Can positive airway pressure therapy still leave residual respiratory events or nocturnal hypoxemia?

PAP is highly effective when appropriately titrated and delivered, but it does not by itself guarantee normalization of respiratory events or overnight oxygenation. In an 83-year-old patient, persistent abnormalities warrant determining whether the issue is residual upper-airway obstruction, impaired device delivery, or nonobstructive gas-exchange failure.

Clinical evidence

• Effective PAP titration requires a low residual respiratory disturbance index/AHI, adequate oxygenation, and acceptable unintentional leak, ideally verified during supine REM sleep. Inadequate pressure and mask leak are established, modifiable reasons treatment may remain ineffective.
• Residual events are not rare: device-derived residual AHI was >5 events/hour in approximately 32.3% of users, although automated device algorithms may miss some events.
• REM sleep and supine posture are recognized periods of increased vulnerability. Residual REM-supine AHI has been reported during CPAP, supporting review of event timing and body-position patterns rather than relying only on a nightly average AHI.

Hypoxemia, hypoventilation, and cardiopulmonary physiology

• Persistent desaturation may occur despite satisfactory control of obstructive events. In severe obesity hypoventilation syndrome, 43% of patients spent >20% of sleep with SpO₂ below 90% despite obstruction control.
• This pattern is consistent with residual hypoventilation and hypercapnia rather than inadequate airway splinting alone. When hypoxemia or hypercapnia persists without ongoing obstructive events, bilevel noninvasive ventilation may be more appropriate than simply increasing CPAP pressure or adding oxygen.
• Significant cardiopulmonary disease, COPD, heart failure, and suspected sleep-related hypoventilation require individualized assessment, often with attended polysomnography.

Clinical implications

• Review should include pressure adequacy, leak, residual-event morphology and timing, oxygenation, and evidence of hypoventilation before changing treatment modality.

Bottom line

• Residual respiratory events and nocturnal hypoxemia during PAP are evidence-supported consequences of incompletely controlled pressure, leak, REM/positional obstruction, hypoventilation, or cardiopulmonary disease; management should target the identified mechanism rather than assume PAP failure or escalate pressure indiscriminately.