Respiratory Pattern and Tidal Volumes Differ for Pressure Support and Volume-assured Pressure Support in Amyotrophic Lateral Sclerosis

Rationale: Amyotrophic lateral sclerosis (ALS) is a progressive neuromuscular disease resulting in respiratory failure and death. Use of noninvasive ventilation (NIV) improves survival. However, use of volume-assured pressure support (VAPS) has not been extensively studied in ALS. Objectives: To explore the clinical usefulness of a detailed evaluation of device-recorded NIV data in the management of chronic respiratory failure in ALS, and to determine whether there are differences in efficacy between patients using VAPS or PS. Methods: We performed a retrospective chart review of 271 patients with ALS using either PS or VAPS, along with an evaluation of device-recorded data to explore differences in attainment of goal tidal volumes (VT) and ratio of respiratory rate to tidal volume (f/VT), in addition to triggering and cycling ability. Results: Two hundred and fifteen patients were using PS, while 56 were using VAPS. There were no significant differences in demographic data, symptoms, pulmonary function, or patient compliance. Compared with VAPS, achieved VT was significantly lower for PS while f/VT was significantly higher. Percent spontaneous triggering was relatively preserved in both cohorts, whereas percent spontaneous cycling was considerably decreased in both. Furthermore, there was no association found between spontaneous triggering or cycling, and pulmonary function, indicating the presence of low spontaneous breath cycling or triggering ability is difficult to predict. Conclusions: Examination of device data for exhaled tidal volumes and f/VT may be of use in evaluating efficacy of NIV in ALS. VAPS provides more reliable goal VT than does PS, and is associated with decreased f/VT. Spontaneous cycling is decreased in ALS despite preservation of triggering ability. Although a set backup rate may address decreased triggering, perhaps more importantly, setting a sufficient fixed inspiratory time would address the issue of decreased cycling.