Thorax doi:10.1136/thoraxjnl-2011-201081
  • Sleep disordered breathing
  • Original article

Volume targeted versus pressure support non-invasive ventilation in patients with super obesity and chronic respiratory failure: a randomised controlled trial

  1. Nicholas Hart4
  1. 1Division of Asthma, Allergy and Lung Biology, Department of Asthma, Allergy and Respiratory Science, King's College London, London, UK
  2. 2Lane Fox Translational Respiratory Research Unit, Guy's and St Thomas' NHS Foundation Trust, London, UK
  3. 3National Institute for Health Research Respiratory Biomedical Research Unit, Royal Brompton and Harefield NHS Foundation Trust and Imperial College, London, UK
  4. 4Guy's and St Thomas' NHS Foundation Trust and King's College London, National Institute of Health Research Comprehensive Biomedical Research Centre, London, UK
  1. Correspondence to Dr Patrick B Murphy, Lane Fox Respiratory Unit, St Thomas' Hospital, Westminster Bridge Road, London SE1 7EH, UK; patrick.b.murphy{at}
  1. Contributors Conception and design: NH, MIP, JM; data collection: PM; analysis and data interpretation: PM, NH, MIP, JM; manuscript drafting: PM, ACD, AS, MH, NSH, AJW, JM, MIP, NH.

  • Received 8 September 2011
  • Accepted 26 January 2012
  • Published Online First 1 March 2012


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


  • Descriptor number 4.13: Ventilation: Non-Invasive/Long-Term/Weaning.

  • Funding The study was supported by an unrestricted educational grant from Philips-Respironics. The funder was not involved in study design, data collection or analysis, decision to publish or preparation of this manuscript. Philips-Respironics provided the BiPAP Synchrony and Actiwatch 64 devices used in the study. The authors acknowledge financial support from the Department of Health via the National Institute for Health Research (NIHR) comprehensive Biomedical Research Centre award to Guy's and St Thomas' NHS Foundation Trust in partnership with King's College London and King's College Hospital NHS Foundation Trust and the NIHR Respiratory Disease Biomedical Research Unit at the Royal Brompton and Harefield NHS Foundation Trust and Imperial College, London.

  • Competing interests The Lane Fox Translational Respiratory Research Group has received unrestricted research grants from ResMed, Abingdon, Oxfordshire, UK; Philips-Respironics, Murrysville, Pennsylvania, USA; Fisher & Paykel Healthcare, Auckland, New Zealand; and B & D ElectroMedical, Stratford-upon-Avon, Warwickshire, UK. PM has received expenses for travel to conferences from Philips-Respironics. AJW has received expenses for travel to conferences from ResMed. NH has received fees for lecturing from Philips-Respironics and Fisher & Paykel. MIP has received fees for lecturing from Philips-Respironics. This study was supported by Philips-Respironics, Murrysville, Pennsylvania, USA. The study design, results, interpretation of the findings or any other subject discussed in the submitted manuscript were not dependent on support.

  • Ethics approval Guy's REC.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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