Determination of metabolic monitor errors and precision under clinical conditions

Abstract

Background & Aims: Metabolic monitoring devices used in the critical care setting are subject to a range of conditions that may compromise their accuracy. We sought to investigate the error and precision of the Deltatrac metabolic monitor under these conditions. Methods: A modified version of the funnel burner, described by Miodownik et al. (8), was ventilated by a mechanical ventilator. This was used to examine the performance of the Deltatrac metabolic monitor over a wide range of inspired oxygen concentrations, minute ventilation, and positive end expiratory pressure at different levels of oxygen consumption and carbon dioxide production. Results: The Deltatrac measured VO2 with a mean error ± precision of 9.4% ± 19.5% (range, 9.3% ± 1.9%-72.6% ± 13.6%). The mean VCO2 error ± precision was 1.2% ± 3.1% (range-2.0% ± 1.2%-5.4% ± 3.1%). Error was significantly affected by oxygen concentration and minute ventilation but was largely independent of positive and expiratory pressure. Conclusions: The methodology of Miodownik et al. permits the expression of metabolic device errors over a wide range of simulated clinical conditions. © 2001 Harcourt Publishers Ltd.