| Abstract
| - Introduction. Automatic titration modes of non-invasive ventilation, including average volume assured pressure support (AVAPS), are hybrid technologies that target a set volume by automated adjustment of pressure support (PS). These automated modes could offer potential advantages over fixed level PS, in particular, in patients who are super obese. Methods. Consecutive patients with obesity hypoventilation syndrome were enrolled in a two-centre prospective single-blind randomised controlled trial of AVAPS versus fixed-level PS using a strict protocolised setup. Measurements. The primary outcome was change in daytime arterial PCO2 (PaCO2) at 3 months. Body composition, physical activity (7-day actigraphy) and health-related quality of life (severe respiratory insufficiency questionnaire, SRI) were secondary outcome measures. Results. 50 patients (body mass index 50±7 kg/m2; 55±11 years; 53% men) were enrolled with a mean PaCO2 of 6.9±0.8 kPa and SRI of 53±17. 46 patients (23 AVAPS and 23 PS) completed the trial. At 3 months, improvements in PaCO2 were observed in both groups (AVAPS ∆0.6 kPa, 95% CI 0.2 to 1.1, p<0.01 vs PS ∆0.6 kPa, 95% CI 0.1 to 1.1, p=0.02) but no between-group difference (∆−0.1 kPa, 95% CI −0.7 to 0.6, p=0.87). SRI also improved in both groups (AVAPS ∆11, 95% CI 6 to 17, p<0.001 vs PS ∆7, 95% CI 1 to 12, p=0.02; between groups ∆5, 95% CI −3 to 12, p=0.21). Secondary analysis of both groups combined showed improvements in daytime physical activity that correlated with reduction in fat mass (r=0.48; p=0.01). Conclusion. The study demonstrated no differences between automated AVAPS mode and fixed-level PS mode using a strict protocolised setup in patients who were super obese. The data suggest that the management of sleep-disordered breathing may enhance daytime activity and promote weight loss in super-obese patients. Trial registration details available at http://www.controlled-trials.com/ISRCTN63940700
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