Which condition is treated by inserting a thoracostomy tube?

A thoracostomy tube is specifically indicated for the treatment of a pneumothorax, which is a condition where air accumulates in the pleural space, leading to lung collapse. The insertion of a thoracostomy tube allows for the removal of air, and in some cases, fluid, from the pleural cavity, which helps re-expand the lung and restore normal respiratory function.

In contrast, pneumonia, asthma, and bronchitis are respiratory conditions primarily managed through medications, such as antibiotics for pneumonia or bronchodilators for asthma, rather than through invasive procedures like a thoracostomy. Thus, the correct application of a thoracostomy tube is specifically tied to managing a pneumothorax, making it the appropriate answer in this context.