CI: Best Method to Estimate RMR (2010)

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To compare the oxygen consumption index measured by using indirect calorimetry with a portable metabolic cart and calculated according to Fick's principle in critically ill patients.
Inclusion Criteria:
Critically ill patients of both sexes, victims of trauma or sepsis who required prolonged, mechanical ventilation (more than 3 days) and invasive hemodynamic monitoring with a Swan-Ganz catheter admitted to the University Hospital.  When respiratory and hemodynamic stabilization occurred within 3 days of admission, the patients were included in the study. 
Exclusion Criteria:
  • Clinically contraindicated invasive hemodynamic monitoring
  • Age > 80 and < 15 years
  • The need for FiO2 (oxygen fraction of inspired air) > 0.6
  • Mean arterial pressure < 50 mm Hg
  • Heart rate <50 or > 140 bpm
  • Presence of a bronchopleural air fistula
  • Irreversible circulatory shock
  • Brain death
  • Refusal to participate in the study by the patient or person legally responsible
Description of Study Protocol:


Methods not described - admitted to University Hospital.


Cross-Sectional Study.

Blinding used (if applicable)

Not applicable.

Intervention (if applicable)

RMR measured using indirect calorimetry and estimated with Fick's method.

Statistical Analysis

Data analyzed statistically considering the mean values of 4 serial measurements of oxygen consumption index obtained for all patients by the 2 methods.  The 2 methods were compared by using the nonparametric Wilcoxon test based on the null hypothesis and with a 95% confidence interval.  Differences were considered significant at P < 0.05.

Data Collection Summary:

Timing of Measurements

Oxygen consumption obtained using both methods in 4 serial measurements.

Dependent Variables

  • Invasive hemodynamic monitoring through insertion of Swan-Ganz catheter into pulmonary artery and measured using thermodilution technique
  • RMR measured with indirect calorimetry using Deltatrac II Metabolic Monitor, with initial calibration performed before study protocol using alcohol burning test, as well as calibrated before each measurement, patient in stable condition in a calm environment, with no manipulations of the upper airways or of the respirator parameters for at least 30 minutes, measurements lasted 30 minutes

Independent Variables

  • APACHE II score, Injury Severity score, Sepsis score
  • Patient weight was estimated based on BMI according to age

Control Variables


Description of Actual Data Sample:

Initial N: 14 patients (10 men, 4 women)

Attrition (final N):  14 patients.  5 were trauma victims, 9 sepsis victims.

Age:  mean age 39.4 +/- 5.4 years

Ethnicity:  not mentioned.

Other relevant demographics: mean APACHE II score = 21.3 +/- 1.8, mean Injury Severity Score = 24.8 +/- 6 and sepsis score = 19.6 +/- 2.3.

Anthropometrics (e.g., were groups same or different on important measures)

Location:   University Hospital, University of Sao Paolo, Brazil 

Summary of Results:



Time 1 Time 2 Time 3 Time 4

IC Mean +/- SD

138 +/- 28 141 +/- 27 144 +/- 26 145 +/- 24

IC Range

91 - 176

94 - 174

102 - 183

112 - 170

Fick's Mean +/- SD

159 +/- 38

155 +/- 26

158 +/- 35

162 +/- 26

Fick's Range 102 - 211 108 - 185 94 - 240 117 - 207
Difference 21 14 14 17

Other Findings

A good correlation was found between the 2 methods (r = 0.77) for the mean of the 4 serial measurements.

No statistically significant differences were observed between indirect calorimetry and Fick's equation at T1 (IC:  138 +/- 28 vs Fick:  159 +/- 38 ml/min/m2, P = 0.10) and T3 (IC = 144 +/- 26 vs Fick: 158 +/- 35 ml/min/m2, P = 0.14) but a significant difference was observed at T2 (IC: 141 +/- 27 vs Fick: 155 +/- 26 ml/min/m2, P = 0.03) and T4 (IC: 145 +/- 24 vs Fick: 162 +/- 26 ml/min/m2, P = 0.01). 

The mean difference between the measurements at times T1 to T4 was 17 +/- 4 ml/min/m2 (10 +/- 2%).

Author Conclusion:
In conclusion, the present results indicate the existence of a good correlation between VO2 obtained by indirect calorimetry and by the Fick method, with the possibility of using indirect calorimetry as a method for the assessment of this parameter in critically ill patients as effectively as when using the reverse Fick equation, with the advantage that calorimetry is a noninvasive method free of complications.
Funding Source:
Government: FAPESP
Reviewer Comments:
Well-defined inclusion/exclusion criteria.  Valid IC protocol.  Small sample size, but 4 serial  measurements made per patient.
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? ???
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? Yes
  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? Yes
  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)? 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