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Flow-Through Versus Sidestream Capnometry for Detection of End Tidal Carbon Dioxide in the Sedated Patient

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Abstract

Background

End tidal carbon dioxide (ETCO2) 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 ETCO2 than sidestream capnometry when evaluated in a bench study during low tidal volumes and high oxygen administration via nasal cannula. Secondarily, when ETCO2 from each is compared to arterial CO2 (PaCO2) during a study in which healthy, non-intubated volunteers are tested under normocapnic, hypocapnic and hypercapnic conditions, the flow-through capnometer will resemble PaCO2 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 ETCO2 accuracy using waveforms generated via mechanical lungs during low tidal volumes and high oxygen flow rates. A volunteer study compared the ETCO2 for each capnometer against PaCO2 during sedation in which 8 l O2 was delivered via mask rather than the nasal cannula.

Results

In the bench study, the flow-through capnometer gave slightly higher values of ETCO2 during high-flow oxygen and no discernable differences during variable tidal volumes. Bland and Altman plots comparing ETCO2 to PaCO2 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.

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Acknowledgments

Funding. This work was supported by financial contributions from Nihon Kohden Corporation, Japan. Potential Conflict of Interest. Authors Isao Matsubara and Shinji Yamamori have a potential conflict of interest. Isao Matsubara and Shinji Yamamori receive salary from Nihon Kohden Corporation, Japan, the company that funded the research.

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Correspondence to Derek J. Sakata MD.

Additional information

Sakata DJ, Matsubara I, Gopalakrishnan NA, Westenskow DR, White JL, Yamamori S, Egan TD, Pace NL. Flow-through versus sidestream capnometry for detection of end tidal carbon dioxide in the sedated patient.

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Sakata, D.J., Matsubara, I., Gopalakrishnan, N.A. et al. Flow-Through Versus Sidestream Capnometry for Detection of End Tidal Carbon Dioxide in the Sedated Patient. J Clin Monit Comput 23, 115–122 (2009). https://doi.org/10.1007/s10877-009-9171-2

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  • DOI: https://doi.org/10.1007/s10877-009-9171-2

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