Lung inhomogeneities, inflation and [F-18]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. [F-18] 2-fluoro-2-deoxy-D-glucose ([F-18] 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 [F-18] FDG uptake and lung homogeneity. The homogeneous compartment with normal [F-18] FDG uptake was primarily composed of well-inflated tissue (80 +/- 16%), double-sized in nondependent lung (32 +/- 27% versus 16 +/- 17%, p<0.0001) and decreased in size from mild, moderate to severe ARDS (33 +/- 14%, 26 +/- 20% and 5 +/- 9% of the total lung volume, respectively, p= 0.05). The homogeneous compartment with high [F-18] FDG uptake was similarly distributed between the dependent and nondependent lung. The inhomogeneous compartment with normal [F-18] FDG uptake represented 4% of the lung volume. The inhomogeneous compartment with high [F-18] FDG uptake was preferentially located in the dependent lung (21 +/- 10% versus 12 +/- 10%, p< 0.0001), mostly at the open/closed interfaces and related to recruitability (r(2)= 0.53, p<0.001). The homogeneous lung compartment with normal inflation and [F-18] 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.