EE: Respiratory Quotient (RQ) (2013)


McClave SA, Lowen CC, Kleber MJ, CmConnell , Jung LY, Goldsmith LJ. Clinical use of the respiratory quotient obtained from indirect calorimetery. J Parenter Enteral Nutr. 2003;27(1):21-26.

Study Design:
Cross-Sectional Study
B - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
  1. To determine the overall clinical use of RQ as a marker for under- and overfeeding
  2. Monitor adequacy and tolerance of nutrition support.


  • Steady state: defined as VO2and VCO2of <15% and a change in RQ <10% over a consecutive 5-minute interval
  • Degree of feeding: Calories provided/calories required times 100:
    •   Under: <90% calorie requirements
    •   Appropriate: ±10%
    •   Over: >110% of calorie requirements
Caloric requirements: measured RMR plus 10% for pt activity.
Inclusion Criteria:
  1. Understand and give written consent
  2. Diseases in subjects that were allowed:
  3. Medications allowed: not reported.
Exclusion Criteria:
  1. Refusal to consent
  2. Receiving any nutrients from oral diet
  3. IC measure exclusions: Medical/surgical instability, fraction of inspired oxygen (FiO2=60%, positive end expiratory pressure =5 mm Hg, Failure to cooperate, Agitation, seizure activity or spasticity
  4. Pt were excluded after IC testing if there was nonphysiologic data (defined by measured overall RQ <0.67 or =1.3)
Description of Study Protocol:


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



  • Monitored heart rate? Not specified
  • Body temperature? Not specified
  • Medications administered?

Resting energy expenditure

  • IC type: Medtech or Medgraphics MMC
  • Equipment of Calibration: yes
  • Coefficient of variation using std gases: No
  • Rest before measure (state length of time rested if available): Not specified but some likely since reports “end point”
  • Measurement length: 5 mins
  • Steady state: Yes
  • Fasting length: MNT
  • Exercise restrictions XX hr prior to test? Not applicable
  • Room temp: Not specified
  • No. of measures within the measurement period:
  • Were some measures eliminated? Yes
  • Were a set of measurements averaged? 5 1-minute measures?
  • IF avg, identify length of each measure & no. of measurements?
  • Coefficient of variation in subjects measures? No
  • Training of measurer? Likely
  • Subject training of measuring process? No


  • Parenteral, enteral or both nutrition support types
  • Intervening factor:
Data Collection Summary:

Outcome(s) and other measures

  1. Measured REE [(VO2 l/min), VCO2 (l/min; ml/kg/min), RQ, ventilation (l/min)].
  2. Arterial blood gas (ABG)
  3. Serum ketones and electrolyte panel
  4. Urine urea nitrogen
  5. Nonprotein RQ calculated froma modified Lusk table.

Blinding used: No

Description of Actual Data Sample:
  • N=335 pts entered
  • Final sample size: 263
  • Age: 70.2±14 yr
  • Range: 19-100 y
  • N=57.4 males; N=42.6% females
  • Admitted into facility who required TPN or ETF(enteral tube feeding).
  • 88.6% on mechanical ventilation (MV)

Reasons for MV

  • Nonspecific respiratory failure: 59.4%
  • COPD exacerbation: 28.4%
  • Post-traumatic respiratory fx, CHF, pneumonia: 12%

Type of nutrition support

  • Enteral nutrition (EN): 92%
  • Parenteral nutrition (PN): 5.3%
  • Both routes: 2.7%

72 were excluded based on IC results; 28 because of nonphysiologic results (RQ out of range), and 44 failure to reach steady state.

Statistical tests

Pearson correlation, Spearman correlation, receiver operating characteristic curves, stepwise linear regression.

Summary of Results:

Pattern measured RQ in response to degree of feeding

  Measured overall RQ, %
Measured overall RQ, %
Measured overall RQ, %
Underfdg           (n=90) 60.0 32.2 7.8

Appropriate (n=64)

57.8 39.1 3.1

Overfdg            (n=109)

28.4 43.1 28.4

*statistically significant relationship b/t degree of feeding and overall measured RQ (P<0.0001).

  • There was a gradual upward shift in the measured RQ as degree of feeding increases. Note: an RQ >1.0 with underfeeding does not make sense physiologically and may represent inaccurate data.
  • The wide spread in measured RQ for each subset of pt clearly demonstrates RQ is not reliably reflected in the same manner in all patients in response to under- or overfeeding.

Correcting for nonprotein metabolism

  • Correcting for protein metabolism (nonprotein RQ) using 24-hr UUN did not improve correlation. A single measured RQ in a specific range would not reliably distinguish under/over-feeding from appropriate feeding.

Comparison of measured nonprotein RQ to reference range for predicted nonprotein RQ using Lusk talbe and percent fat/CHO infused

Measured overall NPRQ, %*


Measure NPRQ below range %

Measure NPRQ in range %

Measure NPRQ above range %

N         60         173       30


68         35         18


18         32        7


14         33         75
Acid/base disturbance

Metab acidosis

0           2          1

Metab alkalosis

39         29         28



50         40         43


11         11         19
  • Only 32% of patients being fed appropriate fell within the appropriate range; leaving 67.7% unable to differentiate from appropriate vs. inappropriate feeding.
  • In 30 pts (11.4%), the NPRQ fell outside the reference range.
  • Theroretically, comparison of the measured NPRQ to the reference predicted value might be useful in identifying clinical factors of hypo-/hyper ventilation which may artifactually influence IC measures. The incidence of metabolic acidosis/alkalosis or hypo-/hyperventilation was the same regardless of whether the measured NPRQ fell above, below or within the range.
  • In individuals that did show a degree of respiratory intolerance or ventilatory compromise, increases in RQ did correlate significantly to increasing respiratory rate (P=0.002, r2=0.04) and decreasing tidal volume (p=0.002, R2=0.04, suggesting shallow, rapid respirations in response to increases in measured overall RQ.
Author Conclusion:

As stated by the author in body of report

  • “Many factors exist that may displace the measured RQ that is difficult to identify clinically. . .inter-patient variability may exist within a single disease process. [Other factors include] pharmacologic agents (ethanol or propofol, both which reduce RQ), stress caused by acute diseases and defects in metabolism prevent lipogenesis, no effect seen with surplus dietary fat or difficulties with digestive assimilation with EN.”
  • “Of greatest clinical importance was those patients who experienced elevation of the RQ in response to overfeeding, significant increases in respiratory rate and decrease in tidal volume were seen”
  • “One of the major clinical benefits of the measured RQ is to validate an IC study confirming that the measured values for RQ fall in the physiologic range; measured values that fall outside this range are non-physiologic, infer serious problems with test validity and invariably represent error and artifactual influences.. The RQ should never be used to “fine-tune” the nutrition support regimen . . . the best way to determine the adequacy of nutrition support is to compare the amount of calories infused with the caloric requirements as measured by IC.”
Funding Source:
University/Hospital: University of Louisville, Kindred Healthcare
Reviewer Comments:


  • Large sample size
  • Adheres to IC measurement calorimetry procedures
  • Discusses withdrawal or those ineligible for study.



  • Questionable validity of indirect calorimeter
  • Generalizable to critically ill patients on mechanical ventilators that meet criteria for obtaining an accurate IC measure
  • “Study biases include the elimination of individuals who completed IC that had measures outside of physiological range so clinical application may see higher frequency of non-phsyiological measures?
  • An intervening variable not measured were types of medications and weight, height, BMI, fat-free mass
  • An important variable on REE measurement accuracy that should have been discussed is the time to achieve steady state.
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? ???
  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? ???
  7.5. Was the measurement of effect at an appropriate level of precision? ???
  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