Determining energy expenditure during critical illness: a comparison of three instruments for indirect calorimetry in mechanically ventilated patients.

All study instruments will be connected in parallel, a mandatory 10 minute period is then provided before commencement of gas exchange measurements to allow the Deltatrac mixing chamber to equilibrate with expired gas from the patient after the initial break in the ventilator circuit during connection. Simultaneous measurements with Deltatrac II and either Quark RMR or E-sCOVX will then be performed in a randomized order. After measuring with the first device, another parallel measurement will be performed with the second device and Deltatrac II. Average values for energy expenditure (EE), VO2, VCO2, minute ventilation (MV) and respiratory quotient (RQ) will be registered after a 20 minute period. Measurements where the reference method registers a mean RQ of <0.6 or >1.2 will be discarded. All aspects of the patient's ICU therapy are determined by the attending physician. Changes in ventilator settings, disconnection of the ventilator circuit or patient mobilization are to be avoided during and one hour previous to measurements unless deemed necessary by medical staff. In such event the ongoing measurement will be discontinued and restarted after a 15 minute resting period.