Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Median sternotomy and CABG clips are re- demonstrated . Lung volumes remain low . Heart size remains mild to moderately enlarged . Mediastinal and hilar contours are grossly unremarkable and unchanged . There is crowding of bronchovascular structures with possible mild pulmonary vascular congestion , but no overt pulmonary edema . Patchy airspace opacities the lung bases likely reflect areas of atelectasis in the setting of low lung volumes , however infection can not be completely excluded . No pleural effusion or iron pneumothorax . There are moderate multilevel degenerative changes in the thoracic spine .
    OUTPUT:
    
Low lung volumes with possible mild pulmonary vascular congestion and bibasilar patchy opacities , likely atelectasis , but infection can not be excluded .