Lung inhomogeneities, inflation and [18F]2-fluoro-2-deoxy-d-glucose uptake rate in acute respiratory distress syndrome

The aim of the study was to determine the size and location of homogeneous inflamed/noninflamed and inhomogeneous inflamed/noninflamed lung compartments and their association with acute respiratory distress syndrome (ARDS) severity. In total, 20 ARDS patients underwent 5 and 45 cmH 2 O computed tomography (CT) scans to measure lung recruitability. [ 18 F]2-fluoro-2-deoxy-d-glucose ([ 18 F]FDG) uptake and lung inhomogeneities were quantified with a positron emission tomography-CT scan at 10 cmH 2 O. We defined four compartments with normal/abnormal [ 18 F]FDG uptake and lung homogeneity. The homogeneous compartment with normal [ 18 F]FDG uptake was primarily composed of well-inflated tissue (80±16%), double-sized in nondependent lung (32±27% versus 16±17%, p 18 F]FDG uptake was similarly distributed between the dependent and nondependent lung. The inhomogeneous compartment with normal [ 18 F]FDG uptake represented 4% of the lung volume. The inhomogeneous compartment with high [ 18 F]FDG uptake was preferentially located in the dependent lung (21±10% versus 12±10%, p 2 =0.53, p The homogeneous lung compartment with normal inflation and [ 18 F]FDG uptake decreases with ARDS severity, while the inhomogeneous poorly/not inflated compartment increases. Most of the lung inhomogeneities are inflamed. A minor fraction of healthy tissue remains in severe ARDS.