Lung Morphology

Formalin-fixed and paraffin-embedded lung sections (4 μm) were stained with hematoxylin and eosin to assess lung morphology. Lung morphology was quantified based on a previously described lung injury score with inclusion of alveolar septal thickening.¹³ Per lung section, 10 snapshots were scored in a blinded manner on 400× magnification for 5 independent variables: (1) inflammatory cell influx in interstitium and alveolar space; (2) thickening of the alveolar septa; (3) intraalveolar and extraalveolar hemorrhage; (4) intraalveolar edema; and (5) overinflation. The variables were scored from 0 to 4: 0 = negative, 1 = slight, 2 = moderate, 3 = high, and 4 = severe. Total lung morphology scores were calculated by the sum of the scored variables.