CI: Best Method to Estimate RMR (2010)

Study Design:
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Quality Rating:
Research Purpose:
The primary aims of the study were to compare the number of kJ patients received via enteral feedings with the patients' estimated energy requirements as indicated by the Harris-Benedict equation and by indirect calorimetry and to determine the factors that affect enteral feeding delivery in patients receiving mechanical ventilation.
Inclusion Criteria:
  • 18 years or older
  • Intubated and receiving mechanical ventilation
  • Receiving enteral tube feedings at the prescribed goal rate


Exclusion Criteria:
  • If receiving parenteral or oral feedings at the time of enrollment
  • IC measurements excluded for unstable or high (>80%) levels of inspired oxygen, early discontinuation of mechanical ventilation, unavailability of a technician, cuff leaks, patient agitation, unstable hemodynamic condition
Description of Study Protocol:


Convenience sample of 60 adults, data collected between May 2001 and October 2002.  Patients were selected from 3 15-bed ICUs located at 2 study sites:  the medical-surgical ICU at the Palo Alto Veterans Affairs Health Care System hospital and a coronary care unit and a medical ICU in a county hospital.


Cross-Sectional Study.

Blinding used (if applicable)

Not applicable.

Intervention (if applicable)

Energy received via enteral feedings recorded for 3 consecutive days, and energy requirements determined by Harris-Benedict equation and indirect calorimetry.

Statistical Analysis

Descriptive statistics were used to characterize the sample.  Chi-square and independent sample t tests were used to determine the differences between patients who had indirect calorimetry and those who did not.  Two-tailed, paired Student's t tests were used to determine differences between mean energy required and mean energy received.  Multiple linear regression analysis was used to examine the effects of clinical predictor variableson the percentage of required enteral feeding actually received.  The sample size for a multiple linear regression model that included 4 predictors with an R2 of 0.4 was 60.

Data Collection Summary:

Timing of Measurements

Energy received via enteral feedings recorded for 3 consecutive days, and energy requirements determined by Harris-Benedict equation and indirect calorimetry.

Dependent Variables

  • RMR measured by indirect calorimetry in subset of 25 patients using Vmax 29n Spectra metabolic cart, calibrated before each measurement, measured continuously for 30 minute period with first 5 minutes discarded, steady state achieved (defined as <10% change in oxygen consumption and carbon dioxide over 5 minute period)
  • RMR estimated using Harris-Benedict formula and stress related factors ranging from 1.3 to 1.5 

Independent Variables

  • Enteral feedings: type, date and time began, date and time goal rate achieved
  • Age
  • Height
  • Weight
  • Sex
  • BMI
  • Hospital and ICU admission dates
  • Diagnosis at admission and/or surgical procedure
  • Values on Simplified Acute Physiology Score II
  • 7 patients received continuous sedation during study period

Control Variables


Description of Actual Data Sample:

Initial N: 60 patients, indirect calorimetry in subset of 25

Attrition (final N):  60, 52 men, 8 women

Age:  mean 63.9 +/- 12.9 years

Ethnicity:  83.3% White, 5.0% Black, 8.3% Hispanic, 3.3% Asian/Pacific Islander 

Other relevant demographics:  mean SAPS II score = 37.1 +/- 11.6

Anthropometrics:  There were no statistically significant differences between patients whose energy requirements were determined by both Harris-Benedict and indirect calorimetry and those who did not have an indirect calorimetry measurement.

Location:  California


Summary of Results:


 Variable Energy requirements t  P

 95% CI

 Estimated REE (n=60)  8996 +/- 1326 kJ (2150 +/- 317 kcal) 8.911  <0.001  2397 - 3787 kJ (573 - 905 kcal)

 Mean 3-day intake

 5899 +/- 3058 KJ (1410 +/- 731 kcals)




 Measured REE (n=25)

 6853 +/- 1946 kJ (1638 +/- 465 kcals)




 Mean 3 day intake  6342 +/- 2598 kJ (1516 +/- 621 kcals)      

 Other Findings

Mean estimated energy requirements (8996 +/- 1326 kJ) and mean energy intake received (5899 +/- 3058 kJ) differed significantly (95% confidence interval 3297 - 3787, P < 0.001).

A total of 41 patients (68.3%) received less than 90% of their required energy intake, 18 (30.0%) received within +/- 10%, and 1 (1.7%) received more than 110%.

Episodes of diarrhea, emesis, large residual volumes, feeding tube replacements, and interruptions for procedures accounted for 70% of the variance in energy received (P < 0.001).

Procedural interruptions alone accounted for 45% of the total variance.

Estimated energy requirements determined via indirect calorimetry and mean energy received did not differ.

When energy requirements estimated by using the Harris-Benedict equation with measured REEs in these 25 patients, the energy requirements were overestimated by a mean of 2042 kJ (488 kcal) when the Harris-Benedict equation was used.  The 2 values differed significantly [95% CI 1251 - 2837 kJ (299 - 678 kcal) P < 0.001].


Author Conclusion:
Most critically ill patients receiving mechanical ventilation who are fed enterally do not receive their energy requirements, primarily because of frequent interruptions in enteral feedings.  We found that more than 2/3 of ICU patients treated with mechanical ventilation received less than 90% of their nutritional requirements, as determined by using the Harris-Benedict equation, via enteral tube feeding; half of these patients received less than 50% of their required energy during the 3 day study period.
Funding Source:
Reviewer Comments:
More than half of the sample was excluded from indirect calorimetry, but there were no statistically significant differences.  Valid IC protocol.
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) 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? Yes
  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.) Yes
  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? Yes
  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)? 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