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

<jats:p>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.</jats:p><jats:p>In total, 20 ARDS patients underwent 5 and 45 cmH<jats:sub>2</jats:sub>O computed tomography (CT) scans to measure lung recruitability. [<jats:sup>18</jats:sup>F]2-fluoro-2-deoxy-<jats:sc>d</jats:sc>-glucose ([<jats:sup>18</jats:sup>F]FDG) uptake and lung inhomogeneities were quantified with a positron emission tomography-CT scan at 10 cmH<jats:sub>2</jats:sub>O. We defined four compartments with normal/abnormal [<jats:sup>18</jats:sup>F]FDG uptake and lung homogeneity.</jats:p><jats:p>The homogeneous compartment with normal [<jats:sup>18</jats:sup>F]FDG uptake was primarily composed of well-inflated tissue (80±16%), double-sized in nondependent lung (32±27%<jats:italic>versus</jats:italic>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 [<jats:sup>18</jats:sup>F]FDG uptake was similarly distributed between the dependent and nondependent lung. The inhomogeneous compartment with normal [<jats:sup>18</jats:sup>F]FDG uptake represented 4% of the lung volume. The inhomogeneous compartment with high [<jats:sup>18</jats:sup>F]FDG uptake was preferentially located in the dependent lung (21±10%<jats:italic>versus</jats:italic>12±10%, p<0.0001), mostly at the open/closed interfaces and related to recruitability (r<jats:sup>2</jats:sup>=0.53, p<0.001).</jats:p><jats:p>The homogeneous lung compartment with normal inflation and [<jats:sup>18</jats:sup>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.</jats:p>