EE: Measurement Interval (2005)

Citation:

Frankenfield DC, Sarson GY, Blosser SA, Cooney RN, Smith JS. Validation of a five-minute steady state indirect calorimetry protocol for resting energy expenditure in critically ill patients. J Am College Nutr. 1996; 15: 397-402.

 
Study Design:
Retrospective Cohort Study
Class:
B - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

To validate, in critically ill patients, an abbreviated protocol that uses five consecutive stable one-minute readings of oxygen consumption [VO2, carbon dioxide production (VCO2, and minute ventilation (VE) in a range of ±5%, vs. a more standard protocol that uses 30 consecutive stable one-minute readings of VO2, VCO2 and VE in a range of ±10%].

Definitions

  • Rest: In ICU, often defined as a period when patient is left undisturbed before and during a 20- to 30-minute steady state measurement and is moving minimally or not at all during the test
  • Steady state: Patient is at rest and one period of five consecutive minutes in which the coefficients of variation for VO2, VCO2 and VE were equal to 5% or one period of 30 consecutive minutes in which the coefficients of variation were equal to 10%
  • Success group: Successfully completed both protocols; abbreviated and 30-minute protocol
  • Fail group: Completed only one protocol or failed one or both protocols.

If either a five- or 30-minute steady state test was not obtained, the study was considered a failure (Fail group).

Inclusion Criteria:
  • Mechanically, ventilated patients in adult surgical and medical ICU units
  • Not restless or agitated at the beginning of the indirect calorimetry
  • Patients receiving continuous enteral or parenteral feedings were not excluded or had feedings interrupted for study.
Exclusion Criteria:
  • Patents restless or agitated at beginning of IC
  • Patients were excluded if the fraction of inspired oxygen was greater than 0.60 or if there was an air leak via chest tubes or ventilator circuits.
Description of Study Protocol:

Anthropometric

Height, weight, ideal body weight: Not mentioned how they were obtained.

Clinical

  • Clinical data collected on all patients including:
    • Vital signs: Heart rate, respiratory rate, body temperature
    • Medications administered: 48% of patients were sedated (opiates, benzodiazapines, muscle relaxants, inotropes)
    • Nutritional intake: Data collected on nutrition support regimen including protein and non-protein calorie intake, route of administration (enteral or parenteral)
    • Ventilation parameters: Inspiratory oxygen fraction [FIO2, positive end-expiratory pressure (PEEP)], ventilator mode
  • Resting Energy Expenditure:
    • IC performed on resting, mechanically ventilated ill patients
    • IC type: Metabolic monitor
    • Equipment of calibration: Using standard gases prior to each measurement
    • Coefficient of variation using std gases: Yes
    • Rest before measure (state length of time rested if available): See definition of “rest”
    • Measurement length: 40 inches
    • Steady state: One period of five consecutive minutes in which the coefficients of variation for VO2, VCO2 and VE were equal to 5% and one period of 30 consecutive minutes in which the coefficients of variation were equal to 10% (Success group)
    • Fasting length: Continuous enteral and parenteral feedings
    • Exercise restrictions: Patients were bedridden; not applicable
    • Room temp: Hospital room temperature
    • Number of measures within the measurement period: Every minute; up to maximum 40 inches
    • Were some measures eliminated? Only the first successful five-minute steady state period was considered
    • Were a set of measurements averaged? IC data measured over five vs. 30 minutes for Success and Fail groups
    • Training of measurer? Not mentioned
    • Subject training of measuring process? Patients on ventilators.

Definitions

  • Rest In ICU, often defined as a period when patient is left undisturbed before and during a 20- to 30-minute steady state measurement, and is moving minimally or not at all during the test
  • Steady state: Patient is at rest and one period of five less than consecutive minutes in which the coefficients of variation for VO2, VCO2, and VE were less than 5% or one period of 30 consecutive minutes in which the coefficients of variation were less than 10%
  • Success group: Successfully completed both protocols; abbreviated and 30-minutes protocol
  • Fail group: Completed only one protocol or failed one or both protocols [If either a five- or 30-minute steady state test was not obtained, the study was considered a failure (“Fail group”)].
Data Collection Summary:

Outcome(s) and Other Measures

  • Oxygen consumption (VO2, carbon dioxide production (VCO2, minute ventilation (VE), respiratory quotient (RQ=VCO2 VO2 and energy expenditure were obtained with IC
  • Independent variables of weight, height, age, ideal body weight (IBW), % IBW, basal metabolic rate were calculated with Harris-Benedict equation
  • The mean values of oxygen consumption, carbon dioxide production, respiratory quotient, minute ventilation and resting energy expenditure obtained from five- and 30-minute protocols were calculated and compared for the Success and Fail groups
  • The first five-minute period in which coefficients of variation for VO2, VCO2 and VE were 5% or less was compared to the first 30-minute period in which coefficients of variation for these variables were 10% or less.

Statistical Tests

  • A power analysis indicated that a sample size of 23 would be necessary to detect a 10% difference between the measurement methods, alpha = 0.05 and beta = 0.8
  • Data from the five-minute and 30-minute steady state were compared using student’s paired T-test. Chi-square tests and regression analysis were also utilized. Statistical significance was established at P<0.05.

Measurement Process

  • Number of measurements: IC measured every minute; up to maximum of 40 minutes
  • Length of measurement: For a maximum of 40 minutes
  • Steady state:
    • 24 patients completed both protocols (70%)
    • 10 patients failed one or both protocols (30%)
    • Of the failures, three met the criteria for the 30-minutes steady state protocol and six met the criteria for neither steady state criteria
    • Overall, 80% of patients completed a five-minute steady state test, 74% completed a 30-minute steady state test and 18% completed neither test
    • Mean time to completion of a successful five-minute study period was 10.5+1.3 (range five to 27 minutes, median eight minutes)
    • Mean time to completion for successful 30-minute study period was 30.75+1.3 minutes (range 30 to 40 minutes, median 30 minutes)
    • Mean time savings was 20.2+1.3 minutes (range three to 26 minutes, median 23 minutes).

RQ

  • There were no significant differences in VE, VO2, VCO2, respiratory quotient or energy expenditure between the protocols in the Success group or in the Fail group
  • Success group: The mean difference between the five-minute and 30-minute protocols for VO2 was 0±2ml per minute (range –20 to 13ml per minute), VCO2 was –1±1ml per minute (range –13 to 17ml per minute); VE, 0.02±0.09 (range –0.9 to 1.6L per minute); RQ, –0.0004+0.0056 (range –0.03 to 0.03); and REE, –4±10kcal per day (range –122 to 74kcal per day)
  • Fail group: The mean difference between the five-minute and 30-minute protocols for VO2 was –2±5ml per minute (range –20 to 37ml per minute), VCO2, –1±6ml per minute (range –36 to 37ml per minute); VE, 0.33±0.32L per minute (range –1.4 to 1.9L per minute); RQ, 0.0009±0.013 (range –0.06 to 0.06); REE, –15±39kcal per day (range –170 to 272kcal per day)
  • Coefficients of determination (R2) for VO2 and VCO2 between the two methods in the Success group were 0.99
  • In the Fail group, R2 values ranged from 0.75 for VCO2 to 0.91 for VO2
  • Doses of the most commonly prescribed opiate, fentanyl, was significantly higher in the subset of patients who successfully completed at least one resting steady state protocol compared to the subset of patients who failed to complete either resting steady state protocol (p<0.05). Failure to achieve steady state may have been the result of patient agitation, pain or confusion.

Measurement Timing

  • Sleep or rest: Rest
  • Physical activity: Not applicable as ventilated patients
  • Nutritional intake: Patients receiving continuous parenteral or enteral feedings did not have those feedings interrupted for study
  • Individual Characteristics:
    • Circulatory hormones: Not discussed
    • Breathing ability: On ventilators
    • Medical tests/procedures: Not mentioned
    • Chemicals: 48% of patients were sedated
  • Previous studies have shown that 20- to 30-minute IC protocols for REE compare favorably to prolonged (8- to 24-hour) measurements of total energy expenditure. Shorter steady state measurements have been utilized but have not been validated.
  • Our results suggest that an abbreviated resting IC protocol of five consecutive minutes at steady state (with coefficient of variation of 5% or less) is equivalent to a longer protocol of 30 minutes at steady state (with coefficient of variation of 10% or less) in most sedated or medically paralyzed, intubated critically ill patients
  • A strong correlation existed between the five- and 30-minutes steady state measurements of the Success group. For instance, the standard deviation of the difference in VO2 between the five- and 30-minute steady state tests was ±8ml per minute, two standard deviations ±16ml per minute. Not only were 96% of the measured differences within two standard deviations of the mean, but these differences were at most 3.9% different from the mean 30-minutes steady state VO2. Agreement was similar for the calculated variables REE and RQ, respectively, 5.2% and 6.3% of the 30-minutes steady state means.
  • In this study, the traditional 30-minute protocol required 30 to 40 minutes to complete. The time savings achieved using the abbreviated protocol was approximately 20 minutes per measurement. Assuming 15 minutes of transport and set up between patients, the abbreviated protocol doubles productivity of the IC and operator.
  • Overall failure rate of the five-minutes steady state was 20%, compared to a failure rate for the 30-minutes steady state of 26%. It is unlikely that a meaningful five- or 30-minutes steady state measurement can be obtained in unsedated, uncooperative patients.
Description of Actual Data Sample:

Actual Sample

  • Total N=34 critically ill patients
  • N=20 males; N=14 females
  • Broken down into two groups based on success (completing both protocol) or failure (failed one or both protocol).

Success Group

  • N=24
  • N=14 Males
  • N=10 Females
  • Age: 53±4 years
  • Post-operative day: 7±1.

Fail Group

  • N=10
  • N=six males
  • N=four females
  • Age: 64±2 years (P=0.03 vs. success group)
  • Post-op day: 14±5.

Statistical Tests

  • Power analysis indicated that a sample size of 23 would be necessary to detect a 10% difference between the measurement methods, alpha=0.05 and beta=0.8
  • Student’s paired T-test. Chi-square tests and regression analysis were also utilized. Statistical significance was established at P<0.05.
Summary of Results:

Anthropometric

  • Success group
    • Height (cm): 172±2
    • Weight (kg): 81±7
    • Percentage ideal body weight (IBW): 120±9
    • Basal metabolic rate (kcal per day): 1510±76
  • Fail group
    • Height: 171±2
    • Weight: 77±5
    • Percentage IBW: 116±6
    • Basal metabolic rate: 1410±68.

Results

  • Measurement process:
    • Number of measurements: IC measured every minute; up to maximum of 40 minutes
    • Length of measurement: For a maximum of 40 minutes
    • Steady state: 24 patients completed both protocols (70%)
    • 10 patients failed one or both protocols (30%)
    • Of the failures, three met the criteria for the 30-minute steady state protocol and six met the criteria for neither steady state criteria
    • Overall, 80% of patients completed a five-minute steady state test, 74% completed a 30-minute steady state test; and 18% completed neither test
    • Mean time to completion of a successful five-minute study period was 10.5+1.3 (range five to 27 minutes, median eight minutes)
    • Mean time to completion for successful 30-minute study period was 30.75+1.3 minute (range 30 to 40 minutes, median 30 minutes)
    • Mean time savings was 20.2+1.3 minutes (range three to 26 minutes, median 23 minutes)
  • RQ: There were no significant differences in VE, VO2, VCO2 respiratory quotient or energy expenditure between the protocols in the Success group or in the Fail group
  • Success group: The mean difference between the five-minute and 30-minute protocols for VO2 was 0±2ml per minute (range -20 to 13ml per minute); VCO2, -1±1ml per minute (range –13 to 17ml per minute); VE, 0.02±0.09 (range –0.9 to 1.6L per minute); RQ, -0.0004±0.0056 (range –0.03 to 0.03) and REE -4±10kcal per day (range –122 to 74kcal per day)
  • Fail group
    • The mean difference between the five-minute and 30-minute protocols for VO2 was -2±5ml per minute (range -20 to 37ml per minute); VCO2, -1±6ml per minute (range -36 to 37ml per minute); VE 0.33±0.32L per minute (range -1.4 to 1.9L per minute); RQ, 0.0009±0.013 (range -0.06 to 0.06); REE -15±39kcal per day (range –170 to 272kcal per day)
    • Coefficients of determination (R2) for VO2 and VCO2 between the two methods in the Success group were 0.99
    • In the Fail group, R2 values ranged from 0.75 for VCO2 to 0.91 for VO2
    • Doses of the most commonly prescribed opiate, fentanyl, was significantly higher in the subset of patients who successfully completed at least one resting steady state protocol compared to the subset of patients who failed to complete either resting steady state protocol (p<0.05). Failure to achieve steady state may have been the result of patient agitation, pain, or confusion.
  • Measurement timing:
    • Sleep or rest: Rest
    • Physical activity: Not applicable as ventilated patients
    • Nutritional intake: Patients receiving continuous parenteral or enteral feedings did not have those feedings interrupted for study
    • Chemicals: 48% of patients were sedated.
Author Conclusion:
  • Previous studies have shown that 20- to 30-minute IC protocols for REE compare favorably to prolonged (8 to 24 hours) measurements of total energy expenditure. Shorter steady state measurements have been utilized but have not been validated.
  • Our results suggest that an abbreviated resting IC protocol of five consecutive minutes at steady state (with coefficient of variation of =5%) is equivalent to a longer protocol of 30 minutes at steady state (with coefficient of variation of  =10%) in most sedated or medically paralyzed, intubated critically ill patients
  • A strong correlation existed between the five- and 30-minute steady state measurements of the Success group. For instance, the standard deviation of the difference in VO2 between the five- and 30-minute steady state tests was ±8ml per minute, two standard deviations ±16ml per minute. Not only were 96% of the measured differences within two standard deviations of the mean, but these differences were at most 3.9% different from the mean 30-minute steady state VO2 Agreement was similar for the calculated variables REE and RQ, respectively 5.2% and 6.3% of the 30-minute steady state means.
  • In this study, the traditional 30-minute protocol required 30 to 40 minutes to complete. The time savings achieved using the abbreviated protocol was approximately 20 minutes per measurement. Assuming 15 minutes of transport and set up between patients, the abbreviated protocol doubles productivity of the IC and operator.
  • Overall failure rate of the five-minute steady state was 20%, compared to a failure rate for the 30-minutes steady state of 26%. It is unlikely that a meaningful five- or 30-minute steady state measurement can be obtained in unsedated, uncooperative patients.
Funding Source:
Industry:
Hershey
Food Company:
University/Hospital: Pennsylvania State
Reviewer Comments:

Strengths

  • Because subjects were chosen based on whether agitated or not, failure rate was lower than if measured all critically ill patients
  • Although small sample size, a power calculation was performed indicating that a sample size of 23 (24 were successful in this study) was necessary to detect a difference of ±10% with an alpha of 0.05 and a beta of 0.8
  • A coefficient of variation of 10% is generally accepted for 20- to 30-minute steady state study periods; 5% for five consecutive one-minute steady state protocol; thus taking into account the accuracy is a strength of this study.

Limitations

  • Minimally sedated, uncooperative or agitated patients are less likely to complete the resting protocol (20% failure in the present study)
  • Limited generalizability to the most critically ill, sedated or medically paralyzed mechanically ventilated patients (may not be applicable for patients with assisted ventilation or spontaneous breathing)
  • May not be applicable to patients with indwelling pulmonary artery catheters (VO2 does not correlate well with that from gas exchange measurements)
  • Factors such as organ dysfunction states; which may influence the test 
  • Height and weight (how were they obtained).
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? N/A
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? N/A
  1.3. Were the target population and setting specified? N/A
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? N/A
  2.2. Were criteria applied equally to all study groups? N/A
  2.3. Were health, demographics, and other characteristics of subjects described? N/A
  2.4. Were the subjects/patients a representative sample of the relevant population? N/A
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? 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? No
  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? 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? 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? N/A
  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? N/A
  7.2. Were nutrition measures appropriate to question and outcomes of concern? N/A
  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? N/A
  7.5. Was the measurement of effect at an appropriate level of precision? N/A
  7.6. Were other factors accounted for (measured) that could affect outcomes? N/A
  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? N/A
  8.2. Were correct statistical tests used and assumptions of test not violated? N/A
  8.3. Were statistics reported with levels of significance and/or confidence intervals? N/A
  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? 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? N/A
  9.2. Are biases and study limitations identified and discussed? N/A
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? N/A
  10.2. Was the study free from apparent conflict of interest? N/A