Quick Links

Recommendations Summary

CI: Gas Collection Devices 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: Gas Collection Devices and Air Leaks

    Use rigorous adherence to manufacturers' equipment guidelines to prevent air leaks. Air leaks will result in RMR measurement errors.

    Rating: Weak

    CI: Gas Collection Devices and Accuracy

    Further studies comparing modern gas collection devices (including rigid canopies, facemasks, tubing connections, sampling lines and mouthpieces with nose clips) are needed in clinical populations. Inaccurate gas collection will result in an inaccurate measurement.

    Rating: Insufficient Evidence

    • Risks/Harms of Implementing This Recommendation

      Some patients may experience anxiety or claustrophobia with some gas collection devices, resulting in artificially high RMR measures. In this case, a different device should be used or the patient should not be measured. 

    • Conditions of Application

      In patients breathing room air,  gas collection device selection may need to be individualized for patients with certain facial characteristics (i.e.,  very thin, obese,  head and neck surgery, full beards).

    • Potential Costs Associated with Application

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

    • Recommendation Narrative

      • Several types of gas collection devices are available for indirect calorimetry
      • In indirect calorimetry studies, in which the devices were carefully monitored to ensure that no air leaks were occurring, one time series study of positive quality (Isbell et al,  1991),  two reliability studies of neutral quality (Askanazi et al,  1980; McAnena et al,  1986) and one non-randomized trial with concurrent controls study of negative quality (Schols et al,  1992), suggested that RMR measures are comparable among these devices
      • In one neutral quality reliability study (Forse,  1993), however, mean RMR was 7% higher for face mask and 9% higher for mouthpiece than for canopy measurements
      • Recent design improvements in face masks and mouthpieces have not been tested, so further studies are needed to determine whether these devices give RMR values equivalent to those measured with rigid canopy systems
      • There seems little difference in RMR measurement results, based on type of gas collection device used, provided the devices are used carefully (Compher et al, 2006)
        • With all devices, air leaks will result in artificially low RMR values
          • With the facemask, it is important to ensure that the mask fits tightly on the subject’s face and a sealant may be needed to avoid air leaks
          • With the mouthpiece and nose clip, the best size mouthpiece should be selected for each subject and the operator should ensure that the subject cannot breathe in or out through the nose after the clip is in position and that there is a good lip seal around the mouthpiece
          • For the canopy, air leaks can occur if the plastic sheet is not completely tucked in or if the plastic sheet around the canopy is not tight-fitting.
        • For any patient who expresses a feeling of claustrophobia with the facemask or canopy in place, the mouthpiece and nose clip would be a better choice
        • For those who feel uncomfortable with the nose clip, either the facemask or canopy could be offered.

    • Recommendation Strength Rationale

      • A series of four studies, quality ranging from positive to negative, agreed that the proper use of the gas collection device had limited impact on RMR measures, while a single neutral quality study showed less than a 10% difference
      • Based on slight disagreement on using rigorous adherence to prevent air leaks in R.9.1, the conclusion statement is Grade III
      • Since no published studies were found comparing most of the gas collection devices in use today, the statement regarding needed research in R.9.2 is based on the opinion of the expert panel.