EE: Respiratory Quotient (RQ) (2013)

Citation:

Guenst IM, Nelson LD. Predictors of parenteral nutrition-induced lipogenesis. Chest. 1994;105(2):553-559.

 
Study Design:
Retrospective Cohort Study
Class:
B - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
  1. To determine the incidence and causes for net fat synthesis during total Parenteral nutrition (TPN) in critically ill, mechanically ventilated patients.      
  2. To suggest means by which caloric intake in this patient population may be optimized.

Abbreviations

  • BSA: body surface area
  • IMV: intermittent mandatory ventilation rate (breath per min)
  • TV: total volume
  • MV: minute ventilation
Inclusion Criteria:
  1. Understand and give written consent
  2. Patients who had difficulty in weaning from mechanical ventilatory support as manifested by high minute ventilation and/or carbon dioxide retention were studied.

Note

  • ”No specific groups of patients were selected and no randomization was used to decide which patients would be studied.”
Exclusion Criteria:
  1. Refusal to consent
  2. Not meeting inclusion criteria
Description of Study Protocol:

A retrospective patients review

Indirect calorimetry was used to determine patient’s measured energy expenditure (MEE) and respiratory quotient (RQ). Additionally, total caloric intake (TCAL), glucose intolerance rate, basal energy expenditure (BEE), estimated stress factor, and calculated energy expenditure (CEE) were assessed in each patient.

Resting energy expenditure

  • IC type: Metabolic Gas Monitor-MGM/TWO
  • Equipment of Calibration: Yes
  • Coefficient of variation using std gases: not specified
  • Rest before measure (state length of time rested if available):
  • Fasting: No on TPN for 24-48 h after reached estimated target
  • Exercise restrictions: NA
  • Room temp: Hospital air
  • Measurement length: 30 min.
  • # of measures: 1
  • Were some measures eliminated: Yes, non-steady state
  • Steady state: MEE, VO2 VCO2and RQ were recorded on reaching steady state. (Steady state was not defined in the article)
  • Were some measures averaged: Likely
  • Training of measurer: Likely
  • Subject training: No

DIETARY

  • All patients were assessed by nutrition support team prior to the metabolic measurement.
  • Recommendation regarding to total caloric intake (TCAL) were made using Harris-Benedict calculation on BEE times an estimated stress factor based on severity of illness and activity.
  • Amino acid administration was calculated to achieve positive nitrogen balance.
  • The standard hospital central venous formulation was 4.25 % AA, supplements up to 7.5% AA were available.
  • Dextrose concentration was generally 25% but range from 5% to 25%
  • Fat emulsions were given as 10% and 20% solutions administered over 6 to 8 h, twice per wk.
Data Collection Summary:

Substrate administration, age, sex, Ht, Wt, urine urea nitrogen, ventilatory support level, acid-base balance, oxygen consumption, carbon dioxide production, RQ, and MEE were recorded.

Blinding used: not applicable

Description of Actual Data Sample:
  • N=140
  • RQ=1 n=74
  • RQ>1 n=66

Statistical tests

  • Student’s t test for unpaired data was used to determinations of differences in mean values between subgroups.
  • A paired t test was used to compare mean values of data on patients within subgroups
  • Correlation between values was assessed by linear regression analysis
  • Fisher’s exact test was used to compare ratios of nonparametric data.
Summary of Results:

Physical data and ventilatory support

RQ=1 RQ>1 p
No. 74 66

Age

66±14 65±14 NS

Ht(cm)

169.2±8.6 168.1±9.9 NS

Wt(kg)

69.3±15.8 72.6±14.3<0.05

BSA

1.79±0.21 1.83±0.2 <0.05

FIO2

.40±0.08 0.40±0.08 NS

IMV rate

9.9±5.0 11.0±8.4 NS

TV

904±146 860±130 NS

Total MV

11.5±4.5 13.5±5.3 <0.05

47% of patients had RQ>1, indicating net fat synthesis. Their caloric intake was statistically greater than their actual energy expenditure (MEE).

Statistically significant differences in oxygen consumption, CO2production, measured energy expenditure, total and carbohydrate caloric intake, and glucose infusion rate were found between groups of patients with an RQ =1 or >1.

73% of patients with glucose infusion rate >4 mg/kg-min had RQs >1.

A moderate correlation exists between RQ and the TCAL/MEE ratio (r=0.54, p<0.001, y=0.83+0.16x). When the total calories delivered equals the MEE, the predicted value of RQ is 0.99.

A moderate correlation exist (r=0.55, p<0.001) between glucose infusion rate and RQ. A glucose infusion rate of 4 mg/kg-min (actual body wt) corresponds to a predicted RQ of 1.04.

Author Conclusion:

“Net fat synthesis was found in a surprisingly large number of critically ill patients receiving central venous nutrition. Many of these patients received carbohydrate calories in excess of their measured energy expenditure, even though it appeared that they need this level of caloric intake by clinical assessment.”

“The high carbohydrate total Parenteral nutrition solutions with lipids provided only for prevention of essential fatty acid depletion resulted in an unacceptably high incidence of fat synthesis.”

“The results suggest that caloric intake may be optimized in critically ill patients using indirect calorimetry.”

“When calorimetry is not available a total caloric intake of up to 140% of the BEE with glucose infusion rate not exceeding 4 mg/kg-min and fats providing 40-60 % of calories will meet the energy requirements of most critically ill patients without forcing the RQ>1.”
Funding Source:
University/Hospital: Vanderbilt University Nashville TN
Reviewer Comments:

Strengths 

  • Appropriate statistical analysis.

Generalizability/Weaknesses

  • Large sample size with a mixture of population. 2 subgroups were assessed with comparability. Greater generalizability. Could be apply to critically ill patients.
  • Limitations were not fully discussed.
  • Retrospective cohort---only deterined the association between variables but not the cause and effect.
  • Suggestion of using IC testing for assessing caloric needs were based on authors’ opinion, but by the evidence at current study.
[Expert Panel member note: This is a retrospective study that mentions steady state, but they do not define it. It is also stated that measurements were made during a time “representative of the patient’s overall activity,” which gives indication of uncontrolled conditions. Three RQ measures were >1 in patients receiving calories at only 20-40% of measured expenditure, which in a retrospective chart review is suspicious for the presence of artifacts in this study.]
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? No
  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? No
  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? No
  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