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Background:  Variable pressure support ventilation (vPSV) is an assisted ventilation mode that varies the level of pressure support on a breath-by-breath basis to restore the physiological variability of breathing activity. We aimed to compare the effects of vPSV at different levels of variability and pressure support (Δ P  S ) in patients with acute respiratory distress syndrome (ARDS).   Methods:  This study was a crossover randomized clinical trial. We included patients with mild to moderate ARDS already ventilated in conventional pressure support ventilation (PSV). The study consisted of two blocks of interventions, and variability during vPSV was set as the coefficient of variation of the Δ P  S  level. In the first block, the effects of three levels of variability were tested at constant Δ P  S : 0% (PSV 0% , conventional PSV), 15% (vPSV 15% ), and 30% (vPSV 30% ). In the second block, two levels of variability (0% and variability set to achieve ±5 cmH 2 O variability) were tested at two ΔP S  levels (baseline Δ P  S  and Δ P  S  reduced by 5 cmH 2 O from baseline). The following four ventilation strategies were tested in the second block: PSV with baseline Δ P  S  and 0% variability (PSV BL ) or ±5 cmH 2 O variability (vPSV BL ), PSV with ΔP S  reduced by 5 cmH 2 O and 0% variability (PSV −5 ) or ±5 cmH 2 O variability (vPSV −5 ). Outcomes included gas exchange, respiratory mechanics, and patient-ventilator asynchronies.   Results:  The study enrolled 20 patients. In the first block of interventions, oxygenation and respiratory mechanics parameters did not differ between vPSV 15%  and vPSV 30%  compared with PSV 0% . The variability of tidal volume ( V  T ) was higher with vPSV 15%  and vPSV 30%  compared with PSV 0% . The incidence of asynchronies and the variability of transpulmonary pressure ( P  L ) were higher with vPSV 30%  compared with PSV 0% . In the second block of interventions, different levels of pressure support with and without variability did not change oxygenation. The variability of  V  T  and  P  L  was higher with vPSV −5  compared with PSV −5 , but not with vPSV BL  compared with PSV BL .   Conclusion:  In patients with mild-moderate ARDS, the addition of variability did not improve oxygenation at different pressure support levels. Moreover, high variability levels were associated with worse patient-ventilator synchrony.   Clinical Trial Registration:   www.clinicaltrials.gov , identifier: NCT01683669.

frontiers in physiology

Effects of Different Levels of Variability and Pressure Support Ventilation on Lung Function in Patients With Mild–Moderate Acute Respiratory Distress Syndrome