Non-invasive ventilation: Effect of a vented and a non-vented CO2 exhalation system on O2- and CO2-concentrations

Abstract

Background Non-ICU ventilators for non-invasive ventilation (NIV) do not produce a fixed FiO2 - supplemental O2 using a constant flow rate has to be added.Moreover, the effects of a non-vented CO2 exhalation system with a controlled valve versus a vented system with a leak port are poorly investigated. Aims and objectives To compare both systems. Methods 10 healthy participants and 10 chronic hypercapnic patients were prospectively ventilated with both systems in an experimental setting. 3 inspiratory/expiratory pressure levels (12/4, 16/4, 20/4 cmH2O) und 3 O2 flow rates (0, 2, 5 l/min.) were systematically varied. To measure O2- and CO2-concentrations in nose and mouth, full-face masks were prepared with small tubes. Furthermore, transcutaneous capnometry was applied. Results An enhancement of the O2 flow rate (0 versus 5 l/min.) increased the O2-concentrations in healthy participants at 7.9±2.1 (vented) vs. 13.6±2.8% (non-vented), and in patients at 7.0±1.6 (vented) vs. 11.7±3.4% (non-vented). At a flow rate of 5 l/min., the differences in O2-concentrations - vented versus non-vented - were both significant (p Conclusion O2-concentrations achieved with a vented system are lower, but CO2 wash-out is higher compared to a non-vented system. These results should be taken into account when selecting an appropriateCO2 exhalation system.