Dynamics of PBF changes in regions of aspiration-induced acute lung injury

Ziel/Aim: Aspiration of gastric contents is the second most common clinical event associated with the development of the adult respiratory distress syndrome (ARDS) and the mortality for ARDS resulting from acid aspiration ranges from 40-50%. Regions of aspiration induced injury matches regions of high pulmonary blood flow (PBF) in the early stage of acute lung injury, as recently shown by us. The aim of this project was to characterize the dynamics of regional PBF distribution in dependence on time after injury. Methodik/Methods: The protocol was approved by the Animal Study Committee of the Landesdirektion Dresden. In 11 desflurane anesthetized, spontaneously breathing male Wistar rats the lung injury was achieved by instillation of 0.1 HCl (0.4 ml/kg body weight) through a tracheostomy tube. The animals were scanned with a dedicated small animal CT scanner before and after injury. The pulmonary blood flow in the lungs was imaged by dedicated positron emission tomography (PET) using intravenously infused Ga-68-labeled DOTA-modified microspheres (diameter 20 µm) at 10 (6 animals) and 120 min (5 animals) after aspiration. CT- and PET-images were co-registered. Areas of injury, identified as new high density regions in lung CT-images after aspiration, were marked with a spherical mask and regions of interest (ROI) were derived using a threshold of 80% of maximum activity in the mask. Identical masks were used at the contralateral lung as reference. PBF in the injury ROI was calculated as activity fraction of the reference PBF region. The PBF in injury was compared with the reference side using the Wilcoxon matched-pairs signed rank test. The PBF-fraction at different time points was compared between the groups by unpaired t-test with Welch's correction. Ergebnisse/Results: CT images after aspiration showed areas of lung injury different in location and size within the two groups. Fraction of PBF in injured regions was higher at 10 min {1.34 (1.15-1.45) (median (interquartile range)} compared to 120 min (0.9 (0.85-1.06); P=0.0014) after aspiration. The intra-individual difference was determined by a high PBF in injured lung regions compared to the contralateral reference side at 10 min after injury (P = 0.03), whereas at 120 min after aspiration, injured regions have shown similar PBF compared to the contralateral reference side (P=0.81). Schlussfolgerungen/Conclusions: Regional PBF was increased 10 minutes after acid aspiration in regions of injury. This effect disappears within two hours after injury in anesthetized rats. This observed change in PBF after aspiration-induced acute lung injury seems to be important in early targeted treatment of acid aspiration.