Non-invasive PCO₂ monitoring during polysomnography: transcutaneous versus end-tidal measurement

The objectives of this study were to monitor transcutaneous and end-tidal partial pressures of CO₂ simultaneously during polysomnography, determine the advantages and disadvantages of each method, and identify relevant factors that can affect the results.

This cross-sectional study enrolled 55 adults who underwent polysomnography at the Ajou University Hospital Sleep Center between February 2021 and September 2022. They were volunteers who spontaneously breathed room air. Polysomnography reports, including those of CO₂ monitoring, of all participants were reviewed and analyzed by sleep experts. Generalized Estimation Evaluation, Bon Ferroni Post Hoc and multivariable regression analysis were used for statistical analysis.

Throughout all sleep stages, the mean, highest, and lowest values of end-tidal and transcutaneous partial pressure of CO₂ showed significant differences. The mean transcutaneous partial pressure was higher than the mean end-tidal partial pressure by 2.53 mmHg. The apnea index, apnea-hypopnea index, and height were significant factors affecting the difference between the mean transcutaneous and end-tidal partial pressure of CO₂. As the obstructive sleep apnea grade increased, the mean end-tidal CO₂ partial pressure value decreased. Two patients had hypoventilation; one met the criteria based on the transcutaneous partial pressure of CO₂ and the other met those based on the end-tidal partial pressure of CO₂.

During diagnostic sleep studies, the application of both transcutaneous and end-tidal measurements is suggested for stable and accurate monitoring of partial pressure of CO₂ and complementary analysis.