Autotitrating non-invasive ventilation (NIV) in patients with hypercapnic ventilatory failure

Abstract

Non-invasive ventilation (NIV) is an evidenced based treatment of alveolar hypoventilation in patients with hypercapnic respiratory failure (HRF). Volume assured pressure support (VAPS) is a new mode of NIV that aims to maintain alveolar ventilation (VA) by autotitration of the pressure support (PS) delivered to a patient in response to changes in respiratory physiology. The overall aim of this thesis was to investigate the use of VAPS ventilation in patients with chronic HRF during wakefulness and sleep, specifically in the detection and treatment of acute exacerbations. Specific aims were to: a) determine if VA was maintained during VAPS ventilation in patients, with obstructive and restrictive pathologies, specifically during during exacerbations, and sleep (Chapters 3 and 4). b) determine the mechanism(s) of presumed maintenance of VA (Chapters 3 and 4). c) determine whether changes in the ventilator-measured respiratory parameters can be used to identify or predict exacerbations (Chapter 3). d) determine if VAPS can be used clinically to treat ventilatory failure as effectively as standard PS NIV in acute hypercapnic exacerbations of chronic respiratory disease, and in patients naive to NIV therapy (Chapters 5 and 6). I have concluded that VAPS ventilation provides an alternative ventilatory mode to standard PS ventilation, and can effectively maintain VA during sleep, and during exacerbations, when lung characteristics are changing. The mechanism of VA maintenance is likely to be the integration of complex patient-ventilator interactions, with large variability between patients, independent of diagnosis. Further studies of patient-ventilator interaction and its impact on the target ventilation may be aided by measuring respiratory drive or diaphragm work. Changes in ventilator-measured parameters were not predictive of impending exacerbation. Clustering may help to understand the physiological characteristics of exacerbations and individual ventilatory responses, and also to determine whether an autotitrating iVAPS improves outcomes of exacerbations, including survival.