored to assess the appropriateness of the nutrition prescription, including caloric intake, and changes made when indicated by the patient's medical status or metabolic tolerance to the nutrition therapy. 
Funding Source:
University/Hospital: Montana State University, Sacred Heart Medical Center
Reviewer Comments:
IC protocol not completely described, especially for ventilated patients.  Data collected over 11 year time span with different respiratory therapists and different metabolic carts.  No standardization as to when the measurements were completed.
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? N/A
  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? ???
  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? ???
  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? ???
  7.7. Were the measurements conducted consistently across groups? ???
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