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EE: Thermic Effect of Feeding (2013)


Frankenfield DC, Ashcraft CM. Description and prediction of resting metabolic rate after stroke and traumatic brain injury. Nutrition. 2012 Sep; 28(9): 906-911.

PubMed ID: 22464552
Study Design:
Diagnostic, Validity or Reliability Study
C - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
  • To determine whether stroke is a hypermetabolic event in mechanically ventilated patients
  • To determine what clinical factors explain the variation in the resting metabolic rate after brain injury
  • To test the use of an established equation to predict the resting metabolic rate in mechanically ventilated and critically ill, brain-injured patients.
Inclusion Criteria:
  • Traumatic or non-traumatic (stroke) brain injury
  • Had been in the critical care unit for no longer than six days
  • Mechanically ventilated
  • Receiving nutritional support or had written orders to initiate nutritional support
  • Informed consent was waived because the study was of minimal risk.
Exclusion Criteria:

Not described.

Description of Study Protocol:


Patients were recruited from the Penn State Milton S. Hershey Medical Center.


Diagnostic, validity or reliability study.

Blinding Used

Implied with measurements


  • Indirect calorimetry was conducted prospectively in mechanically ventilated patients within the first six days of admission to a critical care unit owing to ischemic stroke, hemorrhagic stroke, isolated traumatic brain injury, or traumatic brain injury with collateral injuries
  • Clinical data were collected simultaneously and a predicted value of the resting metabolic rate was calculated using the Penn State equation (using body size, body temperature and minute ventilation).

Statistical Analysis

  • An analysis of proportions was used to analyze all frequency data (P<0.05)
  • The general linear model of analysis of variance (ANOVA) was used for the analysis of the resting metabolic rate
  • Two fixed factors were of interest in this study: type of injury
    • Schemic stroke, hemorrhagic stroke, isolated traumatic brain injury or multiple traumas including brain injury
    • The use or absence of continuous sedation
  • Two possibly confounding events were tested with ANOVA before the analysis of the brain injury types
  • The bias between the predicted and the measured metabolic rates was measured by examining the 95% CI of the mean differences between the two values
  • Limits of agreement were calculated according to the Bland-Altman method, being ±1.96 SD from the mean difference between the measured and calculated resting metabolic rates. 
Data Collection Summary:

Timing of Measurements

Indirect calorimetry was performed in the early morning (5:30 to 7:30 AM), according to best practice methods.

Dependent Variables

  • Resting metabolic rate calculated from the oxygen consumption and the carbon dioxide production using the equation of Weir:
    • The Deltatrac MB-100 open-circuit indirect calorimeter was used for all studies
    • Measurements were conducted for 30 minutes and resting steady-state conditions had to be met within that time
    • Rest was defined as a period in which the patient was not disturbed by family or caregivers, movement was minimal and a steady state was achieved
    • Patients were clothed in hospital gowns and usually light blankets
    • Continuous feeding infusions were not interrupted for the study, but if the feeding was interrupted as part of the clinical care, the measurement proceeded anyway
    • A steady state was defined as a coefficient of variation of 10% or less for oxygen consumption and carbon dioxide production
    • If the measurement was interrupted or the patient started to move, two other steady-state definitions were allowed (10 minutes of measurement with a coefficient of variation within 10%, or five minutes with a coefficient of variation within 5%)
    • The first five minutes of each test was automatically discarded in all cases
    • Body temperature, minute ventilation, heart rate, mean arterial pressure, laboratory data, sedation use, inotrope use, current Glasgow Coma Scale score, height, weight, age and reason for admission were also collected at the time of the indirect calorimetric measurement.
  • The Mifflin equation was inserted into the Penn State equation in order to predict the metabolic rate of the critically ill, mechanically ventilated patient.

Independent Variables

Critically ill, mechanically ventilated patients suffering from:

  • Ischemic stroke
  • Hemorrhagic stroke
  • Isolated traumatic brain injury
  • Traumatic brain injury with collateral injuries.
Description of Actual Data Sample:
  • Initial N: 130 patients
    • 30 in the ischemic stroke group
    • 36 in the hemorrhagic stroke group
    • 32 in the isolated traumatic brain injury group
    • 33 in the traumatic brain injury group).
  • Attrition (final N): 130 patients
  • Age: Mean age:
    • Group One: 67±15 years
    • Group Two: 55 ±17 years
    • Group Three: 52±23 years
    • Group 4: 44±19 years.
  • Anthropometrics: Mean BMI (kg/m2):
    • Group One: 31.4±7.7
    • Group Two: 30±6.9
    • Group Three: 26.9±4.3
    • Group Four: 28±6.0.
  • Location: Hershey, Pennsylvania.
Summary of Results:

Key Findings

  • Ischemic stroke showed a lower incidence of fever, a lower body temperature, and a lower resting metabolic rate than the other groups, whereas in hemorrhagic stroke these variables were similar to the trauma groups
  • Sedation decreased the resting metabolic rate, but this effect seemed particular to the trauma patients
  • The Penn State equation predicted the resting metabolic rate accurately 72% of the time and when its component variables of body temperature and minute ventilation were controlled in an analysis of variance all the differences among the brain injury and sedation groups were eliminated
  • At the time of the study, 10 patients had been without feeding in the 24 hours prior to measurement; at the conclusion of the measurement, six patients were found to have been overfed
  • An analysis of the resting metabolic rate by the feeding level showed:
    • 2,002±425kcal per day for the unfed group
    • 1,810±418kcal per day for the overfed group
    • 1,982±249kcal per day for all other patients.
Author Conclusion:
  • Stroke is a hypermetabolic state event most of the time. Body size, temperature and minute ventilation explain most of the variation in the resting metabolic rate after traumatic and non-traumatic brain injuries. The Penn State equation therefore predicts the resting metabolic rate in brain-injured patients no matter the mechanism of injury.
  • In the present study, all patients were intubated and receiving feeding through an enteral tube, all feedings were delivered continuously and overfeeding occurred in fewer than 5% of patients. The metabolic rate was not different between the patients who received feeding and those few who did not.
  • Since feedings were not interrupted during the measurements, there is the potential for a thermogenic effect of feeding to have increased the metabolic rate in the present study. However, several factors mitigate this:
    • The thermogenic effect of feeding is minimized by tube feeding vs. eating
    • It is further minimized by continuous rather than bolus feeding
    • The thermogenic effect of feeding is less pronounced if overfeeding is avoided.
Funding Source:
University/Hospital: Penn State Milton S. Hershey Medical Center
Reviewer Comments:

Large number of patients in study.

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? ???
  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? ???
  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")? Yes
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? 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? 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? 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? 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