Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Status post median sternotomy . Chest tubes project over both hemithoraces . Low bilateral lung volumes with bibasilar and mid lung atelectasis . No pneumothorax identified . A small amount of pneumomediastinum , likely post operative . The size of the cardiomediastinal silhouette is enlarged and may be secondary to the low inspiratory lung volumes and post surgical changes .
    OUTPUT:
    
Chest tubes project over each hemithorax . Status post median sternotomy . Pneumomediastinum , as expected postoperatively . Low bilateral lung volumes with mid to lower lung zone atelectasis . Enlarged cardiomediastinal silhouette , which may be secondary to low inspiratory lung volumes and postsurgical changes .