Net alveolar fluid clearance is associated with lung morphology phenotypes in acute respiratory distress syndrome

Background The acute respiratory distress syndrome (ARDS) is a heterogeneous syndrome that encompasses multiple phenotypes, e.g. with regards to lung morphology as assessed by computed tomography (CT). Focal or non-focal lung morphology may influence the response to positive end-expiratory pressure (PEEP), recruitment manoeuvres and prone position. Lung morphology has been hypothesized to be associated with alveolar fluid clearance (AFC), thus explaining various responses to such therapeutic interventions; however, this hypothesis has not been specifically studied in humans. Methods We measured net AFC rates in 30 patients with ARDS as a secondary data analysis of a prospective single-centre study. Net AFC rates were compared between patients with focal ARDS and those with non-focal ARDS, as assessed by lung CT-scans. Results Net AFC rates were significantly lower in patients with non-focal ARDS (n = 23; median [interquartile range], 1.5 [0–5.5] %/h) as compared to those with focal ARDS (n = 7; 10.3 [4.5–15] %/h) (P = 0.01). The area under the receiver-operating characteristic curve when net AFC rates were used to differentiate the presence from absence of non-focal ARDS was 0.93 (95% confidence interval, 0.81–1). Tidal volumes and PEEP levels differed between focal and non-focal ARDS patients, but there was no difference in arterial oxygenation or in alveolar-capillary permeability. Conclusions Non-focal lung morphology may be characterized by a functional endotype consistent with marked AFC impairment. Despite study limitations and the need for validating studies in larger cohorts, such novel findings may reinforce our understanding of the association between ARDS phenotypes and therapeutic responses.