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Recommendations Summary

CI: Steady State Measurement Conditions and Number of Measurements in a 24-Hour Period 2006

Click here to see the explanation of recommendation ratings (Strong, Fair, Weak, Consensus, Insufficient Evidence) and labels (Imperative or Conditional). To see more detail on the evidence from which the following recommendations were drawn, use the hyperlinks in the Supporting Evidence Section below.

  • Recommendation(s)

    CI: Steady State Measurement of RMR

    For ventilated patients, if a steady state is achieved, then a single measure is adequate to describe RMR. To achieve a steady state, discard the first five minutes of measurement. Then achieve a five-minute period with CV=5% for oxygen consumption and carbon dioxide production. An alternate protocol can be 25 minutes in duration if a CV of 10% is achieved. If proper attention is given to achieving resting conditions, 80% or more of RMR measures in ventilator patients will be in steady state. Sedation improves the likelihood of obtaining steady state measures.

    Rating: Strong

    CI: Non-steady state measurement conditions

    There are published data that were not in steady state, but were still reasonably close to steady state measures. When steady state is not achieved, interpret the results carefully. If the non-steady state conditions are chronic (e.g., patient posturing), then higher measures may reflect actual energy expenditure. If non-steady state conditions are episodic (e.g., ventilator change, nursing intervention, anxiety, coughing, sneezing, movement), RMR measures should be taken at a separate time.

    Rating: Consensus

    • Risks/Harms of Implementing This Recommendation

      No potential risks and harms are associated with the application of this recommendation.

    • Conditions of Application

      There are diseases and conditions that preclude an accurate indirect calorimetry measurement because a steady state cannot be reached or because of gas leaks:

      • Very high O2 requirement (fraction inspired oxygen greater than 80%)
      • Continuous positive airway pressure
      • Extra corporeal membrane oxygenation 
      • Air leaks (e.g.,  chest tube leak, cuff leak).

      With indirect calorimetry systems that measure both oxygen consumption and carbon dioxide production, both should be used to evalute steady state conditions.

    • Potential Costs Associated with Application

      If repeated measures are decided upon, then the cost is in time. 

    • Recommendation Narrative

      • To obtain accurate RMR measurement, attention must be given to assure steady state conditions defined by the degree of variation in vO2 and vCO2 over a set time period
      • Seventeen studies agree that steady state conditions minimize the chances that a short-term respiratory artifact will affect the measurement (five positive quality cohorts: Isbell et al, 1991; Gasic et al, 1997; Horner et al, 2001; Petros and Engelmann,  2001; McClave et al, 2003; six neutral quality cohorts: Van Lanschot et al,  1986; Leff et al,  1987; van Lanschot et al, 1988; Fredrix et al,  1990; Cunningham et al,  1994; Delikanaki-Skaribas, 2001; two negative quality cohorts: Schols et al,  1992; Stokes and Hill,  1992; one neutral quality non-randomized trial: Heymsfeld et al,  1987; one positive quality and two neutral quality repeat measures studies, respectively: Weststrate et al, 1989; Adriaens et al,  2003; Gibbons et al,  2004)
      • Two positive quality prospective cohort studies (Petros and Engelmann,  2001; McClave et al,  2003), one positive quality retrospective cohort (Frankenfield et al,  1996) and one neutral quality cohort (Cunningham et al,  1994) found that in critically ill ventilated patients, five-minute measures with <5% CV are equivalent to 30-minute measures with <10% CV
      • One positive quality non-randomized trial (Frankenfield et al,  1994) found that sedation has a significant positive impact on successfully achieving the steady state criteria
        • Resting metabolic rate in such patients is within 5% of TEE over 24 hours.
      • Two positive quality cohort studies (Isbell et al, 1991; Horner et al, 2001) found that for spontaneously breathing critically ill patients, the 10-minute steady state protocol (deleting the first five minutes) produces reliable RMR with minimal patient burden
      • Three positive quality cohort studies (Frankenfield et al, 1996; Petros and Engelmann, 2001; McClave et al, 2003) and one neutral quality cohort (Cunningham et al, 1994) found that for healthy individuals, residents of transitional care units and the critically ill, a single measurement (in steady state) is sufficient to describe RMR
      • For critically ill ventilated patients, if steady state is not achieved with the first measure, a second measurement should be obtained, according to one positive quality cohort study (Gasic et al, 1997) and one neutral quality cohort study (Cunningham et al, 1994)
      • One positive quality non-randomized trial (Frankenfield et al,  1994) found that a protocol-defining steady state at 5% CV over five consecutive minutes was successful in 80% of 24 ventilated critically ill patients and 74% attained steady state, defined as 10% CV over 30 minutes
        • When steady state was not attained, differences between the successful and failed measure were around 100kcal 80% to 90% of the time
        • Sedation improved the likelihood of obtaining steady state measures
        • The five-minute protocol required 10.5±1.3 (range, five to 27) minutes to complete, while the 30-minute protocol took 30.75±1.3 (range, 30 to 40) minutes.
      • A five-minute 5% CV steady state protocol was obtained successfully in 80% of 43 patients with assisted, in 100% of 43 with controlled ventilation and in 100% of 16 patients breathing room air, according to one positive quality cohort study (Petros and Engelmann,  2001)
        • Sedation improved the likelihood of obtaining steady state measures
        • The time (after deletion of the first five minutes) was 5.5±1.1 (range, five to 10) minutes to complete the five-minute protocol and 30.0±1.3 minutes in the longer protocol.
      • One neutral quality cohort study (Cunningham et al,  1994) found that in 46 critically ill mechanically ventilated patients, when the five-minute protocol was compared to a 30-minute protocol, the mean difference was -2.6±60kcal (R=0.983, P<0.0001)
        • To determine the minutes of measurement needed to determine RMR with no more than a 3% standard error of the mean in 95% of cases, a computer simulation suggested that with a 20% CV in vO2 and vCO2, a 25-minute measure was needed.

    • Recommendation Strength Rationale

      • Because a number of studies of positive quality were found to answer R.14.1 and essentially all agreed on the answer, the conclusion statement is Grade I
      • For R.14.2, two positive quality studies reported non-steady state measures, but no study set out to describe how to handle measures that did not meet steady state criteria
        • The interpretation is based on clinical experience of the indirect calorimetry panel.