Background: In acute hypoxemic respiratory failure (AHRF), spontaneous breathing effort can generate excessive regional lung stress and strain manifesting as pendelluft. Higher PEEP may reduce pendelluft and reduce regional lung stress and strain during spontaneous breathing. This study aimed to establish whether higher or lower PEEP ameliorates pendelluft and to characterize factors determining the presence and magnitude of pendelluft during spontaneous breathing efforts. Methods: This study was a randomized crossover trial of higher versus lower PEEP applied after systematically initiating spontaneous breathing in subjects with moderate or severe AHRF. The presence and volume of pendelluft were assessed by electrical impedance tomography (EIT). Results: EIT recordings were available for 20 of 30 subjects enrolled in the trial. After initiating spontaneous breathing, 11/20 exhibited pendelluft (proportion 55% [95% CI 32-76]). Following PEEP titration, the prevalence of pendelluft was not different between higher versus lower PEEP levels (50% vs 50%, P = .55). When present, pendelluft volume was generally small (median 28 [interquartile range 8-93] mL) but ranged as high as 364 mL. Pendelluft was associated with higher respiratory effort (esophageal pressure [Pes] swing [ΔPes] median -15 cm H2O vs ΔPes median -8 cm H2O, P = .01), higher pulmonary flow resistance (median 8 cm H2O/L/s vs median 3 cm H2O/L/s, P < .001), and higher dynamic pulmonary elastance (median 5.0 cm H2O/mL/kg predicted body weight vs median 3.2 cm H2O/mL/kg predicted body weight, P = .03). Conclusions: Pendelluft reflecting increased regional lung stress and strain is likely common during spontaneous breathing effort in patients with AHRF but was not systematically affected by applying higher PEEP. The presence and magnitude of pendelluft depended on respiratory effort and lung mechanics.
Keywords: Acute hypoxemic respiratory failure; EIT; Pendelluft; inspiratory effort.