Describe the clinical technique of bedside indirect calorimetry for the measurement of resting energy expenditure (REE) and respiratory quotient (RQ).
- “Steady state”-
- “Total daily energy expenditure” – includes basal metabolic rate (BMR), REE, dietary thermogenesis, and the caloric expenditure of voluntary physical activity.
- “BMR” the minimal heat production of an organism, measured from twelve to eighteen hours after the ingestion of food and with the organism at complete muscular rest. (Boothby & Sandiford, 1920)
- “Steady state or equilibration is a period of five or more consecutive 1-minute data points having a coefficient of variation for both oxygen consumption (VO2) and carbon dioxide production (VCO2) <5% (SD for each <5% of the respective mean) and an average resting minute ventilation that is appropriate for the patient’s size and clinical condition.”
- “Respiratory quotient” – same as the project definition.
No article inclusion criteria given
No article exclusion criteria given
Outcome(s) and other measures
- Summarized pertinent historical and current (e.g., up to 1985 articles)
No systematic search was completed; rather selection of articles based on authors’ experiences.
There were 33 references published dates from 1918 to 1984. Sample sizes represented by studies ranged from n=4 to n=239 (Harris Benedict) Chapters found within 3 books were cited as well as 1 letter to the editor.
Study participants represented acute care, oncology, and morbid obesity patients admitted into the hospital. The early, historical study by Harris-Benedict represented a healthy population.
The author cited most often was Askanazi J (n=4) followed by Feurer I (n=3).
COMPONENTS OF TOTAL DAILY ENERGY EXPENDITURE
Resting energy expenditure represents the major port (75-100%) of total daily energy expenditure.
Elwyn DH, Kinney JM, Askanazi J, 1981; Kinney JM, Long CL, Gump Fe et al, 1970
IC BASIC PRINCIPLESAll instruments consist of devices to measure the concentration of oxygen and carbon dioxide in a gas sample as well as the expire volume or low, temperature, barometric pressure, and time. In addition, data acquisition and analysis procedures must provide for serial reports at regular intervals.
“Measurement of gas exchange requires that mixed expired air is directed past gas analyzers. The concentration s of O2 and CO2 in the expired air are compared to the concentrations of O2 and CO2 in the inspired gas.. The exact composition of inspired air must be known or measured and room air must not be inadvertently mixed with the expired gas. The volume (or flow rate) of gas expired over a precise time period must be accurately measured.
- Key variables: Total expired volume of flow per unit time (e.g., minute ventilation; the fractional concentration of inspired oxygen (FIO2) and carbon dioxide (FICO2), the fractional concentration of mixed expired oxygen and carbon dioxide; barometric pressure; the temperature of mixed expired gas; and time.
Sterilization of accessory equipment
All equipment coming into contact with the patient’s skin, secretions and expired air must be sterilized or disposable. Adapters, mouthpieces, noseclips, and nonrebreathing valves should be washed and then steilized (ethylene oxide) after each use. Masks are scrubbed with a disinfecting solutin and all tubing used to direct expired air is replaced at regular intervals, depending on frequency and condition of use. The surfaces of the mixing chamber, canopy, and instrument are wiped down regularly with a disinfecting solution.
The volume measurement system, temperature sensor, and barometer are calibrated daily and gas analyzers are calibrated at the bedside before each measurement. Both 100% nitrogen and a calibration mixture (which approximates the composition of the patient’s mixed expired air, are used during the gas calibration procedures.
- Pt have rested in the supine position (in bed or a recliner) for >30 min before the measurement to avoid the effects of previous voluntary activity on REE.
- Pt are without oral dietary intake or intermittent enteral or parenteral feedings for >2 hr before REE to avoid the transient thermic effect of intermittent nutrient intake.
- Measurements are made in a quiet, thermoneutral environment
- The rate and composition of nutrients being infused on a continuous basis are noted.
- All sources of supplemental oxygen (e.g. nasal cannulas, masks, or tracheostomy collars)P are turned off during routine room air measurements.
- Pt have no voluntary skeletal muscle activity (movement of the extremities) during the measurement
- No leaks are present in the sampling system.
- All data used to derive the REE and RQ are taken from a period of equilibration or “steady state.”
Data Evaluation and Calculations
Our definition of equilibration is a period of five or more consecutive 1-minute data points having a coefficient of variation for both oxygen consumption (VO2) and carbon dioxide production (VCO2) <5% (SD for each <5% of the respective mean) and an average resting minute ventilation that is appropriate for the patient’s size and clinical condition.
“In our experience if a patient does not equilibrate within the first 15 min of gas collection time, he or she is unlikely to do so.”
The abbreviated Weir formula: (same as project definition). The difference between REE derived via the abbreviated formula versus complete equation is less than 2%
Weir JB, 1949, Wilmore DW 1977 (book citation)
Measurements of the whole body RQ reflect net substrate oxidation at the time of measurement (e.g., CHO oxidation net RQ = 1.0; “Mixed substrate” oxidation RQ=0.85; Fat oxidation RQ=0.70; Lipogenesis RQ =1.00-1.20; and non-steady state hyperventilation RQ=>1.00.
Additional Useful Patient Data
- Measured, calculated, and clinical data that are noted at the time of REE include:
- Weight Current, usual, and ideal body weight
- (None reported)
- Primary diagnosis and relevant secondary diagnosis
- Vital signs
- Recent operative procedures
- General assessment of pts daily level of activity
- Gas collection technique used
- FIO2 if pt is being mechanically ventilated
- No. hrs since most recent intermitten nutrient intake
- Composition and rate of any continuous feedings
- Measured RE expressed as a % Harris-Benedict standard
- IC taken in a fasting state.
GAS COLLECTION SYSTEM SPECIFICSThose patients who cannot tolerate 15 minutes without enriched oxygen cannot be tested. Conditions that prohibit the complete collection of expired air such as the presence of chest tubes with documented air leaks or deflated endotracheal cannula cuffs also preclude measurement of REE.
Mouthpiece and noseclip system – For short-term measurements (<15 mins) on patients breathing room air, mouthpiece, noseclip and non-rebreathng valve system.
Mask- Used for short-term mesurement if the patient cannot use the mouthpiece system, providing that extreme care is taken to ensure a complete seal at the mask cuff throughout the measurement. Under no circumstances should the patient hold the mask in place. Masks may not be used when nasoenteric tubing is present.
Ventilator- the FIO2 delivered to the patient must be stable and accurately measured. Frequently, the internal blending system of the ventilator is not sufficiently consistent for the precision required during metabolic measurements and as FIO2 icreases, the magnitude of error associated with unstable or inaccurately measured FIO2 also increases.
Browning JA, Linberg SE et al, 1982
Canopy System- The rate of flow through the canopy is adjusted to maintain the FCO2 in the canopy between 0.0065 and 0.0085 and the canopy air is directed to the mixing chamber. Std metabolic variables are then derived from the concentration differences between inspired and expired Ox and CO2 and the measured flow rate.
Precautions should be taken to ensure that patients do not fall asleep and do not speak during the test as the former will result in a falsely low measurement and the latter will elevate the concentration of CO2 in the canopy and preclude equilibration.
If a measurement does not reach equilibrium, or data are physiologically unreasonable, the operator should:
- Ascertain that the pt is rested and comfortable but not sleeping
- Check for leaks at any point in the external sampling system b/t the patient and the collection chamber
- Make sure that sources of supplemental oxygen have been turned off during room air measurements
- Check for interruptions in the internal sampling pathway
- Check gas calibration
- RE-evaluate FIO2 stability and sampling accuracy during ventilator measurements.
As stated by the author in body of report
- “There exists significant individual variability in measured REE (percent standard) in a variety of malnourished or nutritionally at risk hospitalized patient populations. When measured according to a strict protocol, REE eliminates the guesswork in estimating the combined effects of body composition, nutrition status, disease processes, trauma, and clinical events on metabolic rate in patients requiring specialized nutrition/metabolic assessment, monitoring and/or support.
|University/Hospital:||University of Pennsylvania|
- The strength of this review is that the authors define the process that has been followed in the clinic setting over the past 20+ years. While many of the dated references cited are valid in today’s clinical setting, the machine calibration and use of IC with ventilators is outdated. Other areas, such as RQ and measurement length are being challenged. In addition, these guidelines do not address healthy population concerns.
- With regards to nutrition parameters, use of “ideal body weight” is an outdated mode, especially considering an obese population. Use of HB, while historically a nutrition assessment standard, needs re-evaluation.
Quality Criteria Checklist: Review Articles
|1.||Will the answer if true, have a direct bearing on the health of patients?||Yes|
|2.||Is the outcome or topic something that patients/clients/population groups would care about?||Yes|
|3.||Is the problem addressed in the review one that is relevant to dietetics practice?||Yes|
|4.||Will the information, if true, require a change in practice?||Yes|
|1.||Was the question for the review clearly focused and appropriate?||Yes|
|2.||Was the search strategy used to locate relevant studies comprehensive? Were the databases searched and the search termsused described?||No|
|3.||Were explicit methods used to select studies to include in the review? Were inclusion/exclusion criteria specified andappropriate? Wereselectionmethods unbiased?||No|
|4.||Was there an appraisal of the quality and validity of studies included in the review? Were appraisal methodsspecified,appropriate, andreproducible?||No|
|5.||Were specific treatments/interventions/exposures described? Were treatments similar enough to be combined?||Yes|
|6.||Was the outcome of interest clearly indicated? Were other potential harms and benefits considered?||Yes|
|7.||Were processes for data abstraction, synthesis, and analysis described? Were they applied consistently acrossstudies and groups? Was thereappropriate use of qualitative and/or quantitative synthesis? Was variation in findings among studies analyzed? Were heterogeneity issued considered? If data from studies were aggregated for meta-analysis, was the procedure described?||No|
|8.||Are the results clearly presented in narrative and/or quantitative terms? If summary statistics are used, are levels ofsignificance and/or confidence intervals included?||Yes|
|9.||Are conclusions supported by results with biases and limitations taken into consideration? Are limitations ofthe review identified anddiscussed?||???|
|10.||Was bias due to the review's funding or sponsorship unlikely?||Yes|