EE: Duration of Measurement (Steady State) (2013)
Citation:
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
- To determine whether energy expenditure determined from five minutes of measurement with less than 5% variation was similar to energy expenditure determined from a longer measurement period
- To determine what duration of energy expenditure measurements with coefficients of variations of 5% to 20% is required to achieve a standard error of the mean of 3% (by generating a statistical model using computer stimulation).
Inclusion Criteria:
Intubated patients in intensive care unit who were being assessed for nutrition support.
Exclusion Criteria:
Not meeting inclusion criteria.
Description of Study Protocol:
Recruitment
Retrospective review of results of indirect calorimetry for 47 consecutively intubated patients in the intensive care unit.
Design
Correlational study.
Statistical Analysis
- Pearson correlation coefficient to indicate relationship between the mean of the five-minute period and the mean of the entire study period
- Percent difference between the two values for each patient determined according to methods described by Bland et al
- Statistical model using a computer simulation was generated to determine what duration of energy expenditure measurements with coefficients of variation of 5% to 20% is required to achieve a standard error of the mean of 3%:
- Energy expenditure was assumed to be randomly distributed about a mean value
- Random data were generated within each specified magnitude of coefficient of variation (±5%, 10%, 15% and 20% of the mean value), representing a one-minute value of energy expenditure
- A random number was generated repeatedly for each data set within the specified magnitude of coefficient of variation and a "rolling" calculation of the mean and standard error of the mean of all previously generated random numbers was performed, representing consecutive minutes of measurement of energy expenditure
- The generation of random numbers within a specified magnitude of coefficient of variation was stopped once the standard error of the mean was 3%
- For each specified magnitude of coefficient of variation, 1,000 such data sets were generated and the minutes of measurement required to achieve a 3% standard error of the mean in 95% of cases were noted.
Data Collection Summary:
Timing of Measurements
One measurement time, on weekday mornings from 8:00 A.M. to 12:00 P.M.
Dependent Variables
- Difference between the short mean and long mean of energy expenditure measurement:
- Short mean: Energy expenditure determined from five minutes of measurement with less than 5% variation in minute-to-minute measurements
- Long mean: Energy expenditure determined from a longer measurement period (average duration of 31±13 minutes)
- Correlation between between short mean and long mean.
Independent Variables
- Measured REE [(VO2 L per minute), VCO2 (L per minute; ml per kg per minute), RQ, ventilation (L per minute)]
- IC type: Deltatrac Metabolic Monitor
- Equipment of Calibration: Medical-grade gas (96% O2 and 4% CO2)
- Coefficient of variation using std gases: Yes
- Number of measures within the measurement period: Not specified; to continue measuring energy expenditure until a period of five consecutive minutes of readings with a coefficient of variation of 5% or less occurs
- Were some measures eliminated? Not stated
- Were a set of measurements averaged? Yes, five consecutive minutes of readings were averaged when stable measurements occurs (coefficient of variation of 5% or less)
- Coefficient of variation in subjects measures? Yes
- IC measurements were made on week-day mornings from 8:00 A.M. to 12:00 P.M. All measurements were obtained by one person
- Patients were not purposefully sedated, but sedation was used for routine care
- Nursing interventions (i.e., suctioning, turning or dressings) were not allowed during the study periods.
Description of Actual Data Sample:
- Initial N: N=47 patients in intesive care unit (gender not reported)
- Final N: N=47
- Location: Vancouver, British Columbia, Canada.
Summary of Results:
- The correlation coefficient was 0.983, P<0.00001, for the relationship between the mean of the five-minute period and the mean of the entire study period
- The difference between short mean and long mean was less than 5% for 42 of 47 patients; the difference was more than 10% for two patients
- The difference between the mean values of the five-minute period and the entire study period was -2.6±60kcal per day (mean ±SD; P was not significant)
- The statistical model showed that for energy expenditure variation of 5%, 10%, 15% and 20%, the necessary durations of measurement to achieve a 3% error were 3, 9, 16 and 25 minutes.
Statistical Model
- The measurement duration required to achieve a 3% standard error of the mean in 95% of cases is five minutes for a 5% coefficient of variation
- It increases to 25 minutes for a 20% coefficient of variation.
Author Conclusion:
- We found that the mean of a five-minute period of measurement of energy expenditure with a CV of 5% or less is the same as the mean of a longer measurement period of 31±13 minutes
- A 25-minute measurement of energy expenditure is required to achieve a 3% SEM with variation coefficients as high as 20%
- We concluded that energy expenditure may be determined using the mean of a five-minute period of measurement if variation in that measurement is less than 5%. Larger variation requires longer period of time.
- Even with measurement variability as great as ±20%, a reliable value of energy expenditure is assured with measurement duration of 25 minutes
- Variations of minute-to-minute readings are associated with patient agitation, restlessness and movement.
Funding Source:
University/Hospital: | University of British Columbia (Canada) |
Reviewer Comments:
Agree with authors’ conclusions based on the study design, well conducted statistical test, and the valid statistical model.
Strengths
- Good measurement reliability and validity, appropriate statistical test
- The process of computer simulation to estimate the duration of measurements was well explained.
Generalizability/Weaknesses
- The measurement recommendation can only be applied to critically ill patients. MD referral bias related to request for nutrition support assessment.
- Demographic information was not reported in detail
- Did not discuss potential intervening factors for the two patients whose CV was higher than 10%.
Quality Criteria Checklist: Primary Research
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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? | No | |
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? | No | |
2.2. | Were criteria applied equally to all study groups? | ??? | |
2.3. | Were health, demographics, and other characteristics of subjects described? | No | |
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? | N/A | |
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? | N/A | |
5. | Was blinding used to prevent introduction of bias? | No | |
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? | 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? | 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? | 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? | 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? | ??? | |
7.7. | Were the measurements conducted consistently across groups? | N/A | |
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? | No | |
9.1. | Is there a discussion of findings? | Yes | |
9.2. | Are biases and study limitations identified and discussed? | No | |
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 | |