Which of the following symptoms would most likely indicate a tension pneumothorax?

A tension pneumothorax occurs when air enters the pleural space and cannot escape, leading to increased pressure that compresses the lung and shifts mediastinal structures. Tracheal deviation is one of the hallmark signs of a tension pneumothorax. When pressure builds up in one side of the thoracic cavity, it pushes the trachea away from the affected lung toward the opposite side. This is a critical clinical finding that helps differentiate tension pneumothorax from other types of pneumothorax or respiratory distress.

In contrast, decreased breath sounds on the affected side and unilateral chest expansion may indicate that there is a pneumothorax, but they are not as definitive as tracheal deviation for tension pneumothorax specifically. Persistent coughing is not a primary symptom associated with tension pneumothorax and does not directly indicate the presence of trapped air or the resultant pressure effects on thoracic structures.