Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Single AP upright portable view of the chest was obtained . Patient is status post median sternotomy and CABG . The cardiac and mediastinal silhouettes are grossly stable and enlarged . There is mild left base atelectasis . No large pleural effusion or pneumothorax . Subtle linear lucency below the diaphragm bilaterally concerning for pneumoperitoneum . This finding was paged to Dr . ___ on ___ at the time of discovery as well as placed into the wet read dashboard with urgent finding at 7 : 25 pm .
    OUTPUT:
    
Lucency below the diaphragms worrisome for pneumoperitoneum versus less likely artifact . At the time of this discovery , an abdomen CT had been ordered . Mild left base atelectasis . Status post median sternotomy and CABG .