Hypoxemia during bilevel positive airway pressure treatment in patients with obstructive sleep apnea syndrome and chronic respiratory insufficiency.

In patients with obstructive sleep apnea (OSA) syndrome and chronic respiratory insufficiency one of the options of treatment is bilevel positive airway pressure (BPAP) during sleep. The aim of the study was to find out what are the factors influencing the early results of BPAP treatment in such OSA patients. The study was carried out in 55 adult obese patients (mean body mass index 45 ± 7 kg/m(2)), severe OSA syndrome (mean apnea/hypopnea index 62 ± 19), and chronic respiratory insufficiency (mean PaCO(2) 54 ± 5.7 torr) who underwent polysomnography during BPAP treatment. In 31 patients (56%) the mean SaO(2) during sleep was <88% despite the optimal BPAP and oxygen titration: 83 ± 4% during NREM and 81 ± 7% during REM sleep vs. 91 ± 2% and 90 ± 3%, respectively, in the remaining 24 patients (p < 0.001). The patients with advanced hypoxemia during sleep and BPAP treatment had lower forced vital capacity (2.2 ± 0.9 vs. 2.7 ± 0.8 l, p < 0.05), lower diurnal PaO(2) (49 ± 8 vs. 54 ± 7 torr), higher diurnal PaCO(2) (57 ± 5 vs. 52 ± 5 torr, p < 0.01), and higher PaCO(2) during sleep (75 ± 13 vs. 59.5 ± 7.5 torr). In conclusion, in obese patients with severe OSA syndrome and chronic alveolar hypoventilation there is a risk of sleep hypoxemia during BPAP treatment, despite optimal pressure titration.