Indirect calorimetry in patients with active respiratory infection — prevention of cross-infection

Background: Measurement of resting energy expenditure in patients with active respiratory infection is hampered by the risk of contamination of indirect calorimeters and connecting tubes that cannot be sterilized. This validation study tested whether the use of disposable standard-bore air tubes and an antibacterial filter, by reducing air flow, introduces an error due to recirculation of expired air in the canopy. Methods: Eleven healthy volunteers underwent indirect calorimetry twice in random order, using a Deltatrac calorimeter either with standard wide-bore tubing or with a disposable standard-bore air tube and filter. Methods were compared by Bland–Altman plots and by calculating trends over time. Results: The new tube and filter reduced air flow by 40%. Measured resting energy expenditure did not differ significantly between methods, with limits of agreement −135 to +188 kcal/d. Carbon dioxide flow (VCO2) and respiratory quotient (RQ), but not oxygen flow decreased slowly over time with both methods. Conclusions: The use of an air filter and standard-bore tubes do not introduce a systematic error into indirect calorimetry. Although trends in VCO2 and RQ are consistent with minor recirculation of exhaled air, this modified Deltatrac™ system can be safely and reliably used to measure resting energy expenditures in patients with active tuberculosis and other airborne infection.