Influence of ventilatory settings on pendelluft and expiratory muscle activity in hypoxemic patients resuming spontaneous breathing

Pendelluft 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). A physiological, randomized crossover study was conducted in hypoxemic patients receiving three levels of PSV: 5, 10, and 15 cmH₂O, and two PEEP levels: based on electrical impedance tomography before spontaneous breathing (PEEP EIT ) or according to PEEP-FiO 2 tables (PEEP ARDS ). 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 (ΔPga EXP ), and inspiratory effort was estimated using muscular pressure (Pmus). Statistical analyses included linear mixed-effects models and mediation analyses. Fifteen patients were enrolled (mean PaO 2 /FiO 2 ratio: 262 ± 51 mmHg; median duration of MV: 9 [5–13] days; 6 females). PEEP EIT was 11 [10–13] cmH₂O and PEEP ARDS 6 [5–7] cmH₂O. 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 ΔPga EXP ( p < 0.001). When adjusted for PS, PEEP EIT was associated with a slight reduction in pendelluft ( p = 0.039) but a concomitant increase in ΔPga EXP ( p = 0.007) compared to PEEP ARDS . The mediation analysis revealed a significant negative mediating effect of ΔPga EXP on the relationship between PEEP EIT 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). In 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.