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## Complete Summary

#### GUIDELINE TITLE

Metabolic measurement using indirect calorimetry during mechanical
ventilation --- 2004 revision & update.

#### BIBLIOGRAPHIC SOURCE(S)

American Association for Respiratory Care. Metabolic measurement using
indirect calorimetry during mechanical ventilation\--2004 revision &
update. Respir Care 2004 Sep;49(9):1073-9. \[84 references\]

#### GUIDELINE STATUS

This is the current release of the guideline.

This guideline updates a previous version: American Association for
Respiratory Care (AARC). AARC clinical practice guideline. Metabolic
measurement using indirect calorimetry during mechanical ventilation.
Respir Care 1994 Dec;39(12):1170-5.

### COMPLETE SUMMARY CONTENT

 SCOPE\
 METHODOLOGY - including Rating Scheme and Cost Analysis\
 RECOMMENDATIONS\
 EVIDENCE SUPPORTING THE RECOMMENDATIONS\
 BENEFITS/HARMS OF IMPLEMENTING THE GUIDELINE RECOMMENDATIONS\
 CONTRAINDICATIONS\
 QUALIFYING STATEMENTS\
 IMPLEMENTATION OF THE GUIDELINE\
 INSTITUTE OF MEDICINE (IOM) NATIONAL HEALTHCARE QUALITY REPORT
CATEGORIES\
 IDENTIFYING INFORMATION AND AVAILABILITY\
 DISCLAIMER

### SCOPE

#### DISEASE/CONDITION(S)

-   Pulmonary disease

-   Nutritional risk, deficit, or derangement

#### GUIDELINE CATEGORY

Assessment of Therapeutic Effectiveness

#### CLINICAL SPECIALTY

Nutrition\
Pediatrics\
Pulmonary Medicine

#### INTENDED USERS

Respiratory Care Practitioners

#### GUIDELINE OBJECTIVE(S)

-   To improve the consistency and appropriateness of respiratory care
    and serve as a guide for education and research

-   To provide clinical practice guidelines addressing metabolic
    measurement during mechanical ventilation

#### TARGET POPULATION

Mechanically ventilated neonatal, pediatric, and adult patients in the
hospital or in extended care facilities

#### INTERVENTIONS AND PRACTICES CONSIDERED

Metabolic measurements using indirect calorimetry for determination of
oxygen consumption (V~O2~), carbon dioxide production (V~CO2~),
respiratory quotient (RQ), and resting energy expenditure (REE)

#### MAJOR OUTCOMES CONSIDERED

-   Resting energy expenditure (REE) measurements

-   Incidence of overfeeding and underfeeding

-   Costs associated with total parenteral nutrition

### METHODOLOGY

#### METHODS USED TO COLLECT/SELECT EVIDENCE

Searches of Electronic Databases

#### DESCRIPTION OF METHODS USED TO COLLECT/SELECT THE EVIDENCE

Not stated

#### NUMBER OF SOURCE DOCUMENTS

Not stated

#### METHODS USED TO ASSESS THE QUALITY AND STRENGTH OF THE EVIDENCE

Not stated

#### RATING SCHEME FOR THE STRENGTH OF THE EVIDENCE

Not applicable

#### METHODS USED TO ANALYZE THE EVIDENCE

Systematic Review

#### DESCRIPTION OF THE METHODS USED TO ANALYZE THE EVIDENCE

Not stated

#### METHODS USED TO FORMULATE THE RECOMMENDATIONS

Not stated

#### RATING SCHEME FOR THE STRENGTH OF THE RECOMMENDATIONS

Not applicable

#### COST ANALYSIS

A formal cost analysis was not performed and published cost analyses
were not reviewed.

#### METHOD OF GUIDELINE VALIDATION

External Peer Review\
Internal Peer Review

#### DESCRIPTION OF METHOD OF GUIDELINE VALIDATION

Consultants to the Working Group may review the initial draft of the
guideline. After completion by the Working Group, the draft is reviewed
by the entire Steering Committee and then by a Review Panel (i.e.,
persons engaged in all facets of the delivery of respiratory care who
have volunteered to review drafts of the Guidelines before publication).

This update was approved by the 2003 Clinical Practice Guideline (CPG)
Steering Committee.

### RECOMMENDATIONS

#### MAJOR RECOMMENDATIONS

**Procedure**

Metabolic measurements using indirect calorimetry for determination of
oxygen consumption (V~O2~), carbon dioxide production (V~CO2~),
respiratory quotient (RQ), and resting energy expenditure (REE) as an
aid to patient nutritional assessment and management; assessment of
weaning success and outcome; assessment of the relationship between O~2~
delivery (D~O2~) and V~O2~; and assessment of the contribution of
metabolism to ventilation. The guideline addresses metabolic measurement
during mechanical ventilation.

**Description/Definition**

Metabolic measurements use an indirect calorimeter to measure V~O2~ and
V~CO2~ via expired gas analysis. The measurements of V~O2~ and V~CO2~
are used to calculate RQ (V~CO2~/V~O2~) and REE using the Weir equation:

REE = \[V~O2~ (3.941) + V~CO2~ (1.11)\] 1440 min/day

The measurement of REE in mechanically ventilated neonatal, pediatric,
and adult patients has been shown to be more accurate than published
formulas used to predict REE, to reduce the incidence of overfeeding and
underfeeding, and to decrease costs associated with total parenteral
nutrition (TPN). Measurement of REE and RQ has been shown to be helpful
in designing nutritional regimens to reduce V~CO2~ in patients with
chronic obstructive pulmonary disease (COPD) and patients requiring
mechanical ventilation. Despite this evidence, studies demonstrating
improved outcome, decreased time spent on the ventilator, or shorter
intensive care unit (ICU)/hospital stay are lacking.

The objectives of metabolic measurements by indirect calorimetry are:

-   To accurately determine the REE of mechanically ventilated patients
    to guide appropriate nutritional support

-   To accurately determine RQ to allow nutritional regimens to be
    tailored to patient needs

-   To accurately determine REE and RQ to monitor the adequacy and
    appropriateness of current nutritional support

-   To allow determination of substrate utilization when urinary
    nitrogen values are concomitantly measured

-   To determine the O~2~ cost of breathing as a guide to the selection
    of ventilator mode, settings, and weaning strategies

-   To monitor the V~O2~ as a guide to targeting adequate D~O2~

-   To assess the contribution of metabolism to ventilation

**Setting**

-   Mechanically ventilated patients

    -   In the hospital

    -   In the extended care facility

**Indications**

Metabolic measurements may be indicated:

-   In patients with known nutritional deficits or derangements.
    Multiple nutritional risk and stress factors that may considerably
    skew prediction by Harris-Benedict equation include:

    -   Neurologic trauma

    -   Paralysis

    -   COPD

    -   Acute pancreatitis

    -   Cancer with residual tumor burden

    -   Multiple trauma

    -   Amputations

    -   Patients in whom height and weight cannot be accurately obtained

    -   Patients who fail to respond adequately to estimated nutritional
        needs

    -   Patients who require long-term acute care

    -   Severe sepsis

    -   Extremely obese patients

    -   Severely hypermetabolic or hypometabolic patients

-   When patients fail attempts at liberation from mechanical
    ventilation to measure the O~2~ cost of breathing and the components
    of ventilation

-   When the need exists to assess the V~O2~ in order to evaluate the
    hemodynamic support of mechanically ventilated patients

-   To measure cardiac output by the Fick method

-   To determine the cause(s) of increased ventilatory requirements

**Contraindications**

Refer to the \"Contraindications\" field or see the original guideline
document.

**Hazards/Complications**

Refer to the \"Potential Harms\" field or see the original guideline
document.

**Limitations of Procedure**

Limitations of the procedure include:

-   Accurate assessment of REE and RQ may not be possible because of
    patient condition or certain bedside procedures or activities.

-   Inaccurate measurement of REE and RQ may be caused by leaks of gas
    from the patient/ventilator system preventing collection of expired
    gases including:

    -   Leaks in the ventilator circuit

    -   Leaks around tracheal tube cuffs or uncuffed tubes

    -   Leaks through chest tubes or bronchopleural fistula

-   Inaccurate measurement of REE and RQ occurs during peritoneal and
    hemodialysis due to removal across the membrane of CO~2~ that is not
    measured by the indirect calorimeter.

-   Inaccurate measurement of REE and RQ during open circuit measurement
    may be caused by:

    -   Instability of delivered oxygen concentration (F~IO2~) within a
        breath or breath to breath due to changes in source gas pressure
        and ventilator blender/mixing characteristics

    -   F~IO2~ \>0.60

    -   Inability to separate inspired and expired gases due to bias
        flow from flow-triggering systems, IMV systems, or specific
        ventilator characteristics

    -   The presence of anesthetic gases or gases other than O~2~,
        CO~2~, and nitrogen in the ventilation system

    -   The presence of water vapor resulting in sensor malfunction

    -   Inappropriate calibration

    -   Connection of the indirect calorimeter to certain ventilators,
        with adverse effect on triggering mechanism, increased
        expiratory resistance, pressure measurement, or maintenance of
        the ventilator

    -   Total circuit flow exceeding internal gas flow of indirect
        calorimeter that incorporates the dilutional principle

    -   Internal leaks within the calorimeter

    -   Inadequate length of measurement

-   Inaccurate measurement of REE and RQ during closed circuit
    measurement may be caused by:

    -   Short duration of the measurement period (a function of CO~2~
        absorber life and V~CO2~) that may not allow REE state to be
        achieved

    -   Changes in functional residual capacity (FRC) resulting in
        changes in spirometer volume unassociated with V~O2~

    -   Leaks drawing gas into the system during spontaneous breathing
        measurements that adds volume to the system and cause
        erroneously low V~O2~ readings

    -   Increased compressible volume in the circuit that prevents
        adequate tidal volume delivery resulting in alveolar
        hypoventilation and changes in V~CO2~/V~O2~

    -   Increased compressible volume and resistance that results in
        difficulty triggering the ventilator and increased work of
        breathing

**Assessment of Need**

Metabolic measurements should be performed only on the order of a
physician after review of indications (see \"Indications\" section
above) and objectives.

**Assessment of Test Quality and Outcome**

Test quality can be evaluated by determining whether:

-   RQ is consistent with the patient\'s nutritional intake

-   RQ rests in the normal physiologic range (0.67 to 1.3)

-   Variability of the measurements for V~O2~ and V~CO2~ should be
    [\<]{.underline}5% for a 5-minute data collection

-   The measurement is of sufficient length to account for variability
    in V~O2~ and V~CO2~ if the above conditions ([\<]{.underline}5% for
    a 5-minute data collection) are not met

Outcome may be assessed by comparing the measurement results with the
patient\'s condition and nutritional intake.

Outcome may be assessed by observation of the patient prior to and
during the measurement to determine if the patient is at steady state.

**Resources**

Indirect calorimeter, open- or closed-circuit design:

-   The calibration gas mixture should be relevant to the concentration
    of gas to be measured clinically.

-   The indirect calorimeter should be calibrated on the day of
    measurement and more often if errors in measurement are suspected.

-   When the measurement results are suspect and/or when repeated
    calibration attempts are marked by instability, the indirect
    calorimeter may be tested via an independent test method (burning
    ethanol or other substance with a known RQ or adding known flows of
    CO~2~ and nitrogen to simulate V~O2~ and V~CO2~). As a simple test,
    ventilation of a leak-free system should yield V~O2~ and V~CO2~
    values of near 0. Routinely scheduled measurement of normal control
    subjects (volunteers) may be useful.

A method of stabilizing F~IO2~ during open-circuit measurements should
be available and may include:

-   An air-oxygen blender connected between the gas source and the
    ventilator inlets for high pressure gas

-   An inspiratory mixing chamber between the ventilator main flow
    circuit and the humidifier (see \"Hazards/Complications\" in
    \"Potential Harms\" field or refer to original guideline document)

-   Ventilator changes, which may include mode, inspiratory flow rate,
    positive end-expiratory pressure (PEEP), or tidal volume to improve
    patient-ventilator synchrony

An isolation valve, double-piloted exhalation valve, or other device to
separate inspiratory and expiratory flow should be incorporated when
using continuous flow in the ventilator circuit (see
\"Hazards/Complications\" in \"Potential Harms\" field or refer to
original guideline document).

Personnel: Due to the level of technical and patient assessment skills
required, metabolic measurements using indirect calorimeters should be
performed by individuals trained in and with the demonstrated and
documented ability to:

-   Calibrate, operate, and maintain an indirect calorimeter

-   Operate a mechanical ventilator, including knowledge of the
    air-oxygen blending system, the spontaneous breathing mechanisms,
    and the alarm and monitoring functions

-   Recognize metabolic measurement values within the normal physiologic
    range and evaluate the results in light of the patient\'s current
    nutritional and clinical status

-   Assess patient hemodynamic and ventilatory status and make
    recommendations on appropriate corrective/therapeutic maneuvers to
    improve or reverse the patient\'s clinical course. A relevant
    credential (e.g., RRT, CRT, RN, or RPFT) is desirable.

A hood canopy system in combination with airway sampling may be employed
to capture gas that leaks around an uncuffed endotracheal tube.

If a stable F~IO2~ cannot be achieved, V~CO2~ may be used to estimate
REE by assuming an RQ of 0.83 and the largest expected error is an:

-   Underestimation of 25% for RQ of 1.2

-   Overestimation of 19% for RQ of 0.67

A simultaneous measure of P~aCO2~ and V~CO2~ will allow calculation of
pulmonary dead space and components of ventilation using the Bohr
equation:

V~E~ = V~CO2~ x 0.863 P~aCO2~ x (1-V~D~/V~T~)

**Monitoring**

The following should be evaluated during the performance of a metabolic
measurement to ascertain the validity of the results:

-   Clinical observation of the resting state (see \"Assessment of Test
    Quality and Outcome\" section above)

-   Patient comfort and movement during testing

-   Values in concert with the clinical situation

-   Equipment function

-   Results within the specifications listed in \"Assessment of Test
    Quality and Outcome\" section above

-   F~IO2~ stability

Measurement data should include a statement of test quality and list the
current nutritional support, ventilator settings, F~IO2~ stability, and
vital signs.

**Frequency**

Metabolic measurements should be repeated according to the clinical
status of the patient and indications for performing the test. The
literature suggests that more frequent measurement may be necessary in
patients with a rapidly changing clinical course as recognized by:

-   Hemodynamic instability

-   Spiking fevers

Patients in the immediate postoperative period and those being weaned
from mechanical ventilation may also need more frequent measurement.

**Infection Control**

Metabolic measurements using indirect calorimetry are relatively safe
procedures, but a remote possibility of cross-contamination exists
either via patient-patient or patient-caregiver interface. The following
guidelines should be followed when a metabolic measurement is performed.

-   Standard Precautions should be exercised whenever there is potential
    for contamination with blood or other body fluids.

-   Appropriate use of barriers and hand washing is recommended.

-   Tubing used to direct expiratory gas from the ventilator to the
    indirect calorimeter should be disposed of or cleaned between
    patients.

-   Connections used in the inspiratory limb of the circuit proximal to
    the humidifier should be wiped clean between patients; equipment
    distal to the humidifier should be disposed of or subjected to
    high-level disinfection between patients.

-   Bacteria filters may be used to protect equipment in both the
    inspired and expired lines, but caution should be used that moisture
    does not increase filter resistance resulting in poor gas sampling
    flow or increased resistance to exhalation.

#### CLINICAL ALGORITHM(S)

None provided

### EVIDENCE SUPPORTING THE RECOMMENDATIONS

#### TYPE OF EVIDENCE SUPPORTING THE RECOMMENDATIONS

The type of supporting evidence is not specifically stated for each
recommendation.

### BENEFITS/HARMS OF IMPLEMENTING THE GUIDELINE RECOMMENDATIONS

#### POTENTIAL BENEFITS

-   Accurate metabolic measurement during mechanical ventilation

-   Improved nutritional support for mechanically ventilated patients

#### POTENTIAL HARMS

Performing metabolic measurements using an indirect calorimeter is a
safe, noninvasive procedure with few hazards or complications. Under
certain circumstances and with particular equipment the following
hazards/complications may be seen.

-   Closed circuit calorimeters may cause a reduction in alveolar
    ventilation due to increased compressible volume of the breathing
    circuit.

-   Closed circuit calorimeters may decrease the trigger sensitivity of
    the ventilator and result in increased patient work of breathing.

-   Short-term disconnection of the patient from the ventilator for
    connection of the indirect calorimetry apparatus may result in
    hypoxemia, bradycardia, and patient discomfort.

-   Inappropriate calibration or system setup may result in erroneous
    results causing incorrect patient management.

-   Isolation valves may increase circuit resistance and cause increased
    work of breathing and/or dynamic hyperinflation.

-   Inspiratory reservoirs may cause a reduction in alveolar ventilation
    due to increased compressible volume of the breathing circuit.

-   Manipulation of the ventilator circuit may cause leaks that may
    lower alveolar ventilation.

### CONTRAINDICATIONS

#### CONTRAINDICATIONS

When a specific indication is present, there are no contraindications to
performing a metabolic measurement using indirect calorimetry unless
short-term disconnection of ventilatory support for connection of
measurement lines results in hypoxemia, bradycardia, or other adverse
effects.

### QUALIFYING STATEMENTS

#### QUALIFYING STATEMENTS

The measurement of resting energy expenditure (REE) in mechanically
ventilated neonatal, pediatric, and adult patients has been shown to be
more accurate than published formulas used to predict REE, to reduce the
incidence of overfeeding and underfeeding, and to decrease costs
associated with total parenteral nutrition (TPN). Measurement of REE and
respiratory quotients (RQ) has been shown to be helpful in designing
nutritional regimens to reduce carbon dioxide production (V~CO2~) in
patients with chronic obstructive pulmonary disease (COPD) and patients
requiring mechanical ventilation. Despite this evidence, studies
demonstrating improved outcome, decreased time spent on the ventilator,
or shorter intensive care unit/hospital stay are lacking.

### IMPLEMENTATION OF THE GUIDELINE

#### DESCRIPTION OF IMPLEMENTATION STRATEGY

An implementation strategy was not provided.

### INSTITUTE OF MEDICINE (IOM) NATIONAL HEALTHCARE QUALITY REPORT CATEGORIES

#### IOM CARE NEED

Getting Better\
Living with Illness

#### IOM DOMAIN

Effectiveness\
Safety

### IDENTIFYING INFORMATION AND AVAILABILITY

#### BIBLIOGRAPHIC SOURCE(S)

American Association for Respiratory Care. Metabolic measurement using
indirect calorimetry during mechanical ventilation\--2004 revision &
update. Respir Care 2004 Sep;49(9):1073-9. \[84 references\]

#### ADAPTATION

Not applicable: The guideline was not adapted from another source.

#### DATE RELEASED

1994 Dec (revised 2004 Sep)

#### GUIDELINE DEVELOPER(S)

American Association for Respiratory Care - Professional Association

#### SOURCE(S) OF FUNDING

American Association for Respiratory Care (AARC)

#### GUIDELINE COMMITTEE

Not stated

#### COMPOSITION OF GROUP THAT AUTHORED THE GUIDELINE

*Primary Author*: Charles D. McArthur, RRT, RPFT, Immanuel St
Joseph\'s - Mayo Health System, Mankato, Minnesota

#### FINANCIAL DISCLOSURES/CONFLICTS OF INTEREST

Not stated

#### GUIDELINE STATUS

This is the current release of the guideline.

This guideline updates a previous version: American Association for
Respiratory Care (AARC). AARC clinical practice guideline. Metabolic
measurement using indirect calorimetry during mechanical ventilation.
Respir Care 1994 Dec;39(12):1170-5.

#### GUIDELINE AVAILABILITY

Electronic copies: Available in Portable Document Format (PDF) from the
[American Association for Respiratory Care (AARC) Web
site](http://www.rcjournal.com/contents/09.04/09.04.1073.pdf).

Print copies: Available from the American Association for Respiratory
Care (AARC), CPG Desk, 11030 Ables Ln, Dallas, TX 75229-4593; Web site:
[www.aarc.org](http://www.aarc.org/).

#### AVAILABILITY OF COMPANION DOCUMENTS

None available

#### PATIENT RESOURCES

None available

#### NGC STATUS

This summary was completed by ECRI on November 30, 1998. The information
was verified by the guideline developer on December 15, 1998. This NGC
summary was updated by ECRI on March 22, 2005.

#### COPYRIGHT STATEMENT

This NGC summary is based on the original guideline, which is subject to
the guideline developer\'s copyright restrictions.

### DISCLAIMER

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© 1998-2008 National Guideline Clearinghouse

Date Modified: 11/3/2008