Abstract

BackgroundPendelluft and expiratory muscle activity during spontaneous breathing should be minimized to reduce potential harmful effects. This study aimed to describe pendelluft and expiratory muscle activity in hypoxemic patients recovering spontaneous breathing after >= 72 h of lung-protective, fully controlled mechanical ventilation (MV) and assess the effect of pressure support ventilation (PSV) and positive end-expiratory pressure (PEEP). MethodsA physiological, randomized crossover study was conducted in hypoxemic patients receiving three levels of PSV: 5, 10, and 15 cmH(2)O, and two PEEP levels: based on electrical impedance tomography before spontaneous breathing (PEEPEIT) or according to PEEP-FiO(2) tables (PEEPARDS). Pendelluft was defined as the percentage of volume displaced from non-dependent to dependent lung regions during inspiration. Expiratory muscle activity was assessed by the expiratory rise in gastric pressure (Delta Pga(EXP)), and inspiratory effort was estimated using muscular pressure (Pmus). Statistical analyses included linear mixed-effects models and mediation analyses. ResultsFifteen patients were enrolled (mean PaO2/FiO(2 )ratio: 262 +/- 51 mmHg; median duration of MV: 9 [5-13] days; 6 females). PEEPEIT was 11 [10-13] cmH(2)O and PEEPARDS 6 [5-7] cmH(2)O. Expiratory muscle activity was observed in 13 patients. Compared to PS 5 cmH(2)O, PS to 10 and 15 cmH(2)O, adjusted for PEEP, significantly reduced both pendelluft and Delta Pga(EXP) (p < 0.001). When adjusted for PS, PEEPEIT was associated with a slight reduction in pendelluft (p = 0.039) but a concomitant increase in Delta Pga(ET) (p = 0.007) compared to PEEPARDS. The mediation analysis revealed a significant negative mediating effect of Delta Pga(EXP) on the relationship between PEEPEIT and pendelluft (p < 0.001). Pmus, which was also significantly associated with pendelluft magnitude (p < 0.001), mediated the effect of PS on reducing pendelluft (p = 0.048), but not that of PEEP (p = 0.46). ConclusionsIn patients with ARDS transitioning to spontaneous breathing, increasing PS reduces pendelluft and expiratory muscle activity. Higher PEEP can decrease pendelluft, but its effect can be counteracted by increased expiratory activity.