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CI: Best Method to Estimate RMR (2010)

Citation:

Frankenfield D, Smith JS, Cooney RN.  Validation of 2 approaches to predicting resting metabolic rate in critically ill patients.  JPEN 2004;28(4):259-64. 

PubMed ID: 15291408
 
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 test the validity of calculation equations, posing 2 questions:

  1. Which equation resulted in the highest percentage of accurate estimations (wherein calculated metabolic rate was <10% different from measured)?
  2. Which equation had the smallest number of large errors (wherein calculated metabolic rate was >15% from measured)?
Inclusion Criteria:
Mechanically ventilated surgical, trauma and medical patients.
Exclusion Criteria:
None specifically mentioned.
Description of Study Protocol:

Recruitment

Data in current study compiled during course of routine clinical care in surgical and medical ICUs between 2000 and 2003.

Design

Cross-Sectional Study.

Blinding used (if applicable)

Not applicable.

Intervention (if applicable)

RMR measured using indirect calorimetry and estimated with equations. 

Statistical Analysis

Estimated RMR within 10% of measured was considered accurate, whereas estimations >15% different from measured were considered large errors.  Bias and precision were evaluated after methods of Sheiner and Beal.  An equation was considered unbiased if the 95% confidence interval of the mean difference between predicted and measured RMR included 0.  Precision was defined as a 95% confidence interval for absolute difference between measured and predicted RMR <10% of the measured RMR.

Data Collection Summary:

Timing of Measurements

RMR measured with indirect calorimetry and estimated using several equations, using current or admission body weight, whichever was lower so as not to account for excess body water.

Dependent Variables

  • RMR measured with indirect calorimetry using Deltatrac 101 Metabolic Monitor, all tests performed by same person, calibrated before each test, there were no air leaks, and fraction of inspired oxygen was <60%, individual tests included if coefficient of variation for oxygen consumption and carbon dioxide production on a 30-minute test was <10%, or a 5% coefficient of variation on a 5-minute test, first 5 minutes discarded in all tests 
  • RMR estimated using Ireton-Jones equations from 1992 and revised equations from 1997
  • RMR estimated using 3 versions of a multivariate Penn State equation, based on Harris-Benedict or Mifflin-St. Jeor equations, using actual weight in nonobese and adjusted weight in obese patients 
  • RMR estimated using unmodified Mifflin-St Jeor and Harris-Benedict equations

Independent Variables

  • Subjects were at rest - a period of time when subject was not moving and had not been significantly disturbed for previous 20 minutes
  • Feedings were not stopped for the measurements

Control Variables

 

Description of Actual Data Sample:

Initial N: 47 subjects were measured

Attrition (final N):  47 subjects, 28 men, 19 women

Age:  43% were 65 or older, with a mean age 77 +/- 7 years, range 65 - 87 years.  Those under 65 had a mean age of 44 +/- 15 years, range 16 - 64 years.

Ethnicity: not mentioned

Other relevant demographics:  38% were obese, 6% were underweight

Anthropometrics:

Location:  Pennsylvania 

 

Summary of Results:

 

Equation

Difference (kcals) Bias, 95% CI for difference (kcals) Absolute difference (kcals) Absolute difference, % of RMR Precision, 95% CI for absolute difference, % of RMR
Ireton-Jones 1992 3 +/- 316 (-814 to 760) -90 to 96 257 +/- 197 13 +/- 10 10-16
Ireton-Jones 1997 -237 +/- 326 (-1051 to 487) -333 to -142 316 +/- 248 15 +/- 10 12-18
Penn State 1998 4 +/- 208 (-606 to 439) -57 to 65 156 +/- 136 8 +/- 6 6-9

Penn State 2003a

-15 +/- 211 (-433 to 468)

-78 to 46

166 +/- 128 8 +/- 6

6-10

Penn State 2003b

-13 +/- 226 (-408 to 503)

-79 to 54

183 +/- 131 9 +/- 6

7-11

Other Findings

All equations were linearly associated with measured RMR.  The unmodified Harris-Benedict and Mifflin St. Jeor equations correlated with RMR with a R2 of 0.69.  The Penn State equations, which use the Harris-Benedict equation, increased the R2 to 0.81.  The Ireton-Jones equation correlations were R2 of 0.57 (1992 equation) and 0.54 (1997 equation), p < 0.05 for all.

A larger percentage of subjects were estimated accurately by the Penn State equations (72% in the best equation) than by the Ireton-Jones equations (60% in the best equation, not significant).

The incidence of errors >15% of measured was significantly lower in the Penn State equation (11% of subjects) compared with the Ireton-Jones equation (32% of subjects, p < 0.05).

The 1998 and 2003a Penn State equations were unbiased and precise.  The Ireton-Jones 2002 equation was unbiased but not precise (95% confidence interval for absolute difference was 10% to 16% of measured RMR), whereas the 1997 Ireton-Jones equation was neither unbiased nor precise.

 

Author Conclusion:
The 2003a Penn State equation for estimating RMR in mechanically ventilated, critically ill patients was the most accurate of the equations tested and seems to be a valid clinical tool in the absence of indirect calorimetry measurements.  The equation uses the Harris-Benedict equation using actual body weight in obese and non-obese subjects, minute ventilation, and maximum body temperature in the following form:  RMR = HBE(0.85) + VE(33) + Tmax(175) - 6433.  Using this equation, the practitioner can expect to predict RMR to within 10% of actual in about 80% and to within 15% of actual in about 100% of nonobese patients.  However, because of a tendency to inaccuracy in the obese, consideration should be made in obese people for opting for hypocaloric regimens that avoid use of illness-modified equations.  The 1992 Ireton-Jones equation was less accurate than the 2003a Penn State equation (specifically in nonobese and elderly subjects) but was more accurate than the 1997 revised Ireton-Jones equation.
Funding Source:
University/Hospital: Milton S. Hersey Medical Center, Pennsylvania State University
Reviewer Comments:
Inclusion/exclusion criteria not well defined, but large sample size.  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? N/A
  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? ???
  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? 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? N/A
  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