CI: Best Method to Estimate RMR (2010)


Casati A, Colombo S, Leggieri C, Muttini S, Capocasa T, Gallioli G. Measured versus calculated energy expenditure in pressure support ventilated ICU patients. Minerva Anestesiol. 1996; 62 (5): 165-170.

PubMed ID: 8937040
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 evaluate the usefulness of the modified Harris-Benedict formula predicting energy expenditure in non-paralyzed, pressure support ventilated, critically ill patients.
Inclusion Criteria:
Consecutive patients, without a previous history of chronic malnutrition, admitted to ICU for acute respiratory failure, requiring mechanical ventilation.
Exclusion Criteria:
  • Head and spinal traumatized patients
  • Need for inspired oxygen concentration higher than 0.55
  • Need for sedation or muscle relaxation to facilitate mechanical ventilation.
Description of Study Protocol:
  • Recruitment: Consecutive patients admitted to the ICU of a teaching hospital
  • Design: Cross-sectional study
  • Blinding used: Not applicable
  • Intervention: RMR measured with indirect calorimetry and estimated using equations.
Statistical Analysis
  • One-way ANOVA test (with Fisher test and Scheffe F-test for assessing differences between three groups), chi-square test, correlation coefficient (R), linear regression and bias (the mean difference between two methods) were used when indicated
  • A P-value of less than 0.05 was pre-determined as the acceptable level of significance.
Data Collection Summary:

Timing of Measurements

Indirect calorimetry and collection of data for estimation equations.

Dependent Variables

  • RMR measured with indirect calorimetry using the Datex Deltratrac, after 12 hours of rest and no nutrient administration, calibrated before each measurement, MREE calculated as the mean of two 30-minute measurements performed after fasting 
  • RMR was estimated using Harris-Benedict formula with corrections for "hospital activity" and "stress factor." Activity factor was 1.25 for all patients, while stress factor was 1.1, 1.2 or 1.4 for groups based on nutritional stress.
  • In each patient, a single correction factor was calculated dividing MREE by the original Harris-Benedict equation.

Independent Variables

  • Weight, height and age recorded upon admission
  • Patients endotracheally intubated and ventilation assisted by pressure support ventilation
  • Monitoring included electrocardiography, invasive arterial blood pressure, central venous pressure, arterial blood gas analysis
  • 24 hours after admission, the Simplified Acute Physiology Score (SAPS) was calculated as a prognostic index of the severity of the illness.
Description of Actual Data Sample:
  • Initial N: 55 patients, divided into three groups on the basis of nutritional stress
  • Attrition (final N): 55; 29 men, 26 women
  • Age: Non-surgical non-septic patients, 57±19 years; complicated surgical patients, 58±16 years; severe infectious/multiple trauma patients, 53±17 years
  • Ethnicity: Not mentioned
  • Other relevant demographics: Non-surgical/non-septic patients (N=10), complicated surgical patients (N=21), severe infectious/multiple trauma patients (N=24)
  • Anthropometrics: Groups were homogeneous with respect to age, weight, height and male-to-female ratio, none of the patients exceeded 10% IBW. SAPS score was significantly higher in the severe infectious/multiple trauma patients.
  • Location: Italy.
Summary of Results:
  Non-Surgical/Non-Septic Complicated Surgical Severe Infectious/Multiple Trauma ANOVA
SAPS 11±3 13±3



Original H-B (kcal/day)





Modified H-B (kcal/day)





MREE by IC (kcal/day) 1,726.0±82.8 1,819.4±92.3 2,134.5±87.5 P=0.009
Modified H-B minus MREE by IC 175.1±82.03 324.5±64.5 336.7±62.9 P=0.0001
Correction Factor 1.20±0.041 1.28±0.03 1.50±0.04 P=0.0001

Other Findings

In each group, a good correlation between calculated and measured EE was found:
  • Non-surgical/non-septic: R=0.809; P=0.0046; bias, 175.1±82kcal per day
  • Complicated surgical patients: R=0.753; P=0.0001; bias, 324.5±64.5kcal per day
  • Severe infectious/multiple trauma patients: R=0.711; P=0.0001; bias, 366.7±62.9kcal per day
  • The mean difference value seems to be increased in the more stressed patients, but these differences did not reach statistical significance (P=0.23).
A single correction factor for the original Harris-Benedict formula was also calculated on each group:
  • Non-surgical/non-septic: 1.20±0.04
  • Complicated surgical patients: 1.28±0.03
  • Severe infectious/multiple traume patients: 1.50±0.04, P=0.0001.
Author Conclusion:
  • The use of both "stress" and "activity" correction factors seems to be excessive in pressure support ventilated patients
  • A single correction factor, proportional to the intensity of the illness, should be used in mechanically ventilated patients
  • Compared to the Harris-Benedict formula, we found an energy expenditure increment of about 20%, 30% and 50%, respectively, in non-septic/non-complicated, surgical complicated and multiple trauma/septic patients.
Funding Source:
University/Hospital: University of Milano, IRCCS
Reviewer Comments:
Valid IC protocol; fasting state.
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? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  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? N/A
  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? 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