Pneumomediastinum is the presence of extraluminal gas within the mediastinum. Gas may come from lungs, trachea, central bronchi, esophagus, and the neck or abdomen.

Pneumoperitoneum represents free gas in the peritoneal cavity. 

Subcutaneous emphysema, strictly speaking, refers to air in the subcutaneous tissues. But the term is generally used to describe any soft tissue emphysema of the body wall or limbs since the air often dissects into the deeper soft tissue and musculature along fascial planes.

This patient developed those abnormalities after traumatic insertion of a tracheal tube.