EE: Respiratory Quotient (RQ) (2013)


Brandi LS, Bertolini R, Santini L, Cavani S. Effects of ventilator resetting on indirect calorimetry measurement in the critically ill surgical patient. Crit Care Med. 1999;27(3):531-539.

PubMed ID: 10199532
Study Design:
Randomized Controlled Trial
A - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To evaluate the effect of acute change in minute ventilation (Ve on oxygen consumption (VO2, carbon dioxide production (VCO2, respiratory quotient, and energy expenditure during volume-controlled mechanical ventilation in the critically ill surgical patients.
Inclusion Criteria:
  1. Understand and give written consent.
  2. Adults surgical patients who had undergone major vascular or abdominal surgery, were mechanically ventilated, and were considered stable by their physician.
Exclusion Criteria:
  1. Refusal to consent
  2. Not meeting inclusion criteria
  3. Conditions such as: hemodynamically unstable, required high doses of vasoactive medications (>5 ug/kg/min dopamine or dobutamine), required fluids or colloid solutions to maintain their perfusion pressure, were mechanically ventilated with pressure support ventilation and intermittent mandatory ventilation , required inspired oxygen concentrations (FiO2 >60%, and were ventilated with peak airway pressure >60 cm H2O.
Description of Study Protocol:
  • Randomization: a random sampling formed 2 groups: increased Ve group and reduced Ve group.
  • The study consisted of 2 periods: a basal period of stability (baseline) and a period of ventilator resetting lasting 120 mins.
  • During this period, all measurements were obtained every 15 mins, performed in the supine position.
  • All pts were adequately sedated and paralyzed.


  • Ht, Wt, body surface area


  • Temperature, VCO2 VO2 RQ, EE

Resting energy expenditure

  • Equipment of Calibration: not specified
  • Coefficient of variation using std gases: Not specified
  • Rest before measure (state length of time rested if available): Sedated and paralyzed
  • Measurement length: 120 mins
  • Steady state: Likely
  • Fasting length: not specified
  • No. of measures within the measurement period: 8
  • Were some measures eliminated? No
  • Were a set of measurements averaged? Yes, 6 measurements taken at every 15 mins
  • Coefficient of variation in subjects measures? Yes 8.2±1.9%VO2 1.9±0.8% CO2
  • Training of measurer: Likely
  • Subject training: No 


Not specified

IC type: Nellcor Puritan Bennett 7250. been validated and tested for accuracy and reproducibility.
Data Collection Summary:

Outcome(s) and other measures

  • VO2 VCO2 RQ, Exhaled Ve.

Blinding used: No; the study design do not allows “blinding.”

Description of Actual Data Sample:
  • N=20 (18 males, 2 females)
  • Approximate age range of group: 66-74 y
  • (Analyst note: range established using mean ±SEM)
  • Statistical tests:
  • Students’ t test
  • One way ANOVA
  • Two way ANOVA
  • Least square regression analysis
Summary of Results:
  • Demographic and baseline info (±SEM or standard error of mean)
  • Exhaled ventilation (Ve) change group
  • Increased Ve Decreased Ve
  • N=10 N=10
  • Male/female 9/1 9/1
  • Age 72.0±2.1 69.4±2.8
  • Wt (kg) 71.9±8.8 67.8±2.5
  • Ht (cm) 172±2.2 168±2.0
  • VO22.9±.15 3.0±.18
  • VCO22.5±.10 2.7±.17
  • RQ 0.87±.02 0.88±.02
  • EE(kcal/min) 1.02±.07 1.01±.05

No significant differences were noted between 2 groups.

VO2 and EE

Despite large change in Ve, VO2and energy expenditure did not change significantly either in increased or in the reduced Ve group.

VCO2 and RQ


VCO2normalized in the reduced Ve group, bur remained higher than baseline in the increased Ve group.

VCO2: VCO2increased by 10.5±1.1% in the increased Ve group (p<0.01), and decreased by 12.4±2.1% in the reduced Ve group (p<0.01).



RQ did not normalize in both groups and remained significantly different from baseline at the end of the study.


Measured within 18-24 hrs after surgical procedures.

Similarly, RQ increased by 16.2%±2.3% (from 0.87±0.02 to 1.02±0.02) (p<0.01) in increased Ve group, and decreased by 17.2%±1.8% (0.88±0.02 to 0.73±0.02; (p<0.01)
After 15 min ventilator resetting, VCO2and RQ changed significantly between ventilatory exhalation levels.
Author Conclusion:

“We concluded that, during controlled mechanical ventilation, the time course and the magnitude of the effect on gas exchange and energy expenditure measurements caused by acute changes in Ve suggest that VO2and energy expenditure measurements can be used reliably to evaluate and quantify metabolic events and that VCO2and respiratory quotient measurements are useless for metabolic purposes at least for 120 mins after ventilator resetting.”


“Two limitations of our study need to be addressed. First, to evaluate the effects of ventilator resetting, we have chosen ventilatory manipulations that are not usually used in the clinical practice. It remains to be seen whether smaller changes in Ve can in any way affect RQ and VCO2measurements.”

“Second, the quantitative aspect of our results obtained in surgical patients could not be applied to other categories of ICU patients. However, as long as the CO2and O2stores of the body have the same dynamics independently of the clinical condition, the response after a change in the ventilator parameters may lead to effects similar to those observed in our patients.”
Funding Source:
Government: MIUR
University/Hospital: University of Pisa
Reviewer Comments:


  • Limitations of the study were fully discussed and considered in the interpretation of the results.
  • Clinically relevant.
  • Randomization was done and two groups were assessed for comparability.
  • Sophisticated statistics.
  • Conclusions were consistent with the data.


Generalizability was limited to surgical patients and note that patients were able to breathe on own.
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