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CI: Best Method to Estimate RMR (2010)

Citation:

Frankenfield David. Validation of an equation for resting metabolic rate in older obese critically ill patients. JPEN. 2010 (in press).

 
Study Design:
Diagnostic, Validity or Reliability Study
Class:
C - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

Test the validity of a modified Penn State equation to more accurately predict measured energy expenditure in older and obese critically ill patients.

Inclusion Criteria:
  • Critically ill on mechanical ventilator
  • BMI: 30 kg/m2 or higher
  • Age: 60 years or higher.
Exclusion Criteria:
  • Not on mechanical ventilation
  • BMI less than 30kg/m2
  • Age less than 60 years
  • Air leak
  • Fraction of inspired oxygen higher than 60%
  • Change in ventilator setting had occurred within the previous hour.
Description of Study Protocol:

Recruitment

Patients admitted to intensive care unit (informed consent waived by IRB).

Design

Concurrent comparative study.

Blinding Used

Indirect calorimetry standardized test.

Intervention

None except application of predictive equation to estimate energy needs.

Statistical Analysis

  • Bias of equations calculated as 95% CI of difference between estimated and measured metabolic rate; if 95% CI included zero, the measure was unbiased
  • Precision calculated as the 95% CI of the percent absolute difference between estimated and measured values (root mean squared prediction error or RMSPE); if 95% CI was less than or equal to 15%, the equation was considered precise
  • Percentage of estimates falling within 10% of measured (accuracy) and percentage of estimates greater than 15% greater than measured was tabulated.
Data Collection Summary:

Timing of Measurements

Indirect calorimetry measurements made between hours of 5:30 A.M. and 7:30 A.M. using an open-circuit indirect calorimeter and followed evidence-based recommendations for measurement of RMR made by the American Dietetic Association.

Dependent Variable

The calculated difference between each predicted energy expenditure equation and the actual measured energy expenditure.

Independent Variables

  • Modified Penn State equation that uses Mifflin St. Jeor equation for healthy people: RMR (kcal per day) = Mifflin(0.71) + Tmax(85) + Ve(64) - 3,085
  • Original Penn State equation: RMR (kcal per day) = Mifflin(0.96) + Tmax(167) + Ve(31) - 6,212.
  • Mifflin St. Jeor equation:
    • Men: 10(weight) + 6.25(height) - 5(age) + 5
    • Women: 10(weight) + 6.25(height) - 5(age) - 161.

Tmax = maximum body temperature in the previous 24 hours (degrees Centigrade).

Ve = minute ventilation recorded from ventilator in L per minute.

 

Description of Actual Data Sample:

Initial N

  • New Data: 50 (46% male)
  • Revalidation:
    • 74 Penn State (modified for BMI of 30kg/m2 or higher and age 60 years or older)
    • 106 original Penn State equation.

Age

70±7 years.

Other Relevant Demographics

  • 18% trauma victims
  • 48% surgical patients
  • 34% medical patients
  • 76% received continuous infusions of fentanyl, benzodiazepines or propofol
  • 36% of patients were febrile at some point in the 24 hours prior to the study, but only 14% were febrile at time of the study
  • Mean SOFA score 9±3 (range four to 18)
  • Current body temperature (oC) 37.0±0.9 (range 34.9 to 38.5)
  • Maximum body temperature (oC) 37.6±0.8 (range 35.9 to 39.0)

Anthropometrics

  • 30% had BMI of 40kg/m2 or higher in the 24 hours prior to the study, but only 14% were febrile at time of the study
  • BMI of 38.4±7.2kg/m2 (range 30.0 to 60.9).

Location

Penn State Milton S. Hershey Medical Center Hershey, PA.

Summary of Results:

Key Findings for New Patients (N=50)

Variables

Penn State (Modified for BMI ≥ 30kg/m2 and Age ≥ 60 Years) N=50

Measures and Confidence Intervals

Penn State N=50

Measures and Confidence Intervals

P-Value

Bias (95% CI)

-120 to -12 kcal per day (biased)

-90 to 25 kcal per day (unbiased)

N/A

Precision (95% CI for root mean squared prediction error)

 7%  to 10%

7% to 10%

 N/A

Accuracy

70% 

66% 

P=0.832

Incidence of large errors 16% 10% P=0.370
Accuracy in patients with BMI > 40kg/m2 (N=15) 73% 80% Not given
Maximum errors in patients with BMI > 40kg/m2 (N=15) -0.18 +0.19 Not given

 Other Findings for New and Archived Subjects  

Variable

Penn State (Modified for BMI ≥ 30 kg/m2 and age ≥ 60 years)

N=74

Penn State

N=106

P-Value

Measured RMR kcal per day as mean ± SD (range)

2,014±365 (1,317 to 2,996) 1,996±440 (1,116 to 3,882) N/A
Calculated Penn State kcal per day as mean ± SD (range) 1,968±325 (1,360 to 2,668) 1,996±367 (1,286 to 2927)  
Ratio between Penn State and measured as mean ± SD (range) 0.98±0.09 (0.82 to 1.19)

1.00±0.13 (0.68 to 1.48)

N/A
Bias for patients BMI ≥ 40kg/m2 (95% CI) -87 to -4 kcal per day (biased) -90 to 25 kcal per day (unbiased) N/A

Precision (95% CI for root mean squared prediction error)

6% to 9% 9% to 12%  
Overall accuracy (%) for BMI ≥ 30kg/m2 and age ≥ 60 years) 74% 58% P=0.04
Incidence of large errors for patients BMI ≥ 30kg/m2 and age ≥ 60 years) 12% 22% P=0.084
Accuracy for patients BMI ≥ 40kg/m2 (%) 68% 67%  

Both equations were precise, with identical 95% CI for root mean squared prediction error 7% to 10%.

Author Conclusion:

The Penn State (modified) equation should be used for patients 60 years or older with BMI of 30kg/m2 or higher. For patients less than 60 years with any BMI, the original Penn State equation should be used if indirect calorimetry is not available or practical.

Funding Source:
University/Hospital: Penn State Milton S. Hershey Medical Center
Reviewer Comments:
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.) Yes
  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")? Yes
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? N/A
  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%.) N/A
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? N/A
  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? Yes
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.) Yes
  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? Yes
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? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  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? N/A
  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? Yes
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? N/A
  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)? Yes
  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? N/A
  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