Quick Links

  • Increase Font Size
  • Decrease Font Size
  • View as PDF

Recommendations Summary

EE: Application of Respiratory Quotient (RQ) in Critically Ill 2013

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)

    EE: RQ Within the Physiologic Range in Critically Ill

    If the respiratory quotient (RQ) falls within the physiologic range (0.67 to 1.3) the registered dietitian nutritionist (RDN) should not use RQ alone to reject the resting metabolic rate (RMR) measurement. Research shows that RQ can be manipulated within the physiologic range by changing respiratory parameters without altering the RMR measurement.

    Rating: Fair
    Imperative

    EE: RQ Outside the Physiologic Range in Critically Ill

    If the RQ falls outside the physiologic range (below 0.67 or greater than 1.3), the RDN should suspect an error and repeat the RMR measurement. The physiologic range of RQ reflecting cellular metabolism is 0.67 to 1.3. Values for RQ outside of this range indicate an inaccurate RMR measurement.

    Rating: Consensus
    Conditional

    EE: Limitations of RQ in Evaluating Feeding Levels in Critically Ill

    The RDN should not rely solely on measured RQ to evaluate level or composition of feeding. Research demonstrates that RQ has poor accuracy to evaluate under- and over-feeding. RQ can vary among individuals at any given feeding level and can be altered by factors unrelated to feeding.

    Rating: Strong
    Imperative

    • Risks/Harms of Implementing This Recommendation

      There are no potential risks or harms associated with the application of this recommendation.

    • Conditions of Application

      • The recommendation EE: RQ Outside Physiologic Range applies to RQ values below 0.67 or greater than 1.3 in critically ill patients
      • The RDN should use clinical judgment to determine if energy intake is in balance with the measured RMR, including calories from medication and IV fluids in the total energy intake calculation.

    • Potential Costs Associated with Application

      There are no obvious costs associated with the application of this recommendation.

    • Recommendation Narrative

      A total of eight studies were included in the evidence analysis for the EE: RQ Within the Physiologic Range in Critically Ill and EE: Limitations of RQ in Evaluating Feeding Levels in Critically Ill recommendations:

      • One positive-quality randomized controlled trial (RCT): Brandi et al, 1989
      • Three neutral-quality retrospective cohort studies: Guenst et al, 1994; Ireton-Jones and Turner, 1987; Kan et al, 2003
      • One neutral-quality RCT: Frankenfield et al, 1997
      • One neutral-quality cross-sectional study: McClave et al, 2003
      • One neutral-quality descriptive study: Weissman et al, 1986
      • One neutral-quality prospective cohort study: Zauner et al, 2001.

      EE: RQ Within the Physiologic Range in Critically Ill

      • One study provides limited evidence that RQ is affected by ventilator resetting and may remain within the physiologic range without altering the RMR measurement in the critically ill population
      • Additional research is needed regarding the accuracy of RQ to detect RMR measurement error in the critically ill population
      • Evidence is based on one study: Brandi et al, 1989.

      EE: RQ Outside the Physiologic Range in Critically Ill 

      No studies were included in the evidence analysis of this recommendation. However, four review articles provide support for the recommendation.

      • RQ, if not altered by respiratory or other artifact, varies according to the mix of fuels oxidized in the cells. The RQ range of individual fuels in human metabolism is 0.67 to 1.0. If fat synthesis is occurring, the RQ can rise to approximately 1.3. Humans never oxidize only one fuel. It therefore holds that an RQ range of 0.67 to 1.3 is the broadest range that can be ascribed to fuel metabolism and that an RQ below 0.67 or over 1.3 is related to something other than fuel metabolism and should be regarded as an error (e.g., protocol or equipment failure, respiratory artifact, severe acid-base disturbance) (Elia and Livesey, 1988, 1992).
      • A technical review stated that the range of physiological RQ is 0.67 to 1.3. An RQ of 0.67 would indicate ketone metabolism in a fasting state, while an RQ of 1.3 would indicate lipogenesis or a hyperventilated state. An RQ under 0.67 would suggest a leak in the indirect calorimetry device (da Rocha et al, 2006).
      • Sole metabolism of each macronutrient (i.e., carbohydrate, protein and fat) results in calculated RQs of 0.70, 0.80, and 1.0; respectively. However, conditions such as hypo- or hyperventilation, under- or overfeeding, acid/base imbalance, or ketone or ethanol metabolism could result in a physiological range for RQ of 0.67-1.3.  Measurements outside the range of 0.67-1.0 are nonphysiologic and should be considered an error due to inaccurate calibration, a leak in the calorimeter system, or some other artifact (McClave, 2003).

      EE: Limitations of RQ in Evaluating Feeding Levels in Critically Ill

      • Eight studies provide evidence that RQ has poor accuracy to evaluate under- and over-feeding
      • RQ can vary among individuals at any given feeding level and can be altered by factors unrelated to feeding
      • Evidence is based on the following: Brandi et al, 1989; Frankenfield et al, 1997; Guenst et al, 1994; Ireton-Jones and Turner, 1987; Kan et al, 2003; McClave et al, 2003; Weissman et al, 1986; and Zauner et al, 2001.

    • Recommendation Strength Rationale

      • Conclusion statements are Grade II
      • The recommendation EEU: RQ Outside the Physiologic Range in Critically Ill is consensus.

       

    • Minority Opinions

      None.