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Recommendations Summary

CI: Impact of Thermic Effect of Feeding on RMR 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: Thermic effect of continuous feeding on RMR

    If a critically ill patient is continuously receiving any energy source (e.g., intravenous fluids, EN or PN), the rate and concentration should remain unchanged during the 24-hour period before and during RMR measure. After 24-hour equilibration, the impact of the TEF on RMR is constant and indirect calorimetry measurements can proceed.

    Rating: Fair

    CI: Thermic effect of intermittent feeding on RMR

    If a critically ill patient receives intermittent EN above 400kcal per feeding, then hold feedings for a minimum of five hours before measuring RMR. When a five-hour fast is not clinically feasible or when a small feeding (<400kcal) is given, a four-hour fast is allowed. Measuring RMR during the time of the TEF will produce inaccurately high values.

    Rating: Weak

    • Risks/Harms of Implementing This Recommendation

      • Patients with severe malnutrition risk inadequate nutritional repletion by long fasts
      • Patients with IDDM risk hypoglycemia with longer fasts.

    • Conditions of Application

      • In continuously fed patients, the TEF is constant and can be considered part of the resting state 
      • By contrast with intermittent feeding, there is a peak in TEF that will be higher than resting measures 
        • There is a variable increase in non-resting level that will produce artificially high RMR and indirect calorimetry measurement should be delayed until fasting conditions are met.
      • Critical care patients with severe malnutrition may need more feedings than a five-hour fast will accommodate
      • Critical care patients with IDDM may not be appropriate for a five-hour fast
      • Thus, a four-hour fast after a small meal (400kcal or less) is permitted
      • Challenges to implementation: Scheduling of measurements within these parameters may be difficult for individual patients.

    • Potential Costs Associated with Application

      No obvious costs are associated with the application of this recommendation.

    • Recommendation Narrative

      • Three positive quality repeat-measures crossover studies [Kinabo and Durnin,  1990 (men); Kinabo and Durnin, 1990 (women); Levine et al,  2000] and two neutral quality studies (Bissoli et al,  1999; Raben et al,  2003) confirmed that the peak in TEF occurs between 60 and 180 minutes in most individuals, with people who are older and obese tending to peak later than non-obese and younger people 
        • Total TEF is approximately 7% to 9% of kcals consumed after meals of 400kcal to 1, 200kcal in subjects who are non-obese and obese  
        • Thus, small meals will have lower TEF.
      • A neutral quality meta-analysis of a series of studies in one laboratory (Reed and Hill,  1996) measured metabolic rate for six hours after consumption of moderate to large meals and revealed that 57% of the TEF has been expended at three hours, 77% at four hours and 91% at five hours
      • Measurement of RMR, during continuous intravenous or EN that have continued for more than 24 hours, will not be appreciably impacted by TEF, as reported by one neutral-quality non-randomized trial (Heymsfeld et al,  1987)
      • The clinical judgement of registered dietitians who have experience with critical care patients was used to modify the five-hour fast recommendation by adding two clinical situations where long fasts might carry clinical risk.

    • Recommendation Strength Rationale

      • While most studies used three-hour time measures, the ones which measured for six hours were of positive quality and supported a five-hour fast
      • Six studies agree in their conclusions in R.10.1, recommending a five-hour fast
        • Conclusion statement is Grade II
      • The recommendation, R.10.2, that continuous feedings in critical care patients that have been stable for 24 hours, was based on a single study
        • Conclusion statement is Grade III.