Contribution of Average Volume Assured Pressure Support (AVAPS) to Efficacy of bi-Level Pressure Support Nocturnal Ventilation and Impact on Sleep Structure

This study aims to compare, in a randomized order, two consecutive nights with a bi-level positive pressure ventilator (Synchrony, Respironics, USA), with and without average volume assured pressure support (AVAPS), in patients with chronic respiratory failure, treated on a long term basis by home nocturnal non-invasive ventilation.

Specific endpoints are :

• quality of sleep assessed by polysomnography scored by an independent investigator (sleep efficiency, distribution of sleep stages, arousals and sleep stage changes) and subjective scores (St Mary's questionnaire),
• perception of comfort of ventilation (clinical score),
• efficacy of ventilation (pulsoximetry, transcutaneous capnography (Tina TCM4 Radiometer, Copenhagen), effective ventilation and tidal volumes, leaks as measured by ventilator, Stardust software, Respironics).

Patients: Fourteen patients with obesity-hypoventilation and/or COPD, treated and stable for at least 3 months, will be included and undergo complete sleep studies in Geneva University Hospital's Sleep Laboratory. Patients included must be compliant to treatment (at least 4 hours of use of ventilator/night).

Methods: Patients are blinded as to whether or not AVAPS is implemented. Target tidal volume is set at 7-8 ml/kg. EPAP (Expiratory positive airway pressure) level is unchanged. Minimal IPAP (Inspiratory positive airway pressure) level is set at usual IPAP - 3 cm H2O. Maximal IPAP is set between 25 and 30 cm H2O. Back up frequency is unchanged.