Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Single AP portable view of the chest was obtained . There are relatively low lung volumes . The patient is status post median sternotomy . Left base opacity is seen , which may be due to atelectasis ; however , a small pleural effusion may be present , and a developing pneumonia is not excluded . There is slight blunting of the right costophrenic angle and a trace right pleural effusion is not excluded there either . The cardiac and mediastinal silhouettes are unremarkable . Evidence of air seen under the right hemidiaphragm , presumed postoperative .
    OUTPUT:
    
Left basilar opacity could be due to atelectasis ; however , developing infection is not excluded in the appropriate clinical setting . Blunting of the costophrenic angles , trace effusions not excluded . Evidence of pneumoperitoneum , presumed due to recent surgery .