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

Abstract

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 (ΔP 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 ΔP S level. In the first block, the effects of three levels of variability were tested at constant ΔP S: 0% (PSV0%, conventional PSV), 15% (vPSV15%), and 30% (vPSV30%). In the second block, two levels of variability (0% and variability set to achieve ±5 cmH2O variability) were tested at two ΔPS levels (baseline ΔP S and ΔP S reduced by 5 cmH2O from baseline). The following four ventilation strategies were tested in the second block: PSV with baseline ΔP S and 0% variability (PSVBL) or ±5 cmH2O variability (vPSVBL), PSV with ΔPS reduced by 5 cmH2O and 0% variability (PSV-5) or ±5 cmH2O 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 vPSV15% and vPSV30% compared with PSV0%. The variability of tidal volume (V T) was higher with vPSV15% and vPSV30% compared with PSV0%. The incidence of asynchronies and the variability of transpulmonary pressure (P L) were higher with vPSV30% compared with PSV0%. 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 vPSVBL compared with PSVBL. 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.

Keywords: acute respiratory distress (ARDS); assisted ventilation; asynchronies; respiratory mechanic; variable pressure support ventilation.

Conflict of interest statement

MG was granted a patent on the variable pressure support ventilation mode of assisted ventilation (noisy PSV), which has been licensed to Dräger Medical AG (Lübeck, Germany). The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Copyright © 2021 Ball, Sutherasan, Fiorito, Dall'Orto, Maiello, Vargas, Robba, Brunetti, D'Antini, Raimondo, Huhle, Schultz, Rocco, Gama de Abreu and Pelosi.

Figures

Figure 1

Time course of interventions. Within each intervention block, different ventilation settings were delivered in random order. PSV0%, conventional PSV ventilation with no variability; vPSV15%, variable PSV with variability set to 15% CV; vPSV30%, variable PSV with variability set to 30% CV; PSVBL, PSV with no variability and baseline ΔPS as per clinical indication; vPSVBL, variable pressure support with variability set to achieve ±5 cmH2O and baseline ΔPS as per clinical indication; PSV−5, PSV with no variability and ΔPS reduced by 5 cmH2O from the baseline value; vPSV−5, variable PSV with variability set to achieve ±5 cmH2O and ΔPS reduced by 5 cmH2O from the baseline value; PSV, pressure support ventilation; CV, coefficient of variation.

Figure 2

Representative respiratory traces of a patient during conventional (left) and variable (right) pressure support ventilation. Pao, pressure at the airway opening; Pes, esophageal pressure.

Figure 3

Respiratory mechanics at different levels of variability (block 1). Variables are reported as the difference from the median value achieved during PSV0% to allow between-patients visual comparisons. Dashed lines represent the medians of each ventilation step. PSV0%, conventional PSV ventilation with no variability; vPSV15%, variable PSV with variability set to 15% CV; vPSV30%, variable PSV with variability set to 30% CV; CV, coefficient of variation; ΔPS, pressure support; ΔPes, esophageal pressure swings; PL, peak transpulmonary pressure.

Figure 4

Effects of variability on the distribution of respiratory mechanics parameters at different levels of pressure support (block 2). Variables are reported as the difference from the median value achieved during PSVBL to allow between-patients visual comparisons. Dashed lines represent the medians of each ventilation step. PSVBL, PSV with no variability and baseline ΔPS as per clinical indication; vPSVBL, variable pressure support with variability set to achieve ±5 cmH2O and baseline ΔPS as per clinical indication; PSV−5, PSV with no variability and ΔPS reduced by 5 cmH2O from the baseline value; vPSV−5, variable PSV with variability set to achieve ±5 cmH2O and ΔPS reduced by 5 cmH2O from the baseline value; PSV, pressure support ventilation; CV, coefficient of variation; ΔPS, pressure support; ΔPes, esophageal pressure swings; PL, peak transpulmonary pressure.

Figure 5

Associations between respiratory mechanics parameters and the pressure level received in the preceding breath during variable PSV. Squares and confidence intervals refer to the effect estimate for ΔPS in a mixed model comprising the ΔPS received during the preceding breath as a fixed effect and the patient as a random effect with random intercept. The units of the estimates are expressed in the untransformed units of the variables, i.e., they represent the absolute change in VT, ΔPes, or PL when the ΔPS received during the preceding breath increases by 1 cmH2O. vPSVBL, variable PSV with variability set to achieve ±5 cmH2O and baseline ΔPS as per clinical indication; vPSV−5, variable PSV ventilation with variability set to achieve ±5 cmH2O and ΔPS reduced by 5 cmH2O from the baseline value; PBW, predicted body weight; PSV, pressure support ventilation; ΔPS, pressure support; VT, tidal volume; ΔPes, esophageal pressure swings; PL, peak transpulmonary pressure. *Significant association (p < 0.05).