[Energy expenditure at rest: indirect calorimetry vs the Fick principle]

The objectives of this study ere to assess the reproducibility of the energy expenditure at rest in patients with mechanical ventilation, using the indirect calorimetry method and the Fick principle, and to verify whether both methods of measuring the energy expenditure, are interchangeable. 15 critically ill patients on mechanical ventilation were studied. Each study consisted of the determination, in duplicate, of the energy expenditure at rest, using indirect calorimetry and the Fick principle. Each patient was studied on two occasions, thus yielding a total of 30 studies. The determination of the energy expenditure at rest using indirect calorimetry was carried out using an apparatus based on the closed circuit method (Calorimet), and the Fick principle was carried out using a thermodilution catheter placed in the pulmonary artery. The reproducibility coefficient of the indirect calorimetry method was 132 kcal/day, which is equivalent to 7% of the average energy expenditure at rest. The reproducibility coefficient of the Fick method was 344 kcal/day, which is equivalent to 18% of the average energy expenditure at rest. The difference between both methods, 6 +/- 50 kcal/day, was not significant. The corresponding limits in both methods were between-306 kcal/day and 294 kcal/day, which is equivalent to 15% of the average energy expenditure at rest.

The determination of the energy expenditure at rest using the Fick method, has a worse reproducibility coefficient that obtained by indirect calorimetry, but from a clinical point of view, both methods are interchangeable.