Noninvasive monitoring of CO2 during polysomnography: a review of the recent literature.

Abstract

Sleep-related breathing disorders are complex conditions that require the integration of clinical and sleep laboratory findings to support a diagnosis. Analysis of carbon dioxide (CO2) levels during sleep provides important additional information to the clinician that is not obtained from other polysomnographic indices, and that may have a direct impact on both diagnosis and patient mortality. Although arterial blood gas (ABG) is considered the gold standard for assessing PaCO2 levels, there are numerous drawbacks. Noninvasive methods for PaCO2 estimation include end-tidal and transcutaneous monitoring, which allow for continuous monitoring of trends. Review of the recent literature suggests that transcutaneous methods correlate strongly with PaCO2 levels and can provide an accurate surrogate in replacement of ABGs. End-tidal methods provide breath to breath information that can be used to assess hypoventilation; however, they have more variability, especially in patients with increased dead space and small tidal volumes. To date, however, there are limited studies investigating noninvasive CO2 monitoring during sleep. Given the benefits of CO2 monitoring and the importance of assessing for hypercapnia, noninvasive continuous CO2 monitoring should be considered for all patients undergoing polysomnography.