Determination of metabolic monitor errors and precision under clinical conditions

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 V 0 2 with a mean error±precision of 9.4%±19.5% (range, 9.3%±1.9%–72.6%±13.6%). The mean V CO 2 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.