Thanks for your question on Health Care Magic. I can understand your son s situation and problem. Atelectesis is partial collapse of lung tissue. Subsegmetal atelectesis is commonly due to collection of thick secretions in smaller airways. And infection is the most common cause for secretions. So your son needs broad spectrum antibiotic to cover infection. Mucolytic, expectorant and antioxidants drugs are needed to dilute the thick secretions, so that these are easily coughed out. Chest physiotherapy and deep breathing exercises are also helpful in this condition. So consult doctor, discuss all these and start appropriate treatment for your son. Hope I have solved your query. Wishing good health to your son. Thanks.