CI: Individual Equations (2010)

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To compare, under stable conditions, the Fick-calculated oxygen consumption with the indirect-calorimetry-derived oxygen consumption in a group of ventilated general surgical patients in the early postoperative period.
Inclusion Criteria:
Volume-controlled, ventilated general surgical patients in the post-operative period, undergoing major abdominal surgical procedures.
Exclusion Criteria:
  • Not hemodynamically stable
  • Required high doses of vasoactive medications
  • Required colloid solutions or packed RBC to maintain their perfusion pressure
  • Mechanically ventilated with pressure support ventilation and intermittent mandatory ventilation
  • Required an inspired oxygen concentration of more than 60%
  • Required positive end-expiratory pressure of more than 10 cm H2O
  • Had detectable air leaks anywhere in the circuit
  • Not adequately sedated and paralyzed 
Description of Study Protocol:


Methods not specified.


Cross-Sectional Study.

Blinding used (if applicable)

Not applicable.

Intervention (if applicable)

Oxygen consumption measured by indirect calorimetry and the Fick method.

Statistical Analysis

Normality of distribution was tested using Lillifors test.  Descriptive statistics, Pearson's product correlation coefficients, one-way ANOVA for repeated measures and Student t test, when appropriate, were completed.  The repeatability of cardiac output, arterial mixed venous oxygen content difference measurements, VO2 measured by the 2 methods and certain hemodynamic variables were determined by calculating the coefficient of variation of repeated measurements.  The bias and precision between techniques were analyzed by the Bland and Altman method.

Data Collection Summary:

Timing of Measurements

The study lasted 120 minutes.  In each patient, 9 serial measurements completed at 15 minute intervals.  All patients studied within 18 - 24 hours after a variety of procedures.

Dependent Variables

  • Oxygen consumption measured by indirect calorimetry, in the supine position, using Nellcor-Puritan-Bennett 7250 metabolic monitor, calibrated before each study period
  • Oxygen consumption as calculated by the Fick method using pulmonary artery catheter, with cardiac output measured by thermodilution 

Independent Variables

  • All studies performed at least 2 hours after any intervention or disturbance that would have altered the circulatory or ventilatory state of the patient
  • During the study period, any intervention or disturbance was avoided

Control Variables


Description of Actual Data Sample:

Initial N: 22 patients

Attrition (final N):  22 patients, male/female ratio not mentioned

Age:  mean age 71 +/- 8 years

Ethnicity:  not mentioned

Other relevant demographics:


Location:  Italy 


Summary of Results:

Other Findings

All comparisons between indirect calorimetry and Fick method were obtained during stable hemodynamic and respiratory conditions.

For 198 pairs of measurements, oxygen consumption as measured by the Fick method correlated significantly (y = 1.00x - 35.8, P = 0.0001, r = 0.77).

Oxygen consumption by indirect calorimetry was 212 +/- 32 ml/min (95% confidence interval:  207 - 216 ml/min) and by Fick was 177 +/- 41 ml/min (95% confidence interval:  171 - 183 ml/min)(P = 0.0001).

The bias (mean of the differences between indirect calorimetry and Fick method) was 35 +/- 26 ml/min (range -51 to 102 ml/min, 95% confidence interval:  31 - 39 ml/min) .  This difference represents 16 +/- 13% of the total body oxygen consumption and was highly significant (P = 0.0001).


Author Conclusion:
In conclusion, under controlled clinical conditions, VO2 calculated by the Fick method did not accurately predict VO2 measured by indirect calorimetry, and the 2 methods were not interchangeable.  VO2 calculated by the Fick method underestimated VO2 measured by indirect calorimetry by a systematic quantity that could be attributed to, in part, to VO2 of the lung.  Therefore, indirect calorimetry should be preferrred for the measurement of total body VO2 in mechanically ventilated surgical patients.
Funding Source:
Government: Italian Ministry of Univesity and Scientific Research
Reviewer Comments:
Recruitment methods and subjects not well defined.  Nutrition support not discussed.
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? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? ???
  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? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? ???
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
3. Were study groups comparable? N/A
  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? Yes
  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%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  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? N/A
  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? Yes
  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? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  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? Yes
  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? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  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? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? ???
  7.7. Were the measurements conducted consistently across groups? Yes
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? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  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)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  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? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes