CI: Best Method to Estimate RMR (2010)


Epstein CD, Peerless JR, Martin JE, Malangoni MA. Comparison of methods of measurements of oxygen consumption in mechanically ventilated patients with multiple trauma: The Fick method vs. indirect calorimetry. Crit Care Med. 2000; 28(5): 1,363-1,369. 

PubMed ID: 10834679
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 compare the measurements of whole body oxygen consumption determined by the Fick method and by indirect calorimetry in mechanically ventilated patients with multiple trauma.
Inclusion Criteria:
  • Mechanically ventilated adults with multiple injuries who received a pulmonary artery catheter within 24 hours of admission to the surgical ICU
  • Multiple sites of injury
  • Blunt mechanism of injury
  • Need for endotracheal intubation and mechanical ventilation
  • Insertion of flow-directed pulmonary artery and arterial catheters within 24 hours of admission
  • Age older than 18 years old.
Exclusion Criteria:
  • Patients with isolated head injuries, spinal cord injuries, penetrating injuries, and severe portal hypertension
  • No measurements made in patients who had visible air leaks in a thoracotomy drainage system or audible air leaks around the endotracheal tube cuff
Description of Study Protocol:


All mechanically ventilated patients with multiple trauma who were admitted to the surgical ICU of MetroHealth Medical Center were evaluated for study eligibility over a 24-month period.


Prospective cross-sectional study.


Oxygen consumption was measured by indirect calorimetry and the Fick method.

Statistical Analysis

  • Continuous variables examined for normality and homogeneity of variance by histograms, Z-score histograms, the Kolmogorov-Smirnov test and Bartlett's test
  • Scattergrams and linear regression plots were used to examine the relationship between VO2 values determined by the Fick method and by indirect calorimetry
  • Paired T-tests were performed for analysis of between-method differences in VO2 measurements at each time period
  • Sample size was estimated by power analysis based on Cohen's methods
  • The Bland and Altman technique was used to determine the limits of agreement between methods of measurement.
Data Collection Summary:

Timing of Measurements

After the initial resuscitation, simultaneous measurements of oxygen consumption by the reverse Fick equation and by indirect calorimetry were performed every six hours for 24 hours. Measurements were made within 24 hours of admission to surgical ICU.  

Dependent Variables

  • Oxygen consumption measured by indirect calorimetry using Puritan-Bennett 7250 Metabolic Monitor, calibrated automatically, in normothermic patients who were at rest for at least 30 minutes, measurements made when the FiO2 was lowered to 80%
  • Oxygen consumption was measured by reverse Fick equation.

Independent Variables

  • Post-operative measurements were delayed for six hours when patients had received inhalation anesthesia 
  • Measurements delayed for one hour in the event of a change in ventilator settings
  • At the time of measurement, patients remained in steady state for 30 minutes of post-event rest
  • During each measurement period, patient variables were recorded, including:
    • Quantities of IV fluids
    • Blood transfusions
    • Ventilator settings
    • IV medications for:
      • Inotropic support
      • Sedation
      • Analgesia
      • Chemical paralysis.
  • Injury Severity Score, Lung Injury Score and Post-injury Multiple Organ Failure Score were assessed.
Description of Actual Data Sample:
  • Initial N: 38 adult patients. Based on power analysis, a sample size of 42 patients was needed for a power of 84%
  • Attrition (final N): 38 adult patients (23 males, 15 females)
  • Age: Mean 59±7 years, range 19 to 85 years
  • Anthropometrics:
    • Mean Injury Severity Score: 31±13, range 10 to 57
    • Multiple Organ Dysfunction Score:  8±6, range two to 24
    • Lung Injury Score: 1.16±0.75, range zero to three.
  • Location: MetroHealth Medical Center, Ohio.


Summary of Results:
  Time 1 Time 2 Time 3 Time 4
Mean VO2: IC 172±38 170±31 170±32 169±29
Range VO2: IC 103 to 299 121 to 235 103 to 241 121 to 239 
Mean VO2: Fick 125±47 130±48 132±53 130±60
Range VO2: Fick 47 to 248 39 to 267 31 to 319 39 to 319
Mean difference 46 41 38 38
t 5.78 6.22 4.77 4.23
p <0.01 <0.01 <0.01 0.01

Other Findings

  • At each measurement period, the mean VO2 values determined by indirect calorimetry were significantly greater than the mean VO2 values determined by the Fick method:
    • Time 1: 172ml±38ml vs. 125ml±47ml per minute per m2, P<0.0001
    • Time 2: 170ml±31ml vs. 130ml±48ml per minute per m2, P<0.0001
    • Time 3: 17.0ml±32ml vs. 132ml±53ml per minute per m2, P<0.0001
    • Time 4: 169ml±29ml vs. 130ml±60ml per minute per /m2, P<0.0002.
  • By using the Bland and Altman technique, the mean bias was 41,l±3.95ml per minute per m2
  • Correlation coefficients of VO2 values between methods of measurements were statistically significant:
    • R2=0.32, P=0.0001
    • R2=0.32, P=0.0001
    • R2=0.33, P=0.0001
    • R2=0.18, P=0.0001.
  • No statistical association between the bias and Lung Injury Scores or Abbreviated Injury Scores were found. There was a significant inverse relationship between the mean pulmonary score of the Post-injury Multiple Organ Failure Score and the bias determined at the first measurement period.
Author Conclusion:
Indirect calorimetry should be the preferred standard for measurement of oxygen consumption in severely injured patients.
Funding Source:
Johnson & Johnson Medical
Pharmaceutical/Dietary Supplement Company:
Foundation associated with industry:
Reviewer Comments:
  • Simultaneous measurements and valid IC protocol
  • Statistical analysis was well done.
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? 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? Yes
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