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Transcutaneous Measurement of Carbon Dioxide Tension During Extended Monitoring: Evaluation of Accuracy and Stability, and an Algorithm for Correcting Calibration Drift

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BACKGROUND: When polysomnography is indicated in a patient with a presumed sleep disorder, continuous monitoring of arterial carbon dioxide tension (PaCO2) is desirable, especially if nocturnal hypoventilation is suspected. Transcutaneous CO2 monitors (PtcCO2) provide a noninvasive correlate of PaCO2, but their accuracy and stability over extended monitoring have been considered inadequate for the diagnosis of hypoventilation. We examined the stability and accuracy of PtcCO2 measurements and the performance of a previously described linear interpolation technique designed to correct for calibration drift. METHODS: We compared the PtcCO2 values from 2 TINA TCM-3 monitors to PaCO2 values from arterial blood samples obtained at the beginning, every 15 min of the first hour, and then hourly over 8 hours of monitoring in 6 hemodynamically stable, male, intensive care patients (mean age 46 ± 17 y). RESULTS: Time had a significant (P = .002) linear effect on the PtcCO2-PaCO2 difference, suggesting calibration drift over the monitoring period. We found no differences between monitor type or interaction between time and monitor type. For the 2 monitors the uncorrected bias was 3.6 mm Hg and the limits of agreement were −5.1 to 12.3 mm Hg. Our linear interpolation algorithm improved the bias and limits of agreement to 0.4 and −5.5 to 6.4 mm Hg, respectively. CONCLUSIONS: Following stabilization and correction for both offset and drift, PtcCO2 tracks PaCO2 with minimal residual bias over 8 hours of monitoring. Should future research confirm these findings, then interpolated PtcCO2 may have an increased role in detecting sleep hypoventilation and assessing the efficacy of treatment.

Keywords: carbon dioxide monitoring; polysomnography

Document Type: Research Article

DOI: http://dx.doi.org/10.4187/respcare.00454

Affiliations: Institute for Breathing and Sleep, Austin Hospital, Heidelberg, Australia

Publication date: April 1, 2011

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