EE: Duration of Measurement (Steady State) (2013)

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

Aim of study was to:

  1. To test a short indirect calorimetry protocol with 5 stable 1-minute readings (5-min steady state) against the commonly used protocol of 30 1-min readings (30-min steady state) in critically ill patients with various modes of ventilation


Steady state: 5-min steady state defined as the first 5 consecutive stable 1-min readings with a coefficient of variation =5% for VCO2and VO2The first five and 15 1-min readings were also tested without considering a 5-min steady state phase but using the same criteria used to define a 5-min steady state test.

Successful test: Defined so if there was a period of 30 consecutive minutes with a coefficient of variation =10% for VCO2and VO2.
Inclusion Criteria:
  1. Critically ill patients admitted to the medical ICU
  2. Only pressure-controlled and pressure support ventilation modes were considered.
  3. Major diagnoses: septic shock, (20 in Group A, 6 in Group B); severe sepsis (18 in Group A, 16 in Group B); congestive heart failure (2 in Group A, 8 in Group B); pneumonia (2 in Group A, 7 in Group B); chronic obstructive lung disease (6 in Group B); and hepatic coma (1 in Group A).
  4. All patients in Group A and 48.8% in Group B received some form of analgosedation (doses in mg/kg per minute); midazolam, ketamine or fentanyl.
Exclusion Criteria:
  1. Patients ventilated with an inspiratory oxygen fraction (FIO2>0.6 or positive end-expiratory pressure (PEEP) >10 cm H2O with chest tubes, or with gross inconsistencies in their vital signs were excluded.
  2. Febrile or agitated patients
Description of Study Protocol:


  • Ht measured? Not discussed
  • Wt measured? Not discussed
  • Fat-free mass measured? Not discussed


  • Ventilator function tested? Breathing frequency, tidal volume, and FIO2 cuff pressure of the tracheal tube was controlled and if needed, adjusted before IC
  • Monitored heart rate? not discussed
  • Body temperature? not discussed
  • Medications administered? All patients in group A, but only 48.8% of those in group B received some form of sedation medication and the doses were significantly higher in group A. Mechanically ventilated patients were usually sedated with midazolam in combination with ketamine or fentanyl or alone; if necessary a muscle relaxant was given.

Resting energy expenditure (REE): IC

  • IC type: Hood—Deltatrac II MBM-200 Metabolic Monitor
  • Equipment of Calibration: Gas calibration done before each measurement with a standard calibration gas (95% O2 5% CO2
  • Coefficient of variation using std gases: Yes =10%
  • Rest before measure (state length of time rested if available): Patients left undisturbed for at least 30 min and ventilator parameters unchanged for 60-90 min before starting with and during the calorimetry test
  • Measurement length: Between 7 and 8 am after the patient was awake for about an hour; at least 35 min
  • Steady state: 5-min steady state and 30-min steady state
  • Fasting length: overnight (group C)
  • Exercise restrictions: not mentioned
  • Room temp: under room temperatures in half darkened room and quiet environment
  • No. of measures within the measurement period: at least 35 consecutive minutes; first 5 minutes discarded
  • Were some measures eliminated? The first 5 minutes of data were discarded to exclude artifacts during connecting the calorimeter to the patient.
  • Coefficient of variation in subjects measures? The test was considered a success if there was a period of 30 consecutive minutes with a coefficient of variation of =10% for VCO2and CO2. A 5-min steady state was defined as the first five consecutive stable 1-min readings with a coefficient of variation of =5% for VCO2and VO2.
  • Training of measurer? Not mentioned
  • Subject training of measuring process? Not mentioned
  • Intervening factor: If mechanically ventilated patients were tested in both controlled and assisted ventilation modes, at least 24 hours elapsed between each test
Data Collection Summary:

Outcome(s) and other measures

  1. Values for VO2 VCO2, minute ventilation (VE)(in mechanically ventilated patients), respiratory quotient (O2) and energy expenditure (EE) were recorded every minute.
  2. Data for body temperature, body weight, vital signs, the Sequential Organ Failure Assessment (SOFA) score, and dose of sedatives and neuromuscular blockers were collected during each test.
  3. Mechanically ventilated patients were tested in either controlled or assisted or in both modes.
  4. The data were then classified into group A (controlled) or group B (assisted) according to the ventilation mode.

Blinding used: No

Description of Actual Data Sample:
  • N=46 mechanically ventilated patients and 16 spontaneously breathing patients
  • Patients classified into groups according to ventilation modes or spontaneously breathing

Group A and B (Group A controlled, and B assisted)

  • Total: 46 mechanically ventilated patients (28 males and 18 females; aged 59.7±18.9 y)
  • Sequential Organ Failure Assessment (SOFA) score for group A: 11.6±4.4
  • SOFA score for group B: 7.7±3.5 (group A significantly higher than B; p=0.001).

Group C

  • 16 spontaneously breathing patients
  • (7 males and 9 females; aged 50.9±15.8 y)
  • SOFA score for Group C: 3.8±3.1
  • Statistical tests: Student t-test, Fisher exact test, and linear regression analysis was utilized.
  • P value of <0.05 was considered significant.
Summary of Results:


Not discussed.

For groups A and B, there was a total of 86 tests with 43 in each group. 40 patients were tested in both controlled and assisted modes, three each in controlled or assisted modes only.

The test was successful in all cases of group A and in 36/43 (84%) cases in group B.

Taking group A and B together, sedation had a significant influence on the success of the 30-min steady state test (p=0.001).

For Group C, the 30-min steady state IC was successfully completed in only 12/16 patients (75%); failure due to discomfort.

Among the patients with unsuccessful 30-min steady state test, 5-min steady state readings could be obtained in only one of the seven “failures” in group B, but in all of those in group C.


  • Resting energy expenditure: Correlation between 5-min REE (kcal/d) and 30-min REE (kcal/d):

Group A

  • y=0.982x +23.871
  • r2=0.972; p<0.001
  • n=43

Group B

  • y=1.016x +20.917
  • r2=0.977; p<0.001
  • n=35

Group C

  • y=1.001 x –27.67
  • r2=0.994; p<0.001
  • n=12

There was a highly significant correlation between the 5-min and 30-min steady state data (p<0.0001).

The 30-min steady state test was 100%, 83.7%, and 75% successful in group A, B, and C, respectively.

The corresponding rate for the 5-min steady state test was 100%, 81.4%, and 100%, respectively for group A, B, and C.

The coefficient of determination (r2) for REE between the 2 protocols ranged between 0.972 and 0.994.

The time required to collect the 5-min steady state data was 5.5±1.1, 9.9±5.7, and 6.5±3.3 min for group A, B, and C, respectively.

For all mechanically ventilated patents, there was a significant but weak negative linear correlation between the time needed to complete the 5-min steady state on the one side and the dose of sedation (r2=0.123, p=0.007), the SOFA score (r2=0.128, p=0.001), or both (r2=0.209, p=0.002) on the other side.

Author Conclusion:

“In this study we have shown that a 5-min steady state indirect calorimetry could be successfully conducted in critically ill patients with different modes of ventilation.

Sedation influenced the success and the time required in mechanically ventilated patients.

In patients on controlled mode (usually sedated), a short period was enough, while those on assisted mode (usually less sedated or not sedated) often moved their extremities for various reasons, their breathing was not regular or they coughed, resulting in the need for a longer period.”

“In our study, most of the patients were suffering from pulmonary dysfunction. Remaining quiet for 30 min with the hood over the face may be uncomfortable for them, so that the standard used on healthy subjects is not applicable in every case. In our study, 25% of these patients did not tolerate the standard procedure. Therefore, an abbreviated test protocol may be a promising alternative.

“Adding the mean ±SD to the 5-min routinely discarded at the start, a test period of about 12 min in a controlled mode, 21 min in an assisted mode, and 15 min in spontaneously breathing patients would be enough for a successful abbreviated protocol in the majority of cases.

In conclusion, the abbreviated indirect calorimetry protocol allows an efficient use of manpower, time and technique in ICU patients with different modes of ventilation without and significant loss of data quality. It would be more acceptable to spontaneously breathing patients.”

“Indirect calorimetry with 5-min steady state test correlated very well with the 30-min steady-state test in both mechanically ventilated and spontaneously breathing patients.”

“The time required varies depending on the mode of ventilation, and it is influenced by the level of sedation in mechanically ventilated patients.”

“The abbreviated protocol may be more acceptable to spontaneously breathing patients.”
Funding Source:
University/Hospital: University of Leipzig (Germany)
Reviewer Comments:


  • Small sample sizes when categorized by mode of ventilation
  • Limited generalizability; critically ill patients with specific diagnosis
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? 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? 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