Final answer:
The life-threatening pneumothorax described, requiring immediate treatment to relieve trapped air and characterized by mediastinal shift and potential hemodynamic collapse, is known as a tension pneumothorax.
Step-by-step explanation:
The type of pneumothorax described in the question, characterized by a progressive accumulation of air in the pleural space, collapse of the affected lung, mediastinal shift, and potential hemodynamic collapse, is known as a tension pneumothorax. This condition is indeed life-threatening and requires prompt intervention to decompress the pleural cavity, typically by inserting a needle or chest tube to allow trapped air to escape. The emergency treatment restores proper lung function and stabilizes the patient's cardiovascular status, addressing symptoms like hypotension and cyanosis.