End-tidal carbon dioxide concentration monitoring in obstructive sleep apnea patients
The objective of this study was to investigate the end-tidal carbon dioxide concentration (ETco(2)) monitoring in obstructive sleep apnea (OSA) patients during sleep and to explore whether the ETco(2) value may explain a significant portion of the relationship between ETco(2) value and apnea/hypopnea index (AHI) and nocturnal oxygenation indices. Thirty-eight consecutive patients underwent overnight polysomnography and were synchronously monitored for ETco(2) using an microstream capnometer. Mean and maximum values during wake time and different sleep stages were recorded. We grouped 38 OSA patients into 2 subgroups on the basis of their difference of mean total sleep time and wake time ETco(2) [(T - W) ETco(2)]; one group, 20 patients with (T - W) ETco(2) less than 0, and the other group,18 patients with (T - W) ETco(2) greater than 0. Group with (T - W) ETco(2) less than 0 patients exhibited higher AHI (mean ± SD, 68.58 ± 22.78 vs. 27.61 ± 19.44 events/h) and lower nocturnal oxygenation indices (minimum Sao(2), 67.85 ± 10.08 vs. 82.61% ± 6.07%; mean Sao(2), 91.29 ± 3.31 vs. 95.15% ± 1.88%) compared with the other group. In summary, the study provides preliminary data showing that ETco(2) potentially can be used in continuous monitoring of OSA patients. And, (T - W) ETco(2) can indicate the severity of OSA.