Lungs of patients with acute respiratory distress syndrome show diffuse inflammation in normally aerated regions: a [18F]-fluoro-2-deoxy-D-glucose PET/CT study

Objective: Neutrophilic inflammation plays a key role in the pathogenesis of acute respiratory distress syndrome (ARDS) and acute lung injury (ALI). Positron emission tomography (PET) with [ 18F]-fluoro-2-deoxy-D- glucose ( 18FDG) can be used to image cellular metabolism that, during lung inflammatory processes, likely reflects neutrophils activity. The aim of this study was to assess the magnitude and regional distribution of inflammatory metabolic activity in the lungs of patients with ALI/ARDS by PET with 18FDG. Design: Prospective clinical investigation. Patients: Ten patients with ALI/ARDS; four spontaneously breathing and two mechanically ventilated subjects, without known lung disease, served as controls. Interventions: In each individual we performed an 18FDG PET/computed tomography of the thorax. Measurements and Main Results: 18FDG cellular influx rate constant (K i) was computed for the imaged lung field and for regions of interest, grouping voxels with similar density. In all patients with ALI/ARDS, K i was higher than in controls, also after accounting for the increased lung density. K i values differed greatly among patients, but in all patients K i of the normally aerated regions was much higher (2- to 24-fold) than in controls. Whereas in some patients the highest K i values corresponded to regions with the lowest aeration, in others these regions had lower K i than normally and mildly hypoaerated regions. Conclusion: In patients with ALI/ARDS, undergoing mechanical ventilation since days, the metabolic activity of the lungs is markedly increased across the entire lung density spectrum. The intensity of this activation and its regional distribution, however, vary widely within and between patients.