A Novel Mainstream Capnometer System for Non-invasive Positive Pressure Ventilation.

Capnometry is a method to measure carbon dioxide (CO2) in exhaled gas and it has been used to monitor patient respiratory status. CO2 monitoring is also used for patients receiving non-invasive positive pressure ventilation (NPPV) therapy during mechanical ventilation. Ventilators actively dilute exhaled gas during non-invasive ventilation. In order to accurately measure end-tidal CO2, an adequate amount of expired gas needs to be filled in a CO2 measurement cell before expiratory positive airway pressure (EPAP) gas from the ventilator arrives to the cell. This is the reason why it is difficult to measure CO2 stably during non-invasive ventilation using the conventional CO2 measurement method. Therefore, we developed NPPV cap-ONE mask, which accurately measures CO2 in exhaled gas during non-invasive ventilation. In this study, we evaluated the basic performance of the NPPV cap-ONE mask system. The NPPV cap-ONE mask system could accurately measure CO2 in exhaled gas comparing to the conventional device in this study.

Flow-through versus sidestream capnometry for detection of end tidal carbon dioxide in the sedated patient.

BACKGROUND: End tidal carbon dioxide (ETCO(2)) in non-intubated patients can be monitored using either sidestream or flow-through capnometry [Yamamori et al., J Clin Monit Comput 22(3):209-220, 2008]. The hypothesis of this validation study is that, flow-through capnometry will yield a more accurate estimate of ETCO(2) than sidestream capnometry when evaluated in a bench study during low tidal volumes and high oxygen administration via nasal cannula. Secondarily, when ETCO(2) from each is compared to arterial CO(2) (PaCO(2)) during a study in which healthy, non-intubated volunteers are tested under normocapnic, hypocapnic and hypercapnic conditions, the flow-through capnometer will resemble PaCO(2) more closely than the sidestream capnometer. This will be especially true during periods of lower minute ventilation and high oxygen flow rates via mask in non-intubated, remifentanil sedated, healthy volunteers whose physiologic deadspace is small. METHODS: The performance of a flow-through (cap-ONE, Nihon Kohden, Tokyo, Japan) and a sidestream (Microcap Smart CapnoLine Plus, Oridion Inc., Needham, MA) capnometer were compared in a bench study and a volunteer trial. A bench study evaluated ETCO(2) accuracy using waveforms generated via mechanical lungs during low tidal volumes and high oxygen flow rates. A volunteer study compared the ETCO(2) for each capnometer against PaCO(2) during sedation in which 8 l O(2) was delivered via mask rather than the nasal cannula. RESULTS: In the bench study, the flow-through capnometer gave slightly higher values of ETCO(2) during high-flow oxygen and no discernable differences during variable tidal volumes. Bland and Altman plots comparing ETCO(2) to PaCO(2) showed essentially equal performance between the two capnometers in the volunteers. CONCLUSIONS: Within a wide limit of agreement between the volunteer and bench study, flow-through and sidestream capnometry performed equally well during bench testing and in non-intubated, sedated patients.