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CI: Best Method to Estimate RMR (2010)

Citation:

Faisy C, Guerot E, Diehl JL, Labrousse J, Fagon JY.  Assessment of resting energy expenditure in mechanically ventilated patients. Am J Clin Nutr. 2003; 78: 241-249. 

PubMed ID: 12885704
 
Study Design:
Cross-Sectional Study
Class:
D - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To prospectively study the REE of mechanically ventilated patients in the ICU with the objective of identifying factors that might influence REE to propose an accurate method for calculating REE in patients receiving respiratory support.
Inclusion Criteria:
Metabolically stable adult patients who were intubated and mechanically ventilated for over 24 hours.
Exclusion Criteria:

Excluded for reasons leading to inaccurate REE measurements:

  • Hemodynamic instability
  • Respiratory instability
  • Variations in the carbon dioxide pool
  • An intravenous carbohydrate load more than 15kcal per kg per day
  • Air leaks around the respiratory circuit or visible air leaks in the chest-drainage system
  • Accumulation of intermediate metabolites
  • High level of inspired oxygen.
Description of Study Protocol:

Recruitment

Subjects recruited over one year in a university teaching hospital.

Design

Cross-sectional study.

Intervention

RMR measured with indirect calorimetry and estimated with equations.

Statistical Analysis

Measured and calculated REE were compared using two-way student's T-test, correlation coefficients and the Bland-Altman method. Sample size was calculated. Correlation coefficient R was calculated by using linear regression analysis. Bland-Altman analysis also used to determine the limits of agreement between measured and calculated REE. To identify variables significantly associated with MREE, we performed a univariate analysis with the nonparametric Mann-Whitney and Kruskal-Wallis tests for categorical variables and Spearman's correlation coefficient for quantitative variables. Multi-variate analysis was conducted with the use of a multiple linear regression model to determine the relations between MREE and patient data. 

Data Collection Summary:

Timing of Measurements

Prospective trial of indirect calorimetry measurements and information for equations.

Dependent Variables

  • RMR measured with indirect calorimetry using Puritan Bennett 7250 metabolic monitor, calibrated before each use, all measurements made between 4 p.m. and 6 p.m., patients were at rest and noise was avoided, REE measured over three consecutive 30-minute periods with four quality criteria to validate simultaneous measurements
  • Events leading to the cessation of IC measurements were occurrence of shock, accidental extubation, leaks of gas around the respiratory circuit, patient agitation and need for urgent diagnostic or therapeutic procedures 
  • RMR estimated with the Harris-Benedict equation, corrected for Long et al, defined hypermetabolism factors of 1.13 per degree Celsius over 37C°, 1.2 for minor surgery, 1.35 for major trauma or surgery and 1.6 for severe infection.

Independent Variables

  • Continuous enteral feeding stopped six hours before measurements
  • Immune deficiencies
  • Treatment for cancer
  • Use of catecholamines, vasopressors, theophylline, curare, sedatives or morphine
  • Documented infection
  • Caloric intake during previous 24 hours
  • Renal failure
  • Liver failure
  • Body temperature
  • Heart rate
  • Type of respiratory support
  • Respiratory rate
  • Minute ventilation
  • Level of positive-end expiratory pressure
  • Weight measured electronically
  • Height measured with tape measure
  • BMI
  • Body composition through bioelectrical impedance.
Description of Actual Data Sample:
  • Initial N: 132 patients intubated and mechanically ventilated for over 24 hours over a one-year period
  • Attrition (final N): A total of 70 patients were eligible (40 men, 30 women); 62 excluded based on exclusion criteria
  • Age: Mean 61±18 years
  • Location: France.

 

Summary of Results:

 Multivariate analysis:  independent variables determining REE in eligible patients

 

  Beta Coefficient Correlation Coefficient R2 Correlation Coefficient R 95% CI P-value
Intercept -4,834        
Weight (kg) 7.73 0.14 0.37 0.21, 0.53 <0.0001 
Height (cm) 13.90 0.11 0.33 0.17, 0.49 0.0002
Body temperature (C°) 93.78 0.07 0.27 0.10, 0.44 0.002
Minute ventilation (L per minute) 31.62 0.04 0.21 0.15, 0.39 0.01


Other Findings

  • A total of 1,260 REE measurements (five minutes) were completed; 128 (10%) were excluded based on not meeting quality criteria
  • Mean MREE and Harris-Benedict calculated REE differed significantly (1,890kcal±404kcal compared with 1,399kcal±243kcal per day, respectively, P<0.001). MREE was 25% higher than calculated with Harris-Benedict
  • Mean calculated REE from Harris-Benedict corrected according to Long et al was not significantly different from MREE (1,817kcal±528kcal compared with 1,890kcal±404kcal per day, respectively)
  • Calculated REE for Harris-Benedict strongly correlated to MREE (mean bias 491kcal±282kcal per day; 95% CI: 425kcal, 557kcal per day). Limits of agreement between two methods were -73kcal to 1,055kcal per day. The 95% CI for lower and upper limits of agreement ranged from -139kcal to -7kcal per day and from 989kcal to 1,121kcal per day, respectively.
  • Calculated REE for Harris-Benedict corrected according to Long et al were also correlated but less well (mean bias 73kcal±502kcal per day, 95% CI: -20kcal, 166kcal per day). Limits of agreement between two methods were -932kcal to 1,078kcal per day. The 95% CI for lower and upper limits ranged from -1,136kcal to -728kcal per day and from 874kcal to 1,282kcal per day, respectively
  • Multivariate analysis retained four independent variables defining REE: Body weight (R2 = 0.14, P<0.0001), height (R2=0.11, P=0.0002), minute ventilation (R2=0.04, P=0.01) and body temperature (R2=0.07, P=0.002)
  • New equation: REE (kcal per day) = (8 x body weight) + (14 x height) + (32 x minute ventilation) + (94 x body temperature) - 4,834 
  • REE calculated with this equation was well correlated with MREE (R2=0.61, P<0.0001)
  • Bland-Altman plots showed a mean bias approaching zero, and the limits of agreement between measured and predicted REE were clinically acceptable.
Author Conclusion:
The results of this study show that the REE of 70 mechanically ventilated patients was affected by only a few determinant variables (weight, height, body temperature and minute ventilation) and that usual predictive equations failed to accurately estimate REE in these patients. 
Funding Source:
University/Hospital: Hopital Europeen Georges Pompidou, Hotel Dieu
Reviewer Comments:
  • Well-defined inclusion and exclusion criteria
  • Valid IC protocol
  • Large sample size.
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? N/A
  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? 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