- Accuracy of EE measurements in ICU patients on non-invasive mechanical ventilation Design: Prospective, controlled, observational multicenter study. Subjects: 182 ICU patients. Sample size calculation is based on the estimated accuracy of the new IC device compared to the Deltatrac, when performed simultaneously on one subject. In a previous study, we found a difference of EE between the Deltatrac and the Quark RMR of 24±220 kcal, thus a coefficient of variation (SD/mean) of 8.8 %. We hypothesized a difference of 25±50 kcal when comparing the Deltatrac with the new IC device, thus a coefficient of variation of 2%. This reduction of 6.5% of the coefficient variation, with a power of 90% and a significance level of 0.05 was used to calculate a required sample size of 91 subjects. A drop out rate of 50% is anticipated, leading to 182 patients to be recruited to allow an analysis based on 91 patients with optimal measurements.